Global Climate Change Leads to Mistimed Avian Reproduction

Climate change reduces the tension of conflicting selection pressures on breeding date in a passerine bird

Unpredictably fluctuating environments create complex selective landscapes that shape the distribution of key life history traits. Identifying the mechanisms behind dynamic patterns of selection is difficult, yet essential for predicting responses to climate change. We combine long-term measures with field manipulation of natural selection on breeding date in a wild bird to investigate whether highly variable spring cold snaps drive fluctuating selection. We show that variation in cold snap intensity leads to fluctuating selection on breeding date-in weak cold snap years, selection was consistently negative; however, in strong cold snap years, its direction reversed. These patterns were mirrored in a field experiment; nests that were food supplemented during cold snaps avoided cold snap mortality leading earlier breeders to have higher fitness. In contrast, in the non-supplemented group earlier breeders had higher cold snap nest mortality and selection was positive. Using nearly a century of climate data, we show that cold snaps are becoming less frequent and paradoxically occurring later which should allow earlier breeders to avoid them, potentially releasing conflicting selection pressures and facilitating a rapid phenological shift. Thus, rather than constraining a species' ability to adapt, climate change can enable a rapid shift to a new phenotypic optimum.

Avian migration clocks in a changing world

Avian long-distance migration requires refined programming to orchestrate the birds' movements on annual temporal and continental spatial scales. Programming is particularly important as long-distance movements typically anticipate future environmental conditions. Hence, migration has long been of particular interest in chronobiology. Captivity studies using a proxy, the shift to nocturnality during migration seasons (i.e., migratory restlessness), have revealed circannual and circadian regulation, as well as an innate sense of direction. Thanks to rapid development of tracking technology, detailed information from free-flying birds, including annual-cycle data and actograms, now allows relating this mechanistic background to behaviour in the wild. Likewise, genomic approaches begin to unravel the many physiological pathways that contribute to migration. Despite these advances, it is still unclear how migration programmes are integrated with specific environmental conditions experienced during the journey. Such knowledge is imminently important as temporal environments undergo rapid anthropogenic modification. Migratory birds as a group are not dealing well with the changes, yet some species show remarkable adjustments at behavioural and genetic levels. Integrated research programmes and interdisciplinary collaborations are needed to understand the range of responses of migratory birds to environmental change, and more broadly, the functioning of timing programmes under natural conditions.

Effects of meteorology and lunar cycle on the post-thawing quality of avian sperm

Introduction

Various climatological and lunar cycle parameters have a direct impact on animal reproduction, and in the case of the avian species, spermatozoa are extremely sensitive to heat stress. These parameters could influence sperm freezability, which will ultimately affect post-thawing semen quality, being sperm motility in roosters a relevant indicator of this quality as it is highly related to fertility. Therefore, the objective of the present study is to determine which are the climatological and lunar cycle parameters that have a greater effect on sperm freezability in roosters.

Methods

Sperm was obtained from 16 Utrerana breed roosters and a total of 27 replicates were performed. A pool was made with those ejaculates that met the minimum quality criteria for each replicate, and four freezing-thawing samples per replicate were analyzed. The straws were thawed, and sperm motility was evaluated, classifying the results obtained into four seminal quality groups according to the guidelines of the Food and Agriculture Organization of the United Nations (Group 1: Good, Group 2: Satisfactory, Group 3: Acceptable but undesirable and Group 4: Unsatisfactory). The following traits were recorded for each day of semen collection: maximum temperature, minimum temperature, maximum barometric pressure, minimum barometric pressure, maximum gust, wind direction, mean wind speed, sunshine hours, rainfall, moon phase, and percentage of illuminated lunar surface over the total area.

Results

A discriminant canonical analysis was performed to determine which of these parameters offered the most information when classifying an ejaculate in each quality group, with minimum temperature, the new moon as moon phase, minimum barometric pressure, and rainfall being the most significant variables.

Discussion

According to the results obtained, semen quality decreases when temperature and precipitation are lower, pressure is higher, and when there is a new moon phase. Therefore, these environmental conditions should be avoided for sperm collection and processing.

Odours of caterpillar-infested trees increase testosterone concentrations in male great tits

Trees release Herbivore-Induced Plant Volatiles (HIPVs) into the air in response to damage inflicted by insects. It is known that songbirds use those compounds to locate their prey, but more recently the idea emerged that songbirds could also use those odours as cues in their reproductive decisions, as early spring HIPVs may contain information about the seasonal timing and abundance of insects. We exposed pre-breeding great tits (Parus major) to the odours of caterpillar-infested trees under controlled conditions, and monitored reproduction (timing of egg laying, number of eggs, egg size) and two of its main hormonal drivers (testosterone and 17β-estradiol in males and females, respectively). We found that females exposed to HIPVs did not advance their laying dates, nor laid larger clutches, or larger eggs compared to control females. 17β-estradiol concentrations in females were also similar between experimental and control birds. However, males exposed to HIPVs had higher testosterone concentrations during the egg-laying period. Our study supports the hypothesis that insectivorous songbirds are able to detect minute amounts of plant odours. The sole manipulation of plant scents was not sufficient to lure females into a higher reproductive investment, but males increased their reproductive effort in response to a novel source of information for seasonal breeding birds.

Will a changing climate affect hatching success in cavity-nesting birds: A case study with Eastern Bluebirds (Sialia sialis)?

A significant body of evidence indicates that climate change is influencing many aspects of avian ecology. Yet, how climate change is affecting, and is expected to influence some aspects of the breeding ecology of cavity-nesting birds remains uncertain. To explore the potential linkage between timing of first clutch, and the influence of ambient temperature on hatching success, we used Eastern Bluebird (Sialia sialis) nest records over a nine-year period from Alabama, USA. We investigated changes to annual clutch initiation dates, as well as variability in hatching success associated with ambient air temperatures during the incubation period. Using a simple linear model, we observed earlier annual egg laying dates over the nine years of this study with a difference of 24 days between earliest egg-laying date of the season. Daily temperature minima increased 2 °C across the nine-year time frame of this study. These data also indicate that Eastern Bluebird hatching success was the highest when mean ambient air temperature during incubation was between 19 °C and 24 °C (78%, as opposed to 69% and 68% above and below this temperature range, respectively). Our findings of increasing maxima, earlier maxima each year, and the lower minima of temperatures within our study area could expand the breadth of temperatures experienced by nesting Eastern Bluebirds possibly exposing them to temperatures outside of what promotes nesting success. These findings with a cavity-nesting bird highlight an optimal range of ambient temperatures associated with highest hatching success, conditions likely to be affected by climate change.

Inconsistent shifts in warming and temperature variability are linked to reduced avian fitness

As the climate has warmed, many birds have advanced their breeding timing. However, as climate change also changes temperature distributions, breeding earlier might increase nestling exposure to either extreme heat or cold. Here, we combine >300,000 breeding records from 24 North American birds with historical temperature data to understand how exposure to extreme temperatures has changed. Average spring temperature increased since 1950 but change in timing of extremes was inconsistent in direction and magnitude; thus, populations could not track both average and extreme temperatures. Relative fitness was reduced following heatwaves and cold snaps in 11 and 16 of 24 species, respectively. Latitudinal variation in sensitivity in three widespread species suggests that vulnerability to extremes at range limits may contribute to range shifts. Our results add to evidence demonstrating that understanding individual sensitivity and its links to population level processes is critical for predicting vulnerability to changing climates.

Co-migration fidelity at a stopover site increases over time in African-European migratory landbirds

Migratory species are changing their timing of departure from wintering areas and arrival to breeding sites (i.e. migration phenology) in response to climate change to exploit maximum food availability at higher latitudes and improve their fitness. Despite the impact of changing migration phenology at population and community level, the extent to which individual and species-specific response affects associations among co-migrating species has been seldom explored. By applying temporal co-occurrence network models on 15 years of standardized bird ringing data at a spring stopover site, we show that African-European migratory landbirds tend to migrate in well-defined groups of species with high temporal overlap. Such 'co-migration fidelity' significantly increased over the years and was higher in long-distance (trans-Saharan) than in short-distance (North African) migrants. Our findings suggest non-random patterns of associations in co-migrating species, possibly related to the existence of regulatory mechanisms associated with changing climate conditions and different uses of stopover sites, ultimately influencing the global economy of migration of landbirds in the Palearctic-African migration system.

Citizen science data reveal regional heterogeneity in phenological response to climate in the large milkweed bug, Oncopeltus fasciatus

Regional populations of geographically widespread species may respond to different environmental factors across the species' range, generating divergent effects of climate change on life-history phenology. Using thousands of citizen science observations extracted from iNaturalist and associated with corresponding temperature, precipitation, elevation, and daylength information, we examined the drivers of adult mating and of nymphal phenology, development, and group size for populations of the large milkweed bug, Oncopeltus fasciatus, in different ecoregions. Research-grade iNaturalist images were correctly identified 98.3% of the time and yielded more than 3000 observations of nymphal groups and 1000 observations of mating adults spanning 18 years. Mating phenology showed distinct regional patterns, ranging from year-round mating in California to temporally restricted mating in the Great Lakes Northeastern Coast ecoregion. Relative temperature increases of 1°C for a given daylength expanded the mating season by more than a week in western ecoregions. While increases in relative temperature delayed mating phenology in all ecoregions, greater winter precipitation advanced mating in the California ecoregion. In the eastern ecoregions, nymphal phenology was delayed by increases in summer rainfall but was advanced by relative temperature increases, whereas in western regions, relative temperature increases delayed nymphal phenology. Furthermore, accumulated growing degree days (AGDD) was a poor predictor of developmental progression, as we found a positive but weak correlation between AGDD and age structure only for the Appalachian Southeast North America and the Great Lakes Northern Coast ecoregions. These complex phenological responses of O. fasciatus are just one example of how populations may be differentially susceptible to a diversity of climatic effects; using data across a species' whole distribution is critical for exposing regional variations, especially for species with large, continental-scale ranges. This study demonstrates the potential of photodocumented biodiversity data to aid in the monitoring of life history, host plant-insect interactions, and climate responsiveness.

Complex relationships between climate and reproduction in a resident montane bird

Animals use climate-related environmental cues to fine-tune breeding timing and investment to match peak food availability. In birds, spring temperature is a commonly documented cue used to initiate breeding, but with global climate change, organisms are experiencing both directional changes in ambient temperatures and extreme year-to-year precipitation fluctuations. Montane environments exhibit complex climate patterns where temperatures and precipitation change along elevational gradients, and where exacerbated annual variation in precipitation has resulted in extreme swings between heavy snow and drought. We used 10 years of data to investigate how annual variation in climatic conditions is associated with differences in breeding phenology and reproductive performance in resident mountain chickadees (Poecile gambeli) at two elevations in the northern Sierra Nevada mountains, USA. Variation in spring temperature was not associated with differences in breeding phenology across elevations in our system. Greater snow accumulation was associated with later breeding initiation at high, but not low, elevation. Brood size was reduced under drought, but only at low elevation. Our data suggest complex relationships between climate and avian reproduction and point to autumn climate as important for reproductive performance, likely via its effect on phenology and abundance of invertebrates.

The effect of insect food availability on songbird reproductive success and chick body condition: Evidence from a systematic review and meta-analysis

Reports of declines in abundance and biomass of insects and other invertebrates from around the world have raised concerns about food limitation that could have profound impacts for insectivorous species. Food availability can clearly affect species; however, there is considerable variation among studies in whether this effect is evident, and thus a lack of clarity over the generality of the relationship. To understand how decreased food availability due to invertebrate declines will affect bird populations, we conducted a systematic review and used meta-analytic structural equation modelling, which allowed us to treat our core variables of interest as latent variables estimated by the diverse ways in which researchers measure fecundity and chick body condition. We found a moderate positive effect of food availability on chick body condition and a strong positive effect on reproductive success. We also found a negative relationship between chick body condition and reproductive success. Our results demonstrate that food is generally a limiting factor for breeding songbirds. Our analysis also provides evidence for a consistent trade-off between chick body condition and reproductive success, demonstrating the complexity of trophic dynamics important for these vital rates.

Contrasted impacts of weather conditions in species sensitive to both survival and fecundity: A montane bird case study

There is growing evidence that the Earth's climate is undergoing profound changes that are affecting biodiversity worldwide. This gives rise to the pressing need to develop robust predictions on how species will respond in order to inform conservation strategies and allow managers to adapt mitigation measures accordingly. While predictions have begun to emerge on how species at the extremes of the so-called slow-fast continuum might respond to climate change, empirical studies for species for which all demographic traits contribute relatively equally to population dynamics are lacking. Yet, climate change is expected to strongly affect them throughout their entire lifecycle. We built a 21-year integrated population model to characterize the population dynamics of the rock partridge (Alectoris graeca) in France, and tested the influence of nine weather covariates on demographic parameters. As predicted, both annual survival and breeding success were affected by weather covariates. Thick snow cover during winter was associated with low survival and small brood size the following breeding season. Brood size was higher with intermediate winter temperatures and snowmelt timing, positively correlated to breeding period temperature, but negatively correlated to temperature during the coldest fortnight and precipitation during the breeding period. Survival was positively correlated to winter temperature, but negatively to breeding period precipitation. Large-scale indices indicated that cold and wet winters were associated with small brood size the following breeding season but with high survival. Expected changes of weather conditions due to climate change are likely to impact demographic traits of the rock partridge both positively and negatively depending on the traits and on the affected weather variables. Future population dynamics will thus depend on the magnitude of these different impacts. Our study illustrates the difficulty to make strong predictions about how species with a population dynamic influenced by both survival and fecundity will respond to climate change.

Phenotype-environment mismatch errors enhance lifetime fitness in wild red squirrels

Mismatches between an organism's phenotype and its environment can result in short-term fitness costs. Here, we show that some phenotype-environment mismatch errors can be explained by asymmetrical costs of different types of errors in wild red squirrels. Mothers that mistakenly increased reproductive effort when signals of an upcoming food pulse were absent were more likely to correctly increase effort when a food pulse did occur. However, mothers that failed to increase effort when cues of an upcoming food pulse were present suffered lifetime fitness costs that could only be offset through food supplementation. In fluctuating environments, such phenotype-environment mismatches may therefore reflect a bias to overestimate environmental cues and avoid making the costliest error, ultimately enhancing lifetime fitness.

Testing the environmental buffering hypothesis of cooperative breeding in the Seychelles warbler

Species are facing environmental challenges caused by rapidly changing environments. Globally, extreme weather events, like droughts or extreme rainfall, are increasing in frequency. Natural selection usually acts slowly, while adaptations through phenotypic plasticity are limited. Therefore, organisms may utilise other mechanisms to cope with such rapid change. Cooperative breeding is hypothesised to be one such mechanism, as helpers could increase survival probabilities of offspring, especially in harsh years. Rainfall is a cue for onset of breeding in many tropical species, to ensure young are born when food abundance is highest. Using 21 years of data, we investigate the effect of rainfall on social behaviour and life history in the insectivorous Seychelles warbler (Acrocephalus sechellensis), a facultative cooperative breeder. We found that low rainfall is associated with reduced reproductive output and possibly with decreased survival. However, there were no statistical differences in response between groups with helpers, groups with only non-helping subordinates, and breeding pairs without subordinates. With low rainfall, more sons (the sex less likely to help) were produced, and those subordinate males already present were less likely to help. Thus, in contrast to expectations, cooperative breeding does not seem to buffer against harsh environments in Seychelles warblers, indicating that group living may be costly and thus not a mechanism for coping with changing environments. Our study showed that the interaction between the environment and life histories, including social behaviour, is complex, but that this interaction is important to consider when studying the impact of changing environments on species survival.

Resilience of Avian Communities to Urbanization and Climate Change: an Integrative Review

The concept of ecological resilience is widely used to assess how species and ecosystems respond to external stressors but is applied infrequently at the level of the community or to chronic, ongoing disturbances. In this review, we first discuss the concept of ecological resilience and methods for quantifying resilience in ecological studies. We then synthesize existing evidence for the resilience of avian communities to climate change and urbanization, two chronic disturbances that are driving global biodiversity loss, and conclude with recommendations for future directions. We only briefly discuss the theoretical framework behind ecological resilience and species-specific responses to these two major disturbances, because numerous reviews already exist on these topics. Current research suggests strong heterogeneity in the responses and resilience of bird communities to urbanization and climate change, although community disassembly and reassembly is high following both disturbances. To advance our understanding of community resilience to these disturbances, we recommend five areas of future study (1) the development of a standardized, comprehensive community resilience index that incorporates both adaptive capacity and measures of functional diversity, (2) measurement/modeling of both community resistance and recovery in response to disturbance, (3) multi-scale and/or multi-taxa studies that include three-way interactions between plants, animals, and climate, (4) studies that incorporate interactions between disturbances, and (5) increased understanding of interactions between ecological resilience and socio-ecological dynamics. Advancement in these areas will enhance our ability to predict and respond to the rapidly accelerating effects of climate change and urbanization.

Phenological Response of Flood Plain Forest Ecosystem Species to Climate Change during 1961–2021

The present study analyses 61 years of phenological observations (1961–2021) of five herb, five shrub, four tree, and one bird species representing the prevalent spring species of floodplain forest ecosystems in the Czech Republic, central Europe. The in situ observations were conducted at the Vranovice site (48°48′ N, 16°46′ E, 170 m above mean sea level) representing the Plaček’ forest National Reserve. The observed plants and bird species showed statistically significant (p < 0.05) shifts in phenological terms to an earlier date of the year, but the rate of the shift among the observed species differed. The most progressive shifts were detected for the herbs (14 days), followed by the shrubs (13 days), trees (9 days), and finally by the bird species (8 days). All the phenophases were significantly correlated with the daily maximum temperature (r = 0.72–0.91). The results also showed a decline in the correlation for species among the phenophases of the herbs and trees. The phenophases that were highly correlated in the past were less correlated and had higher variability in the last decades. We conclude that the phenological response of the ecosystem to warming in the spring resulted in higher variability and a lower correlation among the observed phenophases mainly caused by the most expressive phenological shifts of the early herbs.

Improved breeding parameters in the pied flycatcher with reduced pollutant emissions from a copper smelter

In recent decades, industrial emissions have been reduced in many countries, which provides an opportunity for the recovery of polluted ecosystems. However, our knowledge of the rate and factors facilitating the recovery of local bird populations after pollution abatement is incomplete. Long-term (1989-2021) annual observations on nest-box populations of a passerine bird, Ficedula hypoleuca, were used to analyze temporal dynamics of breeding parameters following a 50-fold reduction of industrial emissions from the Middle Ural copper smelter (MUCS) according to pollution zone, habitat, air temperature, and breeding density. In the heavily polluted (impact) zone (1-2 km of MUCS), egg and fledgling production were strongly impaired compared to the moderately polluted (buffer zone, 4-8 km of MUCS) and unpolluted control zone (16-27 km of MUCS). During the study period, the laying date advanced along with increasing spring air temperatures. The clutch size increased in the impact zone by 26%, in the buffer zone by 10%, and in control by 5%. The number of fledglings increased in the impact zone by 102% and the buffer zone by 17%. In the most recent year (2021), mean laying date, clutch size, fledgling production, and the frequency of nests with unhatched eggs in the impact zone did not reach the control level, whereas the frequency of nests with perished chicks did not differ among zones. Breeding parameters of birds in the impact zone improved slowly, likely due to the slow recovery of habitats. We conclude that bird reproduction may require many decades to recover fully in the heavily polluted zone.

Variability in Arrival Time of White Storks (Ciconia ciconia L.): Impact of Age, Interindividual Variation, and Global Change

Global changes are inducing migratory birds to advance their annual cycle. However, changes in the time of arrival at their breeding grounds have significant fitness implications. This study aims to identify factors affecting the variability in arrival time of migratory white storks (Ciconia ciconia L.) and to determine if their arrival at North African breeding grounds is occurring earlier. We monitored the arrival of ringed white storks at a breeding colony in Algeria between 2017 and 2021. The birds arrived at this breeding colony over an extended period spanning mid-December to mid-June each year. We found that stork arrival was negatively correlated with age and year of arrival, with older birds arriving first and stragglers consisting of first- and second-year birds arriving later. Notably, arrivals have been shifting toward earlier dates at this breeding ground. Furthermore, cluster analysis of arrival dates for each age-class revealed two distinct groups comprising early and late arrivals. Advancement of the annual cycle of the North African white stork population is consistent with phenological shifts induced by global changes and that have been recorded globally in a wide range of living organisms.

Mitigating human impacts including climate change on proliferative kidney disease in salmonids of running waters

Over the last two decades, an increasing number of reports have identified a decline in salmonid populations, possibly linked to infection with the parasite Tetracapsuloides bryosalmonae and the corresponding disease, that is, proliferative kidney disease (PKD). The life cycle of this myxozoan parasite includes sessile bryozoan species as invertebrate host, which facilitates the distribution of the parasite in running waters. As the disease outcome is temperature dependent, the impact of the disease on salmonid populations is increasing with global warming due to climate change. The goal of this review is to provide a detailed overview of measures to mitigate the effects of PKD on salmonid populations. It first summarizes the parasite life cycle, temperature-driven disease dynamics and new immunological and molecular research into disease resistance and, based on this, discusses management possibilities. Sophisticated management actions focusing on local adaptation of salmonid populations, restoration of the riverine ecosystem and keeping water temperatures cool are necessary to reduce the negative effects of PKD. Such actions include temporary stocking with PKD-resistant salmonids, as this may assist in conserving current populations that fail to reproduce.

Mismatch-induced growth reductions in a clade of Arctic-breeding shorebirds are rarely mitigated by increasing temperatures

In seasonal environments subject to climate change, organisms typically show phenological changes. As these changes are usually stronger in organisms at lower trophic levels than those at higher trophic levels, mismatches between consumers and their prey may occur during the consumers' reproduction period. While in some species a trophic mismatch induces reductions in offspring growth, this is not always the case. This variation may be caused by the relative strength of the mismatch, or by mitigating factors like increased temperature-reducing energetic costs. We investigated the response of chick growth rate to arthropod abundance and temperature for six populations of ecologically similar shorebirds breeding in the Arctic and sub-Arctic (four subspecies of Red Knot Calidris canutus, Great Knot C. tenuirostris and Surfbird C. virgata). In general, chicks experienced growth benefits (measured as a condition index) when hatching before the seasonal peak in arthropod abundance, and growth reductions when hatching after the peak. The moment in the season at which growth reductions occurred varied between populations, likely depending on whether food was limiting growth before or after the peak. Higher temperatures led to faster growth on average, but could only compensate for increasing trophic mismatch for the population experiencing the coldest conditions. We did not find changes in the timing of peaks in arthropod availability across the study years, possibly because our series of observations was relatively short; timing of hatching displayed no change over the years either. Our results suggest that a trend in trophic mismatches may not yet be evident; however, we show Arctic-breeding shorebirds to be vulnerable to this phenomenon and vulnerability to depend on seasonal prey dynamics.

Individual variation in reaction norms but no directional selection in reproductive plasticity of a wild passerine population

In the plant-insect-insectivorous bird food chain, directional changes in climate can result in mismatched phenology, potentially affecting selection pressures. Phenotypic plasticity in the timing of breeding, characterized by reaction norm slopes, can help maximize fitness when faced with earlier prey emergence. In temperate passerines, the timing of tree budburst influences food availability for chicks through caterpillar phenology and the resulting food abundance patterns. Thus, the timing of tree budburst might serve as a more direct proxy for the cue to time egg-laying. The evolutionary potential of breeding plasticity relies on heritable variation, which is based upon individual variation, yet studies on individual variation in plasticity are few. Here, we tested for the laying date-budburst date and the clutch size-laying date reaction norms, and examined 1) the among-individual variance in reaction norm intercepts and slopes; and 2) the selection differentials and gradients on these intercepts and slopes. Using long-term data of oak (genus Quercus) budburst and blue tit (Cyanistes caeruleus) reproduction, we applied within-subject centering to detect reaction norms, followed by bivariate random regression to quantify among-individual variance in reaction norm properties and their covariance with fitness. Individuals significantly differed in intercepts and slopes of both laying date-budburst date and clutch size-laying date reaction norms, and directional selection was present for an earlier laying date and a larger clutch size (intercepts), but not on plasticity (slopes). We found that individuals have their own regimes for adjusting egg-laying and clutch size. This study provides further support of individual variation of phenotypic plasticity in birds.

Limited increase in asynchrony between the onset of spring green-up and the arrival of a long-distance migratory bird

For many migrant bird species around the world, climate change has been shown to induce changes in the timings of arrival and the onset of spring food availability at breeding sites. However, whether such changes enlarged asynchrony between the timings of spring arrival of long-distance migratory birds and onset of vegetation greenness increase remain controversial. We used a 29-year phenological dataset to investigate the temporal changes in spring first-sighting date (FSD) of a long-distance migratory bird (barn swallow, Hirundo rustica), from observations at 160 local breeding sites across northern China, and the vegetation green-up onset date (VGD), determined from satellite observations of vegetation greenness. We found that both FSD and VGD trended earlier at over two-thirds of the breeding sites. FSD significantly advanced at 26.9% of the sites, and VGD significantly advanced at 23.8% of the sites. The degree of asynchrony between FSD and VGD changed significantly at one-third of the breeding sites (22.5% with an increase versus 11.3% with a decrease), leading to a limited increase of phenological mismatch. We speculated that climate change did not disrupt the climatic connections between most breeding sites and corresponding non-breeding sites (wintering grounds and migration routes). Our findings suggest that climate change may not greatly increase phenological mismatch between first arrival date of barn swallows and VGD at breeding sites. Importantly, this study should serve as a cue to encourage ecologists and conservation biologists to expand the context under which to explore the ecological consequences of phenological shifts beyond asynchrony, such as individual survival, population demography and ecosystem-level consequences.

Climate change effects on animal ecology: butterflies and moths as a case study

Butterflies and moths (Lepidoptera) are one of the most studied, diverse, and widespread animal groups, making them an ideal model for climate change research. They are a particularly informative model for studying the effects of climate change on species ecology because they are ectotherms that thermoregulate with a suite of physiological, behavioural, and phenotypic traits. While some species have been negatively impacted by climatic disturbances, others have prospered, largely in accordance with their diversity in life-history traits. Here we take advantage of a large repertoire of studies on butterflies and moths to provide a review of the many ways in which climate change is impacting insects, animals, and ecosystems. By studying these climate-based impacts on ecological processes of Lepidoptera, we propose appropriate strategies for species conservation and habitat management broadly across animals.

From individual to population level: Temperature and snow cover modulate fledging success through breeding phenology in greylag geese (Anser anser)

Local weather conditions may be used as environmental cues by animals to optimize their breeding behaviour, and could be affected by climate change. We measured associations between climate, breeding phenology, and reproductive output in greylag geese (Anser anser) across 29 years (1990-2018). The birds are individually marked, which allows accurate long-term monitoring of life-history parameters for all pairs within the flock. We had three aims: (1) identify climate patterns at a local scale in Upper Austria, (2) measure the association between climate and greylag goose breeding phenology, and (3) measure the relationship between climate and both clutch size and fledging success. Ambient temperature increased 2 °C across the 29-years study period, and higher winter temperature was associated with earlier onset of egg-laying. Using the hatch-fledge ratio, average annual temperature was the strongest predictor for the proportion of fledged goslings per season. There is evidence for an optimum time window for egg-laying (the earliest and latest eggs laid had the lowest fledging success). These findings broaden our understanding of environmental effects and population-level shifts which could be associated with increased ambient temperature and can thus inform future research about the ecological consequences of climate changes and reproductive output in avian systems.

Spring understory herbs flower later in intensively managed forests

Many organisms respond to anthropogenic environmental change through shifts in their phenology. In plants, flowering is largely driven by temperature, and therefore affected by climate change. However, on smaller scales climatic conditions are also influenced by other factors, including habitat structure. A group of plants with a particularly distinct phenology are the understory herbs in temperate European forests. In these forests, management alters tree species composition (often replacing deciduous with coniferous species) and homogenizes stand structure, and as a consequence changes light conditions and microclimate. Forest management should thus also affect the phenology of understory herbs. To test this, we recorded the flowering phenology of 16 early-flowering herbs on 100 forest plots varying in management intensity, from near-natural to intensely managed forests, in central and southern Germany. We found that in forest stands with a high management intensity, such as Norway spruce plantations, the plants flowered on average about 2 weeks later than in unmanaged forests. This was largely because management also affected microclimate (e.g., spring temperatures of 5.9°C in managed coniferous, 6.7 in managed deciduous, and 7.0°C in unmanaged deciduous plots), which in turn affected phenology, with plants flowering later on colder and moister forest stands (+4.5 d per -1°C and 2.7 d per 10% humidity increase). Among forest characteristics, the percentage of conifers had the greatest influence on microclimate, but also the age, overall crown projection area, structural complexity and spatial distribution of the forest stands. Our study indicates that forest management alters plant phenology, with potential far-reaching consequences for the ecology and evolution of understorey communities. More generally, our study demonstrates that besides climate change other drivers of environmental change, too, can influence the phenology of organisms.

Exposure to artificial light at night accelerates but does not override latitude-dependent seasonal reproductive response in a North American songbird

In the modern era of industrialization, illuminated nights have become a common defining feature of human-occupied environments, particularly cities. Artificial light at night (ALAN) imposes several known negative impacts on the neuroendocrine system, metabolism, and seasonal reproduction of species living in the wild. However, we know little about the impact of ALAN on populations of birds that either live year-round in the same location or move to different latitudes across seasons. To test whether ALAN has a differing impact on the reproductive timing of bird populations that winter in sympatry but breed at different latitudes, we monitored sedentary and migratory male dark-eyed juncos that were or were not exposed to low intensity (∼2.5 ± 0.5 lux) ALAN. All groups were held in common conditions and day length was gradually increased to mimic natural day length changes (NDL). We assessed seasonal reproductive response from initiation to termination of the breeding cycle. As expected based on earlier research, the sedentary birds exhibited earlier gonadal recrudescence and terminated breeding later than the migratory birds. In addition, resident and migrant birds exposed to ALAN initiated gonadal recrudescence earlier and terminated reproductive events sooner as compared to their conspecifics experiencing NDL. Importantly, the difference in the reproductive timing of sedentary and migratory populations was maintained even when exposed to ALAN. This variation in the seasonal reproductive timing may likely have a genetic basis or be the result of early developmental effects imposed due to different light regimes related to the latitude of origin. This study reveals first that ALAN accelerated reproductive development across both migrants and residents and second that latitude-dependent variation in reproductive timing is maintained despite exposure to ALAN. These results corroborate a relationship between latitude, population, and reproductive timing while also revealing ALAN's impact on seasonal reproductive timing. This study reveals that, ALAN accelerated reproductive development but maintained latitude-dependent variation in reproductive timing across both migrant and resident bird populations.

Nocturnal foraging lifts time constraints in winter for migratory geese but hardly speeds up fueling

Climate warming advances the optimal timing of breeding for many animals. For migrants to start breeding earlier, a concurrent advancement of migration is required, including premigratory fueling of energy reserves. We investigate whether barnacle geese are time constrained during premigratory fueling and whether there is potential to advance or shorten the fueling period to allow an earlier migratory departure. We equipped barnacle geese with GPS trackers and accelerometers to remotely record birds’ behavior, from which we calculated time budgets. We examined how time spent foraging was affected by the available time (during daylight and moonlit nights) and thermoregulation costs. We used an energetic model to assess onset and rates of fueling and whether geese can further advance fueling by extending foraging time. We show that, during winter, when facing higher thermoregulation costs, geese consistently foraged at night, especially during moonlit nights, in order to balance their energy budgets. In spring, birds made use of the increasing day length and gained body stores by foraging longer during the day, but birds stopped foraging extensively during the night. Our model indicates that, by continuing nighttime foraging throughout spring, geese may have some leeway to advance and increase fueling rate, potentially reaching departure body mass 4 days earlier. In light of rapid climatic changes on the breeding grounds, whether this advancement can be realized and whether it will be sufficient to prevent phenological mismatches remains to be determined.

Individual reversible plasticity as a genotype-level bet-hedging strategy

Reversible plasticity in phenotypic traits allows organisms to cope with environmental variation within lifetimes, but costs of plasticity may limit just how well the phenotype matches the environmental optimum. An additional adaptive advantage of plasticity might be to reduce fitness variance, in other words: bet-hedging to maximize geometric (rather than simply arithmetic) mean fitness. Here, we model the evolution of plasticity in the form of reaction norm slopes, with increasing costs as the slope or degree of plasticity increases. We find that greater investment in plasticity (i.e. a steeper reaction norm slope) is favoured in scenarios promoting bet-hedging as a response to multiplicative fitness accumulation (i.e. coarser environmental grains and fewer time steps prior to reproduction), because plasticity lowers fitness variance across environmental conditions. In contrast, in scenarios with finer environmental grain and many time steps prior to reproduction, bet-hedging plays less of a role and individual-level optimization favours evolution of shallower reaction norm slopes. However, the opposite pattern holds if plasticity costs themselves result in increased fitness variation, as might be the case for production costs of plasticity that depend on how much change is made to the phenotype each time step. We discuss these contrasting predictions from this partitioning of adaptive plasticity into short-term individual benefits versus long-term genotypic (bet-hedging) benefits, and how this approach enhances our understanding of the evolution of optimum levels of plasticity in examples from thermal physiology to advances in avian lay dates.

Temperate deciduous shrub phenology: the overlooked forest layer

Temperate deciduous shrub phenology plays a pivotal role in forest ecology by regulating the timing of suitable habitat and food of a range of organisms as well as influencing the timing and duration of the carbon uptake period especially in early spring and late autumn when trees are leafless. However, given the overwhelming influence of canopy trees on forest ecosystem functioning, shrubs are often ignored in ecosystem modeling. Isolating the shrub contribution to C flux or satellite-derived forest phenology is challenging. In addition, since shrubs are more likely to be invasive than trees, future changes to shrub species composition are likely, with consequent implications for both over- and understory species composition and ecosystem functioning. Surprisingly, given their multifaceted role, our review revealed that studies on temperate deciduous shrub phenology are limited with the majority focusing on managing invasive shrubs in USA forests. In addition, results of some studies using a large number of species from a range of geographical locations suggested that, in general, invasive shrubs leafed out earlier and retained leaves longer than native species. However, this may not be directly applicable to local conditions with a smaller range of locally adapted species. Therefore, in order to fully understand the role of shrub phenology in temperate deciduous forests, in terms of invasive species, response to climate change and subsequent influence on C balance it will be necessary to establish phenological monitoring sites in which both tree and shrub phenology are recorded concurrently across a range of geographical locations.

Integrating Causal and Evolutionary Analysis of Life-History Evolution: Arrival Date in a Long-Distant Migrant

In migratory species, the timing of arrival at the breeding grounds is a life-history trait with major fitness consequences. The optimal arrival date varies from year-to-year, and animals use cues to adjust their arrival dates to match this annual variation. However, which cues they use to time their arrival and whether these cues actually predict the annual optimal arrival date is largely unknown. Here, we integrate causal and evolutionary analysis by identifying the environmental variables used by a migratory songbird to time its arrival dates and testing whether these environmental variables also predicted the optimal time to arrive. We used 11 years of male arrival data of a pied flycatcher population. Specifically, we tested whether temperature and normalized difference vegetation index (NDVI) values from their breeding grounds in the Netherlands and from their wintering grounds in Ivory Coast explained the variation in arrival date, and whether these variables correlated with the position of the annual fitness peak at the breeding grounds. We found that temperature and NDVI, both from the wintering and the breeding grounds, explained the annual variation in arrival date, but did not correlate with the optimal arrival date. We explore three alternative explanations for this lack of correlation. Firstly, the date of the fitness peak may have been incorrectly estimated because a potentially important component of fitness (i.e., migration date dependent mortality en route or directly upon arrival) could not be measured. Secondly, we focused on male timing but the fitness landscape is also likely to be shaped by female timing. Finally, the correlation has recently disappeared because climate change disrupted the predictive value of the cues that the birds use to time their migration. In the latter case, birds may adapt by altering their sensitivity to temperature and NDVI.

Tracking snowmelt to jump the green wave: phenological drivers of migration in a northern ungulate

In northern climates, spring is a time of rapid environmental change: for migrating terrestrial animals, melting snow facilitates foraging and travel, and newly emergent vegetation provides a valuable nutritional resource. These changes result in selection on the timing of important life-history events such as migration and parturition occurring when high-quality resources are most abundant. We examined the timing of female caribou (Rangifer tarandus, n = 94) migration and parturition in five herds across 7 yr in Newfoundland, Canada, as a function of two measures of environmental change-snowmelt and vegetation green-up. We generated resource selection functions to test whether caribou selected for areas associated with snowmelt and green-up during migration and following calving. We found that caribou migrated approximately 1 wk prior to snowmelt, with the flush of emergent vegetation occurring during the weeks following parturition. The results indicate that caribou "jump" the green wave of emergent forage and do so by tracking the receding edge of melting snow, likely reducing movement and foraging costs related to snow cover. Our research further broadens the ecological scope of resource tracking in animals. We demonstrate that resource tracking extends beyond resources directly related to foraging to those related to movement. We also show that snowmelt provides an environmental cue that may provide a buffer against changing environmental conditions.

Breeding at higher latitude is associated with higher photoperiodic threshold and delayed reproductive development in a songbird

Many seasonally breeding animals exhibit a threshold day length (critical photoperiod; CPP) for gonadal growth, and populations breeding at higher latitudes typically have a higher CPP. Much less is known about latitudinal variation in CPP in migratory population that winter away from their breeding range and must time their reproduction to match favorable conditions at their destination. To address the relationship between migration, breeding latitude, and CPP, we held two closely related songbird populations in a common environment. One population is resident (Junco hyemalis carolinensis), the other winters in sympatry with the residents but migrates north to breed (Junco hyemalis hyemalis). We gradually increased photoperiod and measured indices of readiness to migrate (fat score, body mass) and breed (cloacal protuberance volume, baseline testosterone, and gonadotropin releasing hormone challenged testosterone). To estimate breeding latitude, we measured hydrogen isotopes in feathers grown the preceding year. As we predicted, we found a higher CPP in migrants than residents, and a higher CPP among migrants deriving from higher as opposed to lower latitudes. Migrants also terminated breeding earlier than residents, indicating a shorter breeding season. To our knowledge, this is a first demonstration of latitudinal variation in CPP-dependent reproductive timing in bird populations that co-exist in the non-breeding season but breed at different latitudes. We conclude that bird populations appear to exhibit local adaptation in reproductive timing by relying on differential CPP response that is predictive of future conditions on the breeding ground.

No evidence for fitness signatures consistent with increasing trophic mismatch over 30 years in a population of European shag Phalacrocorax aristotelis

As temperatures rise, timing of reproduction is changing at different rates across trophic levels, potentially resulting in asynchrony between consumers and their resources. The match-mismatch hypothesis (MMH) suggests that trophic asynchrony will have negative impacts on average productivity of consumers. It is also thought to lead to selection on timing of breeding, as the most asynchronous individuals will show the greatest reductions in fitness. Using a 30-year individual-level dataset of breeding phenology and success from a population of European shags on the Isle of May, Scotland, we tested a series of predictions consistent with the hypothesis that fitness impacts of trophic asynchrony are increasing. These predictions quantified changes in average annual breeding success and strength of selection on timing of breeding, over time and in relation to rising sea surface temperature (SST) and diet composition. Annual average (population) breeding success was negatively correlated with average lay date yet showed no trend over time, or in relation to increasing SST or the proportion of principal prey in the diet, as would be expected if trophic mismatch was increasing. At the individual level, we found evidence for stabilising selection and directional selection for earlier breeding, although the earliest birds were not the most productive. However, selection for earlier laying did not strengthen over time, or in relation to SST or slope of the seasonal shift in diet from principal to secondary prey. We found that the optimum lay date advanced by almost 4 weeks during the study, and that the population mean lay date tracked this shift. Our results indicate that average performance correlates with absolute timing of breeding of the population, and there is selection for earlier laying at the individual level. However, we found no fitness signatures of a change in the impact of climate-induced trophic mismatch, and evidence that shags are tracking long-term shifts in optimum timing. This suggests that if asynchrony is present in this system, breeding success is not impacted. Our approach highlights the advantages of examining variation at both population and individual levels when assessing evidence for fitness impacts of trophic asynchrony.

Phenological Response in the Trophic Levels to Climate Change in Korea

The response of the phenological events of individual species to climate change is not isolated, but is connected through interaction with other species at the same or adjacent trophic level. Using long-term phenological data observed since 1976 in Korea, whose temperature has risen more steeply than the average global temperature, this study conducted phenological analysis (differ-ences in the phenology of groups, differences in phenological shifts due to climate change, differ-ences in phenological sensitivity to climate by groups, and the change of phenological day differ-ences among interacting groups). The phenological shift of the producer group (plants) was found to be negative in all researched species, which means that it blooms quickly over the years. The regression slope of consumers (primary consumers and secondary consumers) was generally posi-tive which means that the phenological events of these species tended to be later during the study period. The inter-regional deviation of phenological events was not large for any plant except for plum tree and Black locust. In addition, regional variations in high trophic levels of secondary consumers tended to be greater than that of producers and primary consumers. Among the studied species, plum was the most sensitive to temperature, and when the temperature rose by 1 °C, the flowering time of plum decreased by 7.20 days. As a result of checking the day differences in the phenological events of the interacting species, the phenological events of species were reversed, and butterflies have appeared earlier than plum, Korean forsythia, and Korean rosebay since 1990. Using long-term data from Korea, this study investigated differences in phenological reactions among trophic groups. There is a possibility of a phenological mismatch between trophic groups in the future if global warming continues due to differences in sensitivity to climate and phenological shifts between trophic levels.

Climate and weather have differential effects in a high latitude passerine community

Climatic factors act on populations at multiple timescales leading to the separation of long-term climate and shorter-term weather effects. We used passerine counts from 1995 to 2019 in subarctic Alaska (Denali National Park, USA) to assess the impacts of the prior breeding season's weather on breeding season abundance and the impacts of climate measured through shifts in elevational distribution. Weather and climate appear to have had opposing effects on the abundance of some shrub-associated species as evidenced by a positive response to nesting phase temperature over a 1-year lag and a negative response to warming-induced shifts in shrub-dominated habitats over the long term. The latter response was indicated by declines in abundance which occurred in some part through portions of these populations shifting upslope of our fixed sampling frame. Overall, the abundance of species was related to one or more of the lagged effects of weather and the effects of weather alone drove nearly twofold variation in annual abundance in most species. The effect of nesting phase temperature was a strong positive predictor at both community and individual species levels, whereas arrival phase temperature had weak support at both levels. The effects of total precipitation during the nesting phase and snowmelt timing shared mixed support at community and species levels, but generally indicated higher abundance following seasons that were drier and had earlier snowmelt. Together, our findings of opposing effects of climatic variables at different timescales have implications for understanding the mechanisms of population and distributional change in passerines in the subarctic.

Searching for synthetic mechanisms on how biological traits mediate species responses to climate change

Abstract: Climate change will likely be the most significant challenge faced by species in this century, and species’ ability to cope with climate change depends on their life history and ecological and evolutionary traits. Understanding how these traits mediate species’ responses is beneficial for identifying more vulnerable species or prone to extinction risk. Here, we carried out a literature review describing how four traits commonly used in vulnerability assessments (i.e. clutch size, diet breadth, dispersal ability, and climatic tolerance) may determine species vulnerability. We also portray the possible mechanisms that explain how these traits govern species responses to climate change. The literature suggests different mechanisms operating for the evaluated traits. The mechanism of response to climate change differs between species inhabiting tropical and temperate regions: while species from the temperate areas may respond positively to temperature rise, tropical species may be severely affected. Since ectotherms depend on environment temperature, they are more sensitive and present different response mechanisms from endotherms.

Environment-induced changes in reproductive strategies and their transgenerational effects in the three-spined stickleback

An organism may increase its fitness by changing its reproductive strategies in response to environmental cues, but the possible consequences of those changes for the next generation have rarely been explored. By using an experiment on the three-spined stickleback (Gasterosteus aculeatus), we studied how changes in the onset of breeding photoperiod (early versus late) affect reproductive strategies of males and females, and life histories of their offspring. We also explored whether telomeres are involved in the within- and transgenerational effects. In response to the late onset of breeding photoperiod, females reduced their investment in the early clutches, but males increased their investment in sexual signals. Costs of increased reproductive investment in terms of telomere loss were evident only in the late females. The environmentally induced changes in reproductive strategies affected offspring growth and survival. Most notably, offspring growth rate was the fastest when both parents experienced a delayed (i.e., late) breeding photoperiod, and survival rate was the highest when both parents experienced an advanced (i.e., early) breeding photoperiod. There was no evidence of transgenerational effects on offspring telomere length despite positive parents-offspring relationships in this trait. Our results highlight that environmental changes may impact more than one generation by altering reproductive strategies of seasonal breeders with consequences for offspring viability.

Body Size Variation in Italian Lesser Horseshoe Bats Rhinolophus hipposideros over 147 Years: Exploring the Effects of Climate Change, Urbanization and Geography

Body size in animals commonly shows geographic and temporal variations that may depend upon several environmental drivers, including climatic conditions, productivity, geography and species interactions. The topic of body size trends across time has gained momentum in recent years since this has been proposed as a third universal response to climate change along with changes in distribution and phenology. However, disentangling the genuine effects of climate change from those of other environmental factors is often far from trivial. In this study, we tested a set of hypotheses concerning body size variation across time and space in Italian populations of a rhinolophid bat, the lesser horseshoe bat Rhinolophus hipposideros. We examined forearm length (FAL) and cranial linear traits in a unique historical collection of this species covering years from 1869 to 2016, representing, to the best of our knowledge, the longest time series ever considered in a morphological assessment of a bat species. No temporal changes occurred, rejecting the hypotheses that body size varied in response to climate change or urbanization (light pollution). We found that FAL increased with latitude following a Bergmann's rule trend, whereas the width of upper incisors, likely a diet-related trait, showed an opposite pattern which awaits explanation. We also confirmed that FAL is sexually dimorphic in this species and ruled out that insularity has any detectable effect on the linear traits we considered. This suggests that positive responses of body size to latitude do not mean per se that concurring temporal responses to climate change are also expected. Further investigations should explore the occurrence of these patterns over larger spatial scales and more species in order to detect the existence of general patterns across time and space.

Differences in spatial versus temporal reaction norms for spring and autumn phenological events

To do the right thing at the right time, organisms need to glean cues from their environment. How they respond can then be described by reaction norms, i.e., by the relationship between the phenotype expressed (the phenology of an event) and the environment (the date when a given number of degree-days are achieved). We use information on 178 phenological events across the former Soviet Union. We found the timing of events to differ more between sites in spring and less in autumn. These patterns of local adaptation translate to a massive imprint on nature’s calendar: geographic variation in phenology is more pronounced in spring and less pronounced in autumn than if organisms were to respond equally everywhere.

For species to stay temporally tuned to their environment, they use cues such as the accumulation of degree-days. The relationships between the timing of a phenological event in a population and its environmental cue can be described by a population-level reaction norm. Variation in reaction norms along environmental gradients may either intensify the environmental effects on timing (cogradient variation) or attenuate the effects (countergradient variation). To resolve spatial and seasonal variation in species’ response, we use a unique dataset of 91 taxa and 178 phenological events observed across a network of 472 monitoring sites, spread across the nations of the former Soviet Union. We show that compared to local rates of advancement of phenological events with the advancement of temperature-related cues (i.e., variation within site over years), spatial variation in reaction norms tend to accentuate responses in spring (cogradient variation) and attenuate them in autumn (countergradient variation). As a result, among-population variation in the timing of events is greater in spring and less in autumn than if all populations followed the same reaction norm regardless of location. Despite such signs of local adaptation, overall phenotypic plasticity was not sufficient for phenological events to keep exact pace with their cues—the earlier the year, the more did the timing of the phenological event lag behind the timing of the cue. Overall, these patterns suggest that differences in the spatial versus temporal reaction norms will affect species’ response to climate change in opposite ways in spring and autumn.

Density-Dependent Adaptive Topography in a Small Passerine Bird, the Collared Flycatcher

AbstractAdaptive topography is a central concept in evolutionary biology, describing how the mean fitness of a population changes with gene frequencies or mean phenotypes. We use expected population size as a quantity to be maximized by natural selection to show that selection on pairwise combinations of reproductive traits of collared flycatchers caused by fluctuations in population size generated an adaptive topography with distinct peaks often located at intermediate phenotypes. This occurred because r- and K-selection made phenotypes favored at small densities different from those with higher fitness at population sizes close to the carrying capacity K. Fitness decreased rapidly with a delay in the timing of egg laying, with a density-dependent effect especially occurring among early-laying females. The number of fledglings maximizing fitness was larger at small population sizes than when close to K. Finally, there was directional selection for large fledglings independent of population size. We suggest that these patterns can be explained by increased competition for some limiting resources or access to favorable nest sites at high population densities. Thus, r- and K-selection based on expected population size as an evolutionary maximization criterion may influence life-history evolution and constrain the selective responses to changes in the environment.

Warmer April Temperatures on Breeding Grounds Promote Earlier Nesting in a Long-Distance Migratory Bird, the Prothonotary Warbler

Global climate change and warming are altering hemispheric and local weather patterns. Altered weather patterns have great potential to affect the phenology of life history events, such as the initiation of breeding in organisms that reproduce seasonally. Long-distance migratory birds may be particularly challenged by changes in local weather on breeding grounds because they arrive from distant locations and must commence breeding when conditions are appropriate. Here we explore the effects of local temperature on first egg dates and annual productivity in a long-distance Neotropical migratory songbird, the prothonotary warbler Protonotaria citrea. We present results from a 20-year (1994 to 2013) study documenting the detailed nesting activities of a color-marked population (average of 155 individual females each year) of warblers in southern Illinois, United States. The warblers typically arrive in April and start breeding in late April and May in our study system. We tested for an effect of local average April daily temperature and female age on first egg dates, total number of offspring produced per female, and the probability of fledging two broods. We found that warmer April temperatures promoted earlier first egg dates and higher average annual productivity in the warblers. On average, older females had earlier first egg dates than 1-year-old females, but both age groups responded similarly to local April temperatures. The reproductive gains associated with earlier first egg dates in warmer years stemmed from an increased probability of successfully fledging two broods, suggesting that earlier first egg dates do not currently create a mismatch with food (insect) resources. Earliest arrival dates of warblers to the region of our study system were not affected by local April temperatures, suggesting that females vary their first egg date based on conditions they experience/assess after their arrival. Whereas these birds currently adjust the timing of their breeding and actually produce more offspring in warmer years, continued global warming may eventually upset the current balance between arrival dates, food resources, and the commencement of nesting.

Increased Stopover Duration and Low Body Condition of the Pied Flycatcher (Ficedula hypoleuca) at an Autumn Stopover Site

Simple Summary

Many bird species that migrate long distances are in decline partly because of environmental changes, such as climate change or land-use changes. Although much is already known on the effects of environmental change on birds that are on their spring migration or on their breeding grounds, little is known with regard to possible negative effects on birds that are on their autumn migration and visiting so-called stopover sites on their way to their wintering grounds. These stopover sites are vital for birds to refuel, and a potential deteriorating quality of the stopover sites may lead to individuals dying during migration. We investigated the impacts of local environmental conditions on the migration strategy and body condition of the Pied Flycatcher at an autumn migration stopover site using long-term ringing data and local environmental conditions. We found that although birds arrived and departed the stopover site around the same time over the years, the body condition of the individuals caught decreased, and the length of their stay at the stopover site increased. This suggests that conditions at the stopover site during the autumn migration period have deteriorated over time which may lead to the death of more birds during autumn migration.

Abstract

Many long-distance migratory bird species are in decline, of which environmental changes, such as climate change and land-use changes, are thought to be important drivers. The effects of environmental change on the migration of these birds have often been studied during spring migration. Fewer studies have explored the impacts of environmental change on autumn migration, especially at stopover sites. However, stopover sites are important, as the quality of these sites is expected to change over time. We investigated impacts of local environmental conditions on the migration strategy and body condition of the Pied Flycatcher (Ficedula hypoleuca) at an autumn migration stopover site using long-term ringing data (1996–2018) and local environmental conditions. We found that although the arrival and departure dates of birds at the stopover site remained unchanged, the body condition (fat score) of the individuals caught decreased, and the stopover duration increased. This suggests that conditions at the stopover site during the autumn migration period have deteriorated over time. This study emphasizes the importance of suitable stopover sites for migratory birds and stresses that changes in environmental conditions during the autumn migration period may be contributing to the current decline in long-distance migratory passerines.

Sensory pollutants alter bird phenology and fitness across a continent

Expansion of anthropogenic noise and night lighting across our planet^1,2 is of increasing conservation concern^3-6. Despite growing knowledge of physiological and behavioural responses to these stimuli from single-species and local-scale studies, whether these pollutants affect fitness is less clear, as is how and why species vary in their sensitivity to these anthropic stressors. Here we leverage a large citizen science dataset paired with high-resolution noise and light data from across the contiguous United States to assess how these stimuli affect reproductive success in 142 bird species. We find responses to both sensory pollutants linked to the functional traits and habitat affiliations of species. For example, overall nest success was negatively correlated with noise among birds in closed environments. Species-specific changes in reproductive timing and hatching success in response to noise exposure were explained by vocalization frequency, nesting location and diet. Additionally, increased light-gathering ability of species' eyes was associated with stronger advancements in reproductive timing in response to light exposure, potentially creating phenological mismatches⁷. Unexpectedly, better light-gathering ability was linked to reduced clutch failure and increased overall nest success in response to light exposure, raising important questions about how responses to sensory pollutants counteract or exacerbate responses to other aspects of global change, such as climate warming. These findings demonstrate that anthropogenic noise and light can substantially affect breeding bird phenology and fitness, and underscore the need to consider sensory pollutants alongside traditional dimensions of the environment that typically inform biodiversity conservation.

Prediction of Plant Phenological Shift under Climate Change in South Korea

Information on the phenological shift of plants can be used to detect climate change and predict changes in the ecosystem. In this study, the changes in first flowering dates (FFDs) of the plum tree (Prunus mume), Korean forsythia (Forsythia koreana), Korean rosebay (Rhododendron mucronulatum), cherry tree (Prunus yedoensis), and peach tree (Prunus persica) in Korea during 1920–2019 were investigated. In addition, the changes in the climatic factors (temperature and precipitation) and their relationship with the FFDs were analyzed. The changes in the temperature and precipitation during the January–February–March period and the phenological shifts of all research species during 1920–2019 indicate that warm and dry spring weather advances the FFDs. Moreover, the temperature has a greater impact on this phenological shift than precipitation. Earlier flowering species are more likely to advance their FFDs than later flowering species. Hence, the temporal asynchrony among plant species will become worse with climate change. In addition, the FFDs in 2100 were predicted based on representative concentration pathway (RCP) scenarios. The difference between the predicted FFDs of the RCP 4.5 and RCP 6.0 for 2100 was significant; the effectiveness of greenhouse gas policies will presumably determine the degree of the plant phenological shift in the future. Furthermore, we presented the predicted FFDs for 2100.

The effect of climate change on laying dates, clutch size and productivity of Eurasian Coots Fulica atra

Climate change is affecting many living organisms; however, the responses of many of them remain unknown. In this paper, we present the results regarding the response of a bird species from the rallid family to the increased temperatures during the breeding season. We analysed the breeding data of Eurasian Coots nesting during 30 seasons between 1972 and 2019. During the study period, mean temperatures in April, the month when Coots start nesting, increased by 3.5 °C, and in months corresponding with the species breeding season by 2.6 °C. Breeding Coots advanced their earliest and median laying dates across the study period; however, the duration of their breeding season remained unchanged. We did not detect any significant temporal changes in clutch size, but clutches have become much more variable in size throughout the study period. Nest failures and production of offspring per nest did not change over the study period; however, the production of young per successful nest significantly declined. It is likely that this decline is the effect of mismatch between the period of food abundance (dipterans collected from water), and hatchling emergence, which is advanced due to change in climate. Future studies investigating the occurrence of dipteran resources at water bodies are needed to test this hypothesis.

Surface temperatures of non-incubated eggs in great tits (Parus major) are strongly associated with ambient temperature

Temperature is one of the best investigated environmental factors in ecological life-history studies and is increasingly considered in the contexts of climate change and urbanization. In avian ecology, few studies have examined the associations between thermal dynamics in the nest environment and its neighbouring air. Here, we placed avian nests and non-incubated eggs inside nest boxes at various air temperatures that ranged from 0.3 to 33.1 °C, both in the field and in laboratory conditions. We measured how the design of the boxes, their compass orientation and their location in more or less urbanized environments affected the surface temperature of nests and eggs. We also assessed whether covering the eggs with lining material influenced their surface temperature. Overall, across all performed tests, we found that the surface temperature of nests and eggs strongly reflected the air temperature measured outside of the nest boxes. While the design of the nest boxes had little influence on the temperature of nests and eggs, orienting the nest boxes to the north or to the west significantly decreased their surface temperature. The presence of lining material also kept eggs slightly warmer when air temperatures were low. Altogether these results suggest that non-incubated eggs are not well protected against extreme air temperatures prior to the onset of incubation. From an evolutionary point of view, producers of ectotherm eggs need therefore to time egg-laying appropriately in order to avoid unfavourable thermal nest environments.