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

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.

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.

Analysis of Prey Composition in Eurasian Reed Warblers’ Acrocephalus scirpaceus Droppings at Four Breeding Sites in Italy

Our aim was to investigate the among-populations diversity of prey composition in Eurasian Reed Warblers’ diets via their droppings, both to assess the ecological validity of this sampling method and to test whether the prey species most abundant in fecal samples were also the most present in the Italian study site. We collected fecal samples at four sites throughout Italy, for a total of 144 samples. Within reedbeds, the breeding habitat of the Eurasian Reed Warbler, we also collected arthropods by carrying out entomological sweepings at one of the study sites. Within the fecal samples, we identified dozens of prey species, belonging mainly to Araneae, Coleoptera, Diptera, Hymenoptera and Aphidoidea taxa, whose compositions were not statistically different among sites. The commonest prey species were Coleoptera in the droppings (68.5%) and Diptera in the reedbeds (31.3%), although the latter was less numerous in the fecal samples. The diets of different Italian populations of Eurasian Reed Warbler emerging from our study underline a strong Coleopteran presence, without differences across Italy. Fecal samples appear to be an exhaustive method to study variation in Eurasian Reed Warbler diet and its ecological importance; however, although potential caveats do exist, such as the possible under-representation of Diptera.

Anthropogenic habitat modification alters calling phenology of frogs

Anthropogenic habitat modification significantly challenges biodiversity. With its intensification, understanding species' capacity to adapt is critical for conservation planning. However, little is known about whether and how different species are responding, particularly among frogs. We used a continental-scale citizen science dataset of >226,000 audio recordings of 42 Australian frog species to investigate how calling-a proxy for breeding-phenology varied along an anthropogenic modification gradient. Calling started earlier and breeding seasons lengthened with increasing modification intensity. Breeding seasons averaged 22.9 ± 8.25 days (standard error) longer in the most modified compared to the least modified regions, suggesting that frog breeding activity was sensitive to habitat modification. We also examined whether calls varied along a modification gradient by analysing the temporal and spectral properties of advertisement calls from a subset of 441 audio recordings of three broadly distributed frog species. There was no appreciable effect of anthropogenic habitat modification on any of the measured call variables, although there was high variability. With continued habitat modification, species may shift towards earlier and longer breeding seasons, with largely unknown ecological consequences in terms of proximate and ultimate fitness.

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.

Population specific annual cycles and migration strategies in a leap-frog migrant

Abstract

A common migratory pattern in birds is that northerly breeding populations migrate to more southerly non-breeding sites compared to southerly breeding populations (leap-frog migration). Not only do populations experience differences in migration distances, but also different environmental conditions, which may vary spatiotemporally within their annual cycles, creating distinctive selective pressures and migratory strategies. Information about such adaptations is important to understand migratory drivers and evolution of migration patterns. We use light-level geolocators and citizen science data on regional spring arrivals to compare two populations of common ringed plover Charadrius hiaticula breeding at different latitudes. We (1) describe and characterize the annual cycles and (2) test predictions regarding speed and timing of migration. The northern breeding population (NBP) wintered in Africa and the southern (SBP) mainly in Europe. The annual cycles were shifted temporally so that the NBP was always later in all stages. The SBP spent more than twice as long time in the breeding area, but there was no difference in winter. The NBP spent more time on migration in general. Spring migration speed was lower in the SBP compared to autumn speed of both populations, and there was no difference in autumn and spring speed in the NBP. We also found a larger variation in spring arrival times across years in the SBP. This suggests that a complex interaction of population specific timing and variation of breeding onset, length of breeding season, and proximity to the breeding area shape the annual cycle and migratory strategies.

Significance statement

Migration distance, climate, and the resulting composition of the annual cycle are expected to influence migration strategies and timing in birds. Testing theories regarding migration behaviours are challenging, and intraspecific comparisons over the full annual cycle are still rare. Here we compare the spatiotemporal distributions of two latitudinally separated populations of common ringed plovers using light-level geolocators. We found that there was a larger long-term variation in first arrival dates and that migration speed was slower only in spring in a temperate, short-distance migratory population, compared to an Arctic, long-distance migratory population. This suggests that a complex interaction of population specific timing and variation of breeding onset, length of breeding season and proximity to the breeding area shape the annual cycle and migratory behaviours.

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.