Dynamic sensitivity to resource availability influences population responses to mismatches in a shorebird

Climate change has caused shifts in seasonally recurring biological events leading to the temporal decoupling of consumer-resource pairs - i.e., phenological mismatching. Although mismatches often affect individual fitness, they do not invariably scale up to affect populations, making it difficult to assess the risk they pose. Individual variation may contribute to this inconsistency, with changes in resource availability and consumer needs leading mismatches to have different outcomes over time. Nevertheless, most models estimate a consumer's match from a single timepoint, potentially obscuring when mismatches matter to populations. We analyzed how the effects of mismatches varied over time by studying precocial Hudsonian godwit (Limosa haemastica) chicks and their invertebrate prey from 2009 to 2019. We developed individual and population level models to determine how age-specific variation affect the relationship between godwits and resource availability. We found that periods with abundant resources led to higher growth and survival of godwit chicks, but also that chick survival was increasingly related to the availability of larger prey as chicks aged. At the population level, estimates of mismatches using age-structured consumer demand explained more variation in annual godwit fledging rates than more commonly used alternatives. Our study suggests that modeling the effects of mismatches as the disrupted interaction between dynamic consumer needs and resource availability clarifies when mismatches matter to both individuals and populations.

Climate change and lithium mining influence flamingo abundance in the Lithium Triangle

The development of technologies to slow climate change has been identified as a global imperative. Nonetheless, such 'green' technologies can potentially have negative impacts on biodiversity. We explored how climate change and the mining of lithium for green technologies influence surface water availability, primary productivity and the abundance of three threatened and economically important flamingo species in the 'Lithium Triangle' of the Chilean Andes. We combined climate and primary productivity data with remotely sensed measures of surface water levels and a 30-year dataset on flamingo abundance using structural equation modelling. We found that, regionally, flamingo abundance fluctuated dramatically from year-to-year in response to variation in surface water levels and primary productivity but did not exhibit any temporal trends. Locally, in the Salar de Atacama-where lithium mining is focused-we found that mining was negatively correlated with the abundance of two of the three flamingo species. These results suggest continued increases in lithium mining and declines in surface water could soon have dramatic effects on flamingo abundance across their range. Efforts to slow the expansion of mining and the impacts of climate change are, therefore, urgently needed to benefit local biodiversity and the local human economy that depends on it.

Compensation for wind drift prevails for a shorebird on a long-distance, transoceanic flight

BACKGROUND

Conditions encountered en route can dramatically impact the energy that migratory species spend on movement. Migratory birds often manage energetic costs by adjusting their behavior in relation to wind conditions as they fly. Wind-influenced behaviors can offer insight into the relative importance of risk and resistance during migration, but to date, they have only been studied in a limited subset of avian species and flight types. We add to this understanding by examining in-flight behaviors over a days-long, barrier-crossing flight in a migratory shorebird.

METHODS

Using satellite tracking devices, we followed 25 Hudsonian godwits (Limosa haemastica) from 2019-2021 as they migrated northward across a largely transoceanic landscape extending > 7000 km from Chiloé Island, Chile to the northern coast of the Gulf of Mexico. We identified in-flight behaviors during this crossing by comparing directions of critical movement vectors and used mixed models to test whether the resulting patterns supported three classical predictions about wind and migration.

RESULTS

Contrary to our predictions, compensation did not increase linearly with distance traveled, was not constrained during flight over open ocean, and did not influence where an individual ultimately crossed over the northern coast of the Gulf of Mexico at the end of this flight. Instead, we found a strong preference for full compensation throughout godwit flight paths.

CONCLUSIONS

Our results indicate that compensation is crucial to godwits, emphasizing the role of risk in shaping migratory behavior and raising questions about the consequences of changing wind regimes for other barrier-crossing aerial migrants.

Behavioural adjustments in the social associations of a precocial shorebird mediate the costs and benefits of grouping decisions

Animals weigh multiple costs and benefits when making grouping decisions. The cost‐avoidance grouping framework proposes that group density, information quality and risk affect an individual’s preference for con or heterospecific groups. However, this assumes the cost–benefit balance of a particular grouping is constant spatiotemporally, which may not always be true. Investigating how spatiotemporal context influences grouping choices is therefore key to understanding how animals contend with changing conditions.

Changes in body size during development lead to variable conditions for individuals over short time‐scales that can influence their ecological interactions. Hudsonian godwits Limosa haemastica, for instance, form a protective nesting association with a major predator of young godwit chicks, colonial short‐billed gulls Larus brachyrhynchus. Godwit broods may avoid areas of higher gull densities when chicks are susceptible to gull predation but likely experience higher risk from alternative predators as a result. Associating with conspecifics could allow godwits to buffer these costs but requires enough other broods with whom to group.

To determine how age‐dependent predation risk and conspecific density influence godwit grouping behaviours, we first quantified the time‐dependent effects of con‐ and heterospecific interactions on the mortality risk for godwit chicks throughout development. We then determined how godwit density and chick age affected their associations with con‐ and heterospecific.

We found that younger godwit chicks' survival improved with closer association with conspecifics, earlier hatch dates and lower gull densities, whereas older chicks survived better with earlier hatch dates, though this effect was less clear. Concomitantly, godwit broods avoided gulls early in development and when godwit densities were high but maintained loose associations with conspecifics throughout development.

We identified how individuals can optimally shift with whom they group according to risks that vary spatially and temporally. Investigating the effects of a species' ecological interactions across spatiotemporal contexts in this way can shed light on how animals adjust their associations according to the costs and benefits of each association.

Age-dependent timing and routes demonstrate developmental plasticity in a long-distance migratory bird

Longitudinal tracking studies have revealed consistent differences in the migration patterns of individuals from the same populations. The sources or processes causing this individual variation are largely unresolved. As a result, it is mostly unknown how much, how fast and when animals can adjust their migrations to changing environments.

We studied the ontogeny of migration in a long‐distance migratory shorebird, the black‐tailed godwit Limosa limosa limosa, a species known to exhibit marked individuality in the migratory routines of adults. By observing how and when these individual differences arise, we aimed to elucidate whether individual differences in migratory behaviour are inherited or emerge as a result of developmental plasticity.

We simultaneously tracked juvenile and adult godwits from the same breeding area on their south‐ and northward migrations. To determine how and when individual differences begin to arise, we related juvenile migration routes, timing and mortality rates to hatch date and hatch year. Then, we compared adult and juvenile migration patterns to identify potential age‐dependent differences.

In juveniles, the timing of their first southward departure was related to hatch date. However, their subsequent migration routes, orientation, destination, migratory duration and likelihood of mortality were unrelated to the year or timing of migration, or their sex. Juveniles left the Netherlands after all tracked adults. They then flew non‐stop to West Africa more often and incurred higher mortality rates than adults. Some juveniles also took routes and visited stopover sites far outside the well‐documented adult migratory corridor. Such juveniles, however, were not more likely to die.

We found that juveniles exhibited different migratory patterns than adults, but no evidence that these behaviours are under natural selection. We thus eliminate the possibility that the individual differences observed among adult godwits are present at hatch or during their first migration. This adds to the mounting evidence that animals possess the developmental plasticity to change their migration later in life in response to environmental conditions as those conditions are experienced.

Broad Concordance in the Spatial Distribution of Adaptive and Neutral Genetic Variation across an Elevational Gradient in Deer Mice

When species are continuously distributed across environmental gradients, the relative strength of selection and gene flow shape spatial patterns of genetic variation, potentially leading to variable levels of differentiation across loci. Determining whether adaptive genetic variation tends to be structured differently than neutral variation along environmental gradients is an open and important question in evolutionary genetics. We performed exome-wide population genomic analysis on deer mice sampled along an elevational gradient of nearly 4,000 m of vertical relief. Using a combination of selection scans, genotype-environment associations, and geographic cline analyses, we found that a large proportion of the exome has experienced a history of altitude-related selection. Elevational clines for nearly 30% of these putatively adaptive loci were shifted significantly up- or downslope of clines for loci that did not bear similar signatures of selection. Many of these selection targets can be plausibly linked to known phenotypic differences between highland and lowland deer mice, although the vast majority of these candidates have not been reported in other studies of highland taxa. Together, these results suggest new hypotheses about the genetic basis of physiological adaptation to high altitude, and the spatial distribution of adaptive genetic variation along environmental gradients.

Interspecific aggression in sympatry between congeneric tropical birds

Interspecific aggression may shape species distributions through competitive exclusion, resulting in spatial segregation, or facilitate sympatry as an adaptive mechanism for resource partitioning. Competitive exclusion results from asymmetric aggression of one species towards another, but if the aggressive relationship between species is symmetric, they may persist in sympatry. Interspecific aggression is widely cited as a mechanism for maintaining the distributional limits of tropical birds, but how it shapes the spatial dynamics of competing species that are sympatric over larger geographic areas is less clear. To address this issue, we conducted reciprocal playback experiments on two congeneric Antbirds — Thamnophilus atrinucha and T. doliatus — that occur in sympatry across a habitat matrix in Colombia to characterize their relationship as symmetrically or asymmetrically aggressive and analyzed point count data to assess the degree to which they occur sympatrically. We found weak evidence for competitive exclusion, with the larger T. doliatus responding asymmetrically to T. atrinucha, and the two species having a low co-detection rate during point counts. However, despite their 22% difference in body size, T. atrinucha still responded to T. doliatus playback in over half of our trials, and the two species co-occurred on nearly 25% of point counts, indicating that interspecific aggression does not drive complete spatial segregation. Our findings highlight how the degree to which one species can competitively exclude another may vary, especially across a dynamic landscape.

Body temperature maintenance acclimates in a winter-tenacious songbird

Flexibility in heat generation and dissipation mechanisms provides endotherms the ability to match their thermoregulatory strategy with external demands. However, the degree to which these two mechanisms account for seasonal changes in body temperature regulation is little explored. Here, we present novel data on the regulation of avian body temperature to investigate how birds alter mechanisms of heat production and heat conservation to deal with variation in ambient conditions. We subjected dark-eyed juncos (Junco hyemalis) to chronic cold acclimations of varying duration and subsequently quantified their metabolic rates, thermal conductance and ability to maintain normothermia. Cold-acclimated birds adjusted traits related to both heat generation (increased summit metabolic rate) and heat conservation (decreased conductance) to improve their body temperature regulation. Increases in summit metabolic rate occurred rapidly, but plateaued after 1 week of cold exposure. In contrast, changes to conductance occurred only after 9 weeks of cold exposure. Thus, the ability to maintain body temperature continued to improve throughout the experiment, but the mechanisms underlying this improvement changed through time. Our results demonstrate the ability of birds to adjust thermoregulatory strategies in response to thermal cues and reveal that birds may combine multiple responses to meet the specific demands of their environments.

Seasonal survival and reversible state effects in a long-distance migratory shorebird

Events during one stage of the annual cycle can reversibly affect an individual's condition and performance not only within that stage, but also in subsequent stages (i.e. reversible state effects). Despite strong conceptual links, however, few studies have been able to empirically link individual-level reversible state effects with larger-scale demographic processes. We studied both survival and potential reversible state effects in a long-distance migratory shorebird, the Hudsonian Godwit Limosa haemastica. Specifically, we estimated period-specific survival probabilities across the annual cycle and examined the extent to which an individual's body condition, foraging success and habitat quality during the nonbreeding season affected its subsequent survival and reproductive performance. Godwit survival rates were high throughout the annual cycle, but lowest during the breeding season, only slightly higher during southbound migration and highest during the stationary nonbreeding season. Our results indicate that overwintering godwits foraging in high-quality habitats had comparably better nutritional status and pre-migratory body condition, which in turn improved their return rates and the likelihood that their nests and chicks survived during the subsequent breeding season. Reversible state effects thus appeared to link events between nonbreeding and breeding seasons via an individual's condition, in turn affecting their survival and subsequent reproductive performance. Our study thus provides one of the few empirical demonstrations of theoretical predictions that reversible state effects have the potential to influence population dynamics.

Adverse wind conditions during northward Sahara crossings increase the in-flight mortality of Black-tailed Godwits

Long‐distance migratory flights are predicted to be associated with higher mortality rates when individuals encounter adverse weather conditions. However, directly connecting environmental conditions experienced in‐flight with the survival of migrants has proven difficult. We studied how the in‐flight mortality of 53 satellite‐tagged Black‐tailed Godwits (Limosa limosa limosa) during 132 crossings of the Sahara Desert, a major geographical barrier along their migration route between The Netherlands and sub‐Saharan Africa, is correlated with the experienced wind conditions and departure date during both southward and northward migration. We show that godwits experienced higher wind assistance during southward crossings, which seems to reflect local prevailing trade winds. Critically, we found that fatal northward crossings (15 deaths during 61 crossings) were associated with adverse wind conditions. Wind conditions during migration can thus directly influence vital rates. Changing wind conditions associated with global change may thus profoundly influence the costs of long‐distance migration in the future.

Comment on "Global pattern of nest predation is disrupted by climate change in shorebirds"

Kubelka et al (Reports, 9 November 2018, p. 680) claim that climate change has disrupted patterns of nest predation in shorebirds. They report that predation rates have increased since the 1950s, especially in the Arctic. We describe methodological problems with their analyses and argue that there is no solid statistical support for their claims.

Natal habitat and sex-specific survival rates result in a male-biased adult sex ratio

The adult sex ratio (ASR) is a crucial component of the ecological and evolutionary forces shaping the dynamics of a population. Although in many declining populations ASRs have been reported to be skewed, empirical studies exploring the demographic factors shaping ASRs are still rare. In this study of the socially monogamous and sexually dimorphic Black-tailed Godwit (Limosa limosa limosa), we aim to evaluate the sex ratio of chicks at hatch and the subsequent sex-specific survival differences occurring over 3 subsequent life stages. We found that, at hatch, the sex ratio did not deviate from parity. However, the survival of pre-fledged females was 15-30% lower than that of males and the sex bias in survival was higher in low-quality habitat. Additionally, survival of adult females was almost 5% lower than that of adult males. Because survival rates of males and females did not differ during other life-history stages, the ASR in the population was biased toward males. Because females are larger than males, food limitations during development or sex-specific differences in the duration of development may explain the lower survival of female chicks. Differences among adults are less obvious and suggest previously unknown sex-related selection pressures. Irrespective of the underlying causes, by reducing the available number of females in this socially monogamous species, a male-biased ASR is likely to contribute to the ongoing decline of the Dutch godwit population.

Generational shift in spring staging site use by a long-distance migratory bird

In response to environmental change, species have been observed altering their migratory behaviours. Few studies, however, have been able to determine whether these alterations resulted from inherited, plastic or flexible changes. Here, we present a unique observation of a rapid population-level shift in migratory routes-over 300 km from Spain to Portugal-by continental black-tailed godwits Limosa limosa limosa This shift did not result from adult godwits changing staging sites, as adult site use was highly consistent. Rather, the shift resulted from young godwits predominantly using Portugal over Spain. We found no differences in reproductive success or survival among individuals using either staging site, indicating that the shift resulted from developmental plasticity rather than natural selection. Our results therefore suggest that new migratory routes can develop within a generation and that young individuals may be the agents of such rapid changes.

High-altitude shorebird migration in the absence of topographical barriers: avoiding high air temperatures and searching for profitable winds

Nearly 20% of all bird species migrate between breeding and nonbreeding sites annually. Their migrations include storied feats of endurance and physiology, from non-stop trans-Pacific crossings to flights at the cruising altitudes of jetliners. Despite intense interest in these performances, there remains great uncertainty about which factors most directly influence bird behaviour during migratory flights. We used GPS trackers that measure an individual's altitude and wingbeat frequency to track the migration of black-tailed godwits (Limosa limosa) and identify the abiotic factors influencing their in-flight migratory behaviour. We found that godwits flew at altitudes above 5000 m during 21% of all migratory flights, and reached maximum flight altitudes of nearly 6000 m. The partial pressure of oxygen at these altitudes is less than 50% of that at sea level, yet these extremely high flights occurred in the absence of topographical barriers. Instead, they were associated with high air temperatures at lower altitudes and increasing wind support at higher altitudes. Our results therefore suggest that wind, temperature and topography all play a role in determining migratory behaviour, but that their relative importance is context dependent. Extremely high-altitude flights may thus not be especially rare, but they may only occur in very specific environmental contexts.

Wetland salinity induces sex-dependent carry-over effects on the individual performance of a long-distance migrant

Salinization is having a major impact on wetlands and its biota worldwide. Specifically, many migratory animals that rely on wetlands are increasingly exposed to elevated salinity on their nonbreeding grounds. Experimental evidence suggests that physiological challenges associated with increasing salinity may disrupt self-maintenance processes in these species. Nonetheless, the potential role of salinity as a driver of ecological carry-over effects remains unstudied. Here, we investigated the extent to which the use of saline wetlands during winter - inferred from feather stable isotope values - induces residual effects that carry over and influence physiological traits relevant to fitness in black-tailed godwits Limosa limosa limosa on their northward migration. Overwintering males and females were segregated by wetland salinity in West Africa, with females mostly occupying freshwater wetlands. The use of these wetlands along a gradient of salinities was associated with differences in immune responsiveness to phytohaemagglutinin and sized-corrected body mass in godwits staging in southern Europe during northward migration - 3,000 km from the nonbreeding grounds - but in males only. These findings provide a window onto the processes by which wetland salinity can induce carry-over effects and can help predict how migratory species should respond to future climate-induced increases in salinity.

An ontogenetic perspective on individual differences

Phenotypic differences among individuals can arise during any stage of life. Although several distinct processes underlying individual differences have been defined and studied (e.g. parental effects, senescence), we lack an explicit, unified perspective for understanding how these processes contribute separately and synergistically to observed variation in functional traits. We propose a conceptual framework based on a developmental view of life-history variation, linking each ontogenetic stage with the types of individual differences originating during that period. In our view, the salient differences among these types are encapsulated by three key criteria: timing of onset, when fitness consequences are realized, and potential for reversibility. To fill a critical gap in this framework, we formulate a new term to refer to individual differences generated during adulthood-reversible state effects. We define these as 'reversible changes in a functional trait resulting from life-history trade-offs during adulthood that affect fitness', highlighting how the adult phenotype can be repeatedly altered in response to environmental variation. Defining individual differences in terms of trade-offs allows explicit predictions regarding when and where fitness consequences should be expected. Moreover, viewing individual differences in a developmental context highlights how different processes can work in concert to shape phenotype and fitness, and lays a foundation for research linking individual differences to ecological and evolutionary theory.

When Siberia came to the Netherlands: the response of continental black-tailed godwits to a rare spring weather event

1. Extreme weather events have the potential to alter both short- and long-term population dynamics as well as community- and ecosystem-level function. Such events are rare and stochastic, making it difficult to fully document how organisms respond to them and predict the repercussions of similar events in the future. 2. To improve our understanding of the mechanisms by which short-term events can incur long-term consequences, we documented the behavioural responses and fitness consequences for a long-distance migratory bird, the continental black-tailed godwit Limosa limosa limosa, resulting from a spring snowstorm and three-week period of record low temperatures. 3. The event caused measurable responses at three spatial scales - continental, regional and local - including migratory delays (+19 days), reverse migrations (>90 km), elevated metabolic costs (+8·8% maintenance metabolic rate) and increased foraging rates (+37%). 4. There were few long-term fitness consequences, however, and subsequent breeding seasons instead witnessed high levels of reproductive success and little evidence of carry-over effects. 5. This suggests that populations with continued access to food, behavioural flexibility and time to dissipate the costs of the event can likely withstand the consequences of an extreme weather event. For populations constrained in one of these respects, though, extreme events may entail extreme ecological consequences.

An exception to the rule: carry-over effects do not accumulate in a long-distance migratory bird

Recent years have seen a growing consensus that events during one part of an animal's annual cycle can detrimentally affect its future fitness. Notably, migratory species have been shown to commonly display such carry-over effects, facing severe time constraints and physiological stresses that can influence events across seasons. However, to date, no study has examined a full annual cycle to determine when these carry-over effects arise and how long they persist within and across years. Understanding when carry-over effects are created and how they persist is critical to identifying those periods and geographic locations that constrain the annual cycle of a population and determining how selection is acting upon individuals throughout the entire year. Using three consecutive years of migration tracks and four consecutive years of breeding success data, we tested whether carry-over effects in the form of timing deviations during one migratory segment of the annual cycle represent fitness costs that persist or accumulate across the annual cycle for a long-distance migratory bird, the Hudsonian godwit, Limosa haemastica. We found that individual godwits could migrate progressively later than population mean over the course of an entire migration period, especially southbound migration, but that these deviations did not accumulate across the entire year and were not consistently detected among individuals across years. Furthermore, neither the accumulation of lateness during previous portions of the annual cycle nor arrival date at the breeding grounds resulted in individuals suffering reductions in their breeding success or survival. Given their extreme life history, such a lack of carry-over effects suggests that strong selection exists on godwits at each stage of the annual cycle and that carry-over effects may not be able to persist in such a system, but also emphasizes that high-quality stopover and wintering sites are critical to the maintenance of long-distance migratory populations.