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

Responses in the breeding parameters of the collared flycatcher to the changing climate

Global climate change involves various aspects of climate, including precipitation changes and declining surface wind speeds, but studies investigating biological responses have often focused on the impacts of rising temperatures. Additionally, related long-term studies on bird reproduction tend to concentrate on breeding onset, even though other aspects of breeding could also be sensitive to the diverse weather aspects. This study aimed to explore how multiple aspects of breeding (breeding onset, hatching delay, breeding season length, clutch size, fledgling number) were associated with different weather components. We used an almost four-decade-long dataset to investigate the various aspects of breeding parameters of a collared flycatcher (Ficedula albicollis) population in the Carpathian Basin. Analyses revealed some considerable associations, for example, breeding seasons lengthened with the amount of daily precipitation, and clutch size increased with the number of cool days. Parallel and opposing changes in the correlated pairs of breeding and weather parameters were also observed. The phenological mismatch between prey availability and breeding time slightly increased, and fledgling number strongly decreased with increasing mistiming. Our results highlighted the intricate interplay between climate change and the reproductive patterns of migratory birds, emphasizing the need for a holistic approach. The results also underscored the potential threats posed by climate change to bird populations and the importance of adaptive responses to changing environmental conditions.

The Effects of Climate Change on the Nesting Phenology of Three Shorebird Species in the United States

Previous research suggests that a frequent response of organisms to the ongoing climate crisis is the adjustment of their reproductive timing or breeding phenology. Shorebirds may be especially vulnerable to increasing temperatures and precipitation, as many are migratory and depend on coastal habitats for wintering and breeding. These particular habitats could be at risk due to changes in climate, and nesting times often depend on food availability, which is often directly influenced by temperature. We investigated if clutch initiation dates (CID) for three shorebird species in the United States have become earlier over time with increasing temperatures and precipitation. We used nest records from Cornell's NestWatch program and various museum databases and weather station data from the National Oceanic and Atmospheric Administration. We found evidence that CIDs have become earlier over time, though this was only a significant factor for one species. While temperature in our study areas has increased significantly over time, precipitation changes were more variable and not always significantly predicted by time. We found evidence that one species may be responding to increasing temperatures by nesting earlier, but there was no support for our hypothesis that CID has changed due to changes in precipitation for any species. Results varied for each species, indicating the importance of further studies on shorebirds as the effects of climate change on their nesting phenology may not be fully realized and will likely depend on the species' biology and distribution.

Effects of meteorological conditions on brood care in cooperatively breeding carrion crow and consequences on reproductive success

Meteorological stressors (e.g., temperature and rain shortage) constrain brood provisioning in some bird species, but the consequences on reproductive success have been rarely quantified. Here we show, in a cooperatively breeding population of carrion crow Corvus corone in Spain, that individual feeding rates decreased significantly with rising air temperatures both in breeders and helpers, while lack of rain was associated with a significant reduction in the effort of the male helpers as compared to the other social categories. Group coordination, measured as the degree of alternation of nest visits by carers, was also negatively affected by rising temperature. Furthermore, we found that the body condition of the nestlings worsened when temperatures were high during the rearing period. Interestingly, the analysis of a long-term data set on crow reproduction showed that nestling body condition steadily deteriorated over the last 26-years. Although many factors may concur in causing population changes, our data suggest a possible causal link between global warming, brood caring behaviour and the decline of carrion crow population in the Mediterranean climatic region of Spain.

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.

Delayed egg-laying in Red-backed Shrike Lanius collurio in relation to increased rainfall in east-central Poland

Climate change has affected the breeding parameters of many animal species. In birds, most studies have focused on the effects of temperature on clutch phenology and clutch size. The long-term influence of other weather factors, including rainfall, on breeding parameters have been analysed much less often. Based on a 23-year dataset and 308 broods, we documented shifts in the timing of breeding, clutch size and mean egg volume in a long-distance migrant, the Red-backed Shrike Lanius collurio, from a central European population. We found a 5-day shift towards delayed breeding, but no differences in brood size or egg volume during those 23 years. The GLM analysis showed that the mean May temperature had a positive influence on the clutch initiation date, whereas the number of days with rain delayed laying. During the period 1999-2021, there was no change in the mean May temperature, but total precipitation and the number of days with rain in May increased. Thus, delayed nesting in this population was probably due to the increase in rainfall during this period. Our results provide a rare example of delayed nesting in birds in recent years. Predicted changes in the climate make it difficult to assess the long-term impact of global warming on the viability of Red-backed Shrike populations in east-central Poland.

Global warming modifies the seasonal distribution of clutches on a Mediterranean great tit population

Global warming has multiple effects on phenological events on a wide range of plants and animals. Specifically, many bird species have advanced the start of their breeding season, which could also imply an extension in its duration and also a change in the distribution of clutches throughout the breeding season. We have tested whether this occurred in a population of Great Tits (Parus major), in Sagunto (eastern Spain). The increase of March temperatures between 1986 and 2019 was related to an advancement of the breeding season. Although the breeding season was longer in years with higher June temperatures, the length did not show a temporal trend throughout the study period. The clutches were more concentrated at the beginning of the season (increase in the skewness), while the kurtosis ("tailedness" of the distribution) or the modality did not change significantly. Finally, the number of "equally good months" for breeding (a combined measure of length and distribution) has not changed throughout the years. Overall, all these phenological changes probably caused the observed increased proportion of pairs laying two clutches per year. It remains to be studied whether this increase in reproductive effort has positive or negative impact on fitness.

No Apparent Immediate Reproductive Costs of Overlapping Breeding and Moult in a Mediterranean Great Tit Population

Some phenological events in birds, such as breeding and moulting, are being affected by rising temperatures due to global warming, and many species have undergone temporary changes in these energetically demanding phases that are often separated in time. This has led to an increased overlap between breeding and moulting in some populations. This overlap causes conflicts in resource allocation and may impose fitness costs that could affect immediate reproductive performance. We tested whether this occurs in a great tit (Parus major) population in eastern Spain. In 71% of 390 pairs, in which both parents were captured during the period of overlap between moulting and breeding, at least one parent was moulting when feeding the chicks of its second brood. Later breeders were more likely to overlap breeding and moulting, and when both parents overlapped, clutch size was smaller, fewer eggs hatched and fewer fledglings in poorer body condition were produced. Some results were intermediate when only one parent moulted. However, all these differences between moulting and non-moulting pairs disappeared when the seasonal trend in reproductive parameters was taken into account, as moulting birds bred later and reproductive performance decreased seasonally. Therefore, the overlap of breeding and moulting does not impose additional reproductive costs in this population.

Complex associations of weather conditions with reproductive performance in urban population of a common waterbird

Weather conditions are recognized as one of key determinants of animal reproductive performance; however, the effect of weather on breeding success can be modulated by different features of breeding habitat. Constantly expanding urban areas cause significant changes in land cover and environmental conditions, but whether and how urban landscape mitigates weather impact on animal fitness remains little explored. The aim of this study was to investigate the association between weather parameters and reproductive performance in a reed-nesting waterbird species, the Eurasian coot Fulica atra. For this purpose, we performed a long-term monitoring of an urban coot population from central Poland, collecting data for over 400 breeding events. The results indicated that temperature may have contrasting effects on coot reproductive output at different stages of chick-rearing period (positive at early chick-rearing and negative at late chick-rearing). Also, contrary to our expectation, we found a positive relationship between mean daily precipitation in early chick-rearing period and reproductive output in our study population. Our study constitutes one of few examples showing how weather may affect fitness in urban wildlife and provides evidence for high complexity of associations between weather conditions and animal reproductive performance.

Fitness consequences of longer breeding seasons of a migratory passerine under changing climatic conditions

Numerous studies have shown that climate change affects the timing of migration and bird laying dates, but the resulting changes in the duration of breeding seasons and their fitness consequences remain largely unknown. We compared breeding parameters of 343 individually marked female Eurasian reed warblers, a multi-brooded migratory passerine, studied in the same area in 1980-1983 and 2005-2012. The latter period was warmer, with mean temperatures during the breeding season higher by 1.5°C on average. As, in recent years, birds arrive earlier from wintering areas and the breeding season of the population is longer, we hypothesized it should result in the increased re-nesting opportunities of individual females. We found that breeding periods of individual females (from building of the first nest till the end of caring for last fledglings/last nest failure) in the current century have extended by 2 weeks compared to the 1980s. In the 2000s, females produced 75% more fledglings annually than females in the 1980s (2.8 vs. 1.6, respectively). The proportion of females raising second broods increased from 2.7% to 23.6% between the first and the second study period while the share of females that did not produce any young annually decreased from 48.1% to 15.5%. The higher offspring production in recent years was related to more successfully fledged broods and an earlier start of breeding, which secured more time to re-nest. Higher female parental effort in recent years was not manifested in the reduction of the female apparent survival: it was almost identical in the two study periods (0.30 vs. 0.31). We conclude that prolonged reproductive seasons might be beneficial for some species. Identifying causes and consequences of changes in the duration of breeding seasons may be essential to predict demography of populations under changing climatic conditions.