Breeding Season Research Articles

Afro-Palaearctic migrant birds rid themselves of haemoparasite infections when breeding in the temperate zone.

In migratory passerines, the prevalence and parasitaemia of blood parasites often increase towards the end of the breeding season. Consequently, post-breeding migration to winter quarters can be seen as a strategy to avoid the rising pathogen pressure during this time (migratory escape). I studied haemoparasite infections in sedge warblers (Acrocephalus schoenobaenus) inhabiting natural wetlands in southern Poland, examining the same individuals just after their arrival from wintering grounds, and again during incubation or nestling feeding. The birds were found to be infected more often immediately after arrival than during subsequent sampling. Parasitaemia also decreased significantly as the season progressed. The health status of individuals appeared to improve during the breeding season, whereas the higher level of parasitaemia just after arrival suggests that infections had occurred earlier, on the wintering grounds or during migratory stopovers.

Clockwork precision: egg-laying-induced rise of body temperature is seasonally programmed in a wild bird

There is long time interest about the phenology of plants and animals living in seasonal environments as research in that field would help to understand the coping mechanisms leading to a higher fitness. For instance, it has been shown several decades ago that birds prepare themselves 2–4 months before the actual start of the breeding season by slowly growing reproductive organs. In parallel, the resting metabolic rate increase during reproduction in various vertebrates including mammals, reptiles, and birds. Recently, it has been reported that body temperature of a marine bird species was reaching an annual peak during egg-laying, raising the question about the seasonal dynamic of this important physiological feature. Using data loggers implanted in the abdominal cavity of female Common Eiders (Somateria mollissima mollissima) for a full year, we show here that daily body temperature (Tb.daily) is slowly increasing first and then accelerating at the approach of the laying period. Because the rise of Tb.daily is tightly associated with egg-laying in this species, we also analysed the influence of ambient temperature (water and air) and photoperiod on this seasonal dynamic. Based on the various mechanisms at work and a parsimonious interpretation of the data, we conclude that photoperiod is the main cue driving the seasonal breeding program of eiders. Although the laying dates of the instrumented females were highly clustered over a period of 4 years, we speculated that the remaining variation observed was the result of eco-physiological challenges occurring over the years.

Movements of adult and fledgling Carnaby’s Cockatoos (Zanda latirostris Carnaby, 1948) from eleven breeding areas throughout their range

Context Carnaby’s Cockatoo is an endangered species and the subject of a recovery plan. Aims Our study examined movements of adult and fledgling Carnaby’s Cockatoos from 11 breeding populations in southwestern Australia to establish where the cockatoos spent the non-breeding season (February–May) and sub-adult life-stage. Methods Data were collected on point-to-point movements from re-sightings and recoveries of cockatoos individually marked with patagial tags or leg bands. Sites were mostly located in the wheatbelt of Western Australia. Distribution patterns in the breeding and non-breeding seasons, including nesting sites were derived from location data from the Department of Biodiversity, Conservation and Attractions’ Threatened and Priority Database. Key results After breeding, adults and their fledglings moved from breeding areas to higher rainfall areas closer to the west and south coasts of south-western Australia where the food supply is greater and more reliable. Sub-adult cockatoos roam much more widely than adults and utilize foraging habitat not previously recognized as being important to this species. Conclusions Important foraging habitat and locations have been identified for breeding populations in the north and south of the range of Carnaby’s Cockatoos. Implications More conservation attention needs to be focussed on locating additional breeding populations, assessing the viability of these populations, and the extent and condition of their nesting and foraging habitat used during their non-breeding season. Conservation of Carnaby’s Cockatoo depends on the maintenance of remnant native vegetation and revegetation of nesting and foraging habitat throughout its range.

Nest secondary plants and their associations with haemosporidian blood parasites in blue tit females.

Avian nests often contain aromatic plant fragments, which has led to propose among others that they repel ectoparasites or vectors of blood parasites (‘nest protection hypothesis’). To date, the relationship between secondary plant provisioning and the parent's blood parasites remains unexplored. We investigated whether the presence of secondary plants in nests during different reproductive stages (before incubation, during incubation and nestling period) was associated with the presence of nest-dwelling ectoparasites and females’ blood-parasite infections in blue tits (Cyanistes caeruleus) during chick rearing. In this species, females are highly exposed to parasites, particularly at the beginning of the breeding season, since they build the nest and incubate alone. They also brood the nestlings while the male assists with provisioning. We found that females that provided fewer plants before incubation were more likely to be infected by Plasmodium. Specifically, Females that did not provide Achillea herbs before incubation were more likely to be infected by both Plasmodium and Haemoproteus, reinforcing the ‘nest protection’ hypothesis. Thus, secondary plants may create an early environment that masks the odour of hosts or repels vectors. Surprisingly, the presence of Lavandula during the nestling period was positively related to Leucocytozoon infection. Given its fastest development among haemosporidians, we speculate that Lavandula herbs are provided by females to reduce mother-to-offspring transmission or as a self-medication strategy. Finally, the number of plant fragments provided before incubation was negatively associated with the number of (Protocalliphora azurea) larvae, whereas there were no associations with the presence of mites (Dermanyssus gallinoides).

Using unmanned aerial vehicles to estimate body volume at scale for ecological monitoring

Abstract Demographic data are essential to construct mechanistic models to understand how populations change over time and in response to global threats like climate change. Existing demographic data are either lacking or insufficient for many species, particularly those that are challenging to obtain direct measurements from that can be used to estimate demographic rates, like marine mammals. A method for collecting accurate demographic data to construct robust demographic models at scale would fill this knowledge gap for difficult‐to‐access species. We introduce a novel, non‐invasive method to estimate the 3D body size (volume) of pinnipeds (seals, sea lions and walruses) that will allow monitoring at high spatial and temporal scales. Our method integrates 3D structure‐from‐motion photogrammetry data collected via planned flight missions using off‐the‐shelf, multirotor unmanned aerial vehicles (UAVs). We apply and validate this method on the grey seal Halichoerus grypus, a pinniped species that spends much of its time at sea but is predictably observable during its annual breeding season. We investigate the optimal ground sampling distance (GSD) for surveys by calculating the success rates and accuracy of volume estimates of individuals at different altitudes. Based on current technology, we establish an optimal GSD of at least 0.8 cm px−1 for animals similar in size to UK grey seals (~1.2–2.5 m length), making our method reproducible and applicable to other species. We found volume estimates were accurate and could be successfully estimated for up to 68% of hauled‐out seals in study areas. Our method accurately estimates individual body volume of pinnipeds in a time‐ and cost‐effective manner while minimising disturbance. While the approach is applied to pinnipeds here, the method could be adapted to further taxa that are otherwise challenging to obtain direct measurements from. Our proposed approach therefore has the potential to fill demographic research gaps, which will improve our ability to protect and conserve species into the future.

Contribution of disease to Australian sea lion (Neophoca cinerea) pup mortality at Seal Bay, Kangaroo Island, 2016–2022

AbstractThe endangered Australian sea lion (Neophoca cinerea) population is declining, and its conservation is threatened by the species' low fecundity and high pup mortality. This study details reasons for pup deaths and quantifies the impacts of disease and comorbidity. Of 284 dead pups reported from five breeding seasons (2016–2022) at the Seal Bay colony, Kangaroo Island, gross necropsy was conducted on 122, with fecal analysis for hookworm (Uncinaria sanguinis) detection, tissue histology, and bacterial culture performed on subsets. Determinable primary causes of mortality were conspecific trauma (± comorbidity, 41.0%), starvation (24.6%), and infectious disease (hookworm‐associated hemorrhagic enteritis [HAHE] ± bacterial infection, 19.7%). Allowing for comorbidity, 37.7% of pups died with an infectious disease, including 44.0% of deaths with trauma and 41.5% with starvation. In higher mortality summer‐autumn breeding seasons, pups were at greater risk of trauma (p = .001) and subsequent bacterial infection (p < .001). Parasiticide treatment significantly reduced HAHE‐associated (p = .005) and overall mortality (p < .001) risk, suggesting hookworm infection increases pup susceptibility to other causes of mortality. Although the exact causal pathways for this treatment‐related overall mortality benefit remain to be confirmed, intervention appears highly impactful and could benefit species conservation efforts.

Rainfall is associated with divorce in the socially monogamous Seychelles warbler.

Divorce-terminating a pair bond whilst both members are alive-is a mating strategy observed in many socially monogamous species often linked to poor reproductive success. As environmental factors directly affect individual condition and reproductive performance, they can indirectly influence divorce. Given current climate change, understanding how environmental fluctuations affect partnership stability has important implications, including for conservation. Yet, the relationship between the environment and divorce remains largely unstudied. We examined the influence of temporal environmental variability on the prevalence of within- and between-season divorce and the possible underlying mechanisms in a socially monogamous passerine. Analysing 16 years of data from a longitudinal dataset, we investigated the relationship between rainfall and divorce in the Seychelles warbler (Acrocephalus sechellensis). First, we performed climate window analyses to identify the temporal windows of rainfall that best predict reproductive success and divorce. Then, we tested the effects of these temporal windows of rainfall on reproductive success and divorce and the influence of reproductive success on divorce whilst controlling for covariates. Annual divorce rates varied from 1% to 16%. The probability of divorce was significantly associated with the quadratic effect of 7 months of total rainfall before and during the breeding season, with divorce increasing in years with low and high rainfall. This quadratic relationship was driven by a heavy rainfall event in 1997, as excluding 1997 from our analyses left a significant negative linear relationship between rainfall and divorce. Although the same temporal window of rainfall predicting divorce significantly influenced reproductive success, we found no significant correlation between reproductive success and divorce. Our findings suggest that rainfall impacts divorce. Given that this effect is likely not directly mediated by reproductive success, we discuss other possible drivers. Although the 1997 super El Niño event shows how heavy rainfall may affect socially monogamous partnerships, more data are required to estimate the robustness of this effect. By adding to the growing body of literature showing that environmental conditions influence the stability of socially monogamous partnerships, we provide novel insights that may also be important for conservation efforts in times of climate change.

Drivers of Interspecific Spatial Segregation in Two Closely‐Related Seabird Species at a Pan‐Atlantic Scale

ABSTRACTAimEcologically similar species living in sympatry are expected to segregate to reduce the effects of competition where resources are limiting. Segregation from heterospecifics commonly occurs in space, but it is often unknown whether such segregation has underlying environmental causes. Indeed, species could segregate because of different fundamental environmental requirements (i.e., ‘niche divergence’), because competitive exclusion at sympatric sites can force species to either change the habitat use they would have at allopatric sites (i.e., ‘niche displacement’) or to avoid certain areas, independently of habitat (i.e., ‘spatial avoidance’). Testing these hypotheses requires the comparison between sympatric and allopatric sites. Understanding the competitive mechanisms that underlie patterns of spatial segregation could improve predictions of species responses to environmental change, as competition might exacerbate the effects of environmental change.LocationNorth Atlantic and Arctic.TaxaCommon guillemots Uria aalge and Brünnich's guillemots Uria lomvia.MethodsHere, we examine support for these explanations for spatial segregation in two closely‐related seabird species, common guillemots (Uria aalge) and Brünnich's guillemots (U. lomvia). For this, we collated a pan‐Atlantic data set of breeding season foraging tracks from 1046 individuals, collected from 20 colonies (8 sympatric and 12 allopatric). These were analysed with habitat models in a spatially transferable framework to compare habitat preferences between species at sympatric and allopatric sites.ResultsWe found no effect of the distribution of heterospecifics on local habitat preferences of the focal species. We found differences in habitat preferences between species, but these were not sufficient to explain the observed levels of spatial segregation at sympatric sites.Main ConclusionsAssuming we did not omit any relevant environmental variables, these results suggest a mix of niche divergence and spatial avoidance produces the observed patterns of spatial segregation.

Environmental DNA reveals a presence of Anser fabalis (Bean Goose) and an absence of A. erythropus (Lesser White-fronted Goose) in Finnish Northern Lapland

Abstract Detecting rare and elusive species from vast wilderness areas poses significant challenges. The Fennoscandian population of Anser erythropus (Lesser White-fronted Goose) is among the most endangered bird populations in Europe, with only 25–30 breeding pairs remaining in Northern Norway. Historically, its former breeding range extended across the mountainous regions of Fennoscandia. Thanks to targeted conservation efforts during the 21st century, A. erythropus has started to recolonize some of its former breeding areas in Norway and possibly also in Finland. Anser serrirostris rossicus (Tundra Bean Goose) is classified as Endangered (EN) in Finland, with just a few breeding pairs in northernmost Finnish Lapland with a poorly known breeding range. It breeds in higher numbers in Finnmark Norway and is listed as Vulnerable (VU) in Norway. Anser fabalis fabalis (Taiga Bean Goose), classified as Endangered in Norway, can also breed in the same area in low numbers. To locate individuals of these elusive goose species during breeding seasons, we used environmental DNA (eDNA) extracted from filtered lake water from selected lakes in northern Finland. We amplified and sequenced a short region of the mitochondrial control region to identify the species. Additionally, for positive controls, we sampled eDNA from the water of a Finnish spring staging site and known Norwegian breeding sites of the A. erythropus, from which eDNA of the A. erythropus was identified. eDNA of the A. erythropus was not detected within the former Finnish breeding range. Based on this, the A. erythropus has either not recolonized its former breeding habitats in Finland, the correct lakes were not sampled, the eDNA concentration was below detection limits, or due to other methodological issues. Anser serrirostris rossicus was detected in 3 lakes and A. fabalis fabalis in 10 lakes, providing new information about the breeding distribution of Bean Geese in Finnish Lapland.

Artificial Light at Night Advances the Onset of Vocal Activity in Both Male and Female Great Tits During the Breeding Season, While Noise Pollution Has Less Impact and Only in Females

Artificial light at night (ALAN) and noise pollution are two important stressors associated with urbanisation that can have a profound impact on animal behaviour and physiology, potentially disrupting biological rhythms. Although the influence of ALAN and noise pollution on daily activity patterns of songbirds has been clearly demonstrated, studies often focus on males, and the few that examined females have not included the potential influence of males on female activity patterns. Using free-living pairs of great tits (Parus major) as a model, we examined for the first time the effects of ALAN and noise pollution and their interaction on the onset of (vocal) activity in both members of a pair. We focused on the egg-laying phase, when both sexes are most vocally active. The onset of male dawn song, female emergence time from the nest box and the onset of female calling in the nest box were measured and used as a proxy for the chronotype. The repeatabilities for all chronotype proxies were high, with higher repeatabilities for males. Consistent with previous studies, ALAN advanced the onset of male dawn song, while it did not elicit a strong response in female emergence time. Additionally, our results suggest an indirect effect of ALAN on the onset of female vocal activity via acoustic interaction with the male. Noise pollution advanced the emergence time in females, while an interaction between ALAN and noise pollution was found for the onset of female calling. In agreement with previous studies, several covariables were shown to have an influence on the activity onset. Taking several proxies for chronotype into account, this study has provided robust evidence of effects of ALAN on male and female cavity-nesting songbirds during the egg-laying period.

Fluctuating population density of the goby Lubricogobius exiguus during the breeding season with artificial nests at Oto Beach, Kagoshima, southern Japan

AbstractCryptobenthic reef fish (CRF), which are benthic reef fish with body lengths of less than 50 mm, generally exhibit life history characteristics, such as a short lifespan, early maturation, high mortality, and microhabitat specialization. In this study, we investigated breeding season and population fluctuation patterns of a gobiid CRF fish Lubricogobius exiguus. At our field study site, the breeding season of L. exiguus extended from April to November. The population densities of L. exiguus fluctuated considerably, starting at low density early in the breeding season, increasing to a peak in the middle of the season, and stabilizing at a medium density by the end of the season. This seasonal pattern was influenced by two peaks in juvenile recruitment, and the adult population increased after these peaks. The fluctuating numbers of juveniles and adults suggest that some individuals may have a short post-settlement lifespan of less than 80 days.

The Influence of Building Surroundings and Glass Cover in Bird Collisions

The characteristics of building surroundings can influence the number of bird deaths caused by collisions with glass structures. Thus, this study investigated whether the number of trees, the distance to the nearest tree, the number of fruit trees, and the glass area influenced the number of bird collisions on a university campus in Brazil from March 2017 (breeding and non-breeding seasons) to January 2018 (breeding season). Twenty-four birds died due to collisions with the windows in the one-year sampling. Among the factors evaluated, the number of trees and the area of the glass predicted the number of deaths from collisions. The greater the number of trees and the glass area, the greater the number of bird collisions. This suggests that the more vegetation there is near windows, the more birds are attracted, and the less visible the glass barrier becomes, possibly due to the appearance of trees in reflections or scenes viewed through the glass, making it difficult for birds to distinguish the real landscape from the reflected environment. If large expanses of glass are placed on buildings near vegetation, including trees, more bird collisions will occur. Thus, to reduce bird collisions, building designs should reduce the amount of glass used on building exteriors near vegetation and ensure the glass is treated with visual markers.

Climate and ecology predict latitudinal trends in sexual selection inferred from avian mating systems.

Sexual selection, one of the central pillars of evolutionary theory, has powerful effects on organismal morphology, behaviour, and population dynamics. However, current knowledge about geographical variation in this evolutionary mechanism and its underlying drivers remains highly incomplete, in part because standardised data on the strength of sexual selection is sparse even for well-studied organisms. Here, we use information on mating systems-including the incidence of polygamy and extra-pair paternity-to estimate the intensity of sexual selection in 10,671 (>99.9%) bird species distributed worldwide. We show that avian sexual selection varies latitudinally, peaking at higher latitudes, although the gradient is reversed in the world's most sexually selected birds-specialist frugivores-which are strongly associated with tropical forests. Phylogenetic models further reveal that the strength of sexual selection is explained by temperature seasonality coupled with a suite of climate-associated factors, including migration, diet, and territoriality. Overall, these analyses suggest that climatic conditions leading to short, intense breeding seasons, or highly abundant and patchy food resources, increase the potential for polygamy in birds, driving latitudinal gradients in sexual selection. Our findings help to resolve longstanding debates about spatial variation in evolutionary mechanisms linked to reproductive biology and also provide a comprehensive species-level data set for further studies of selection and phenotypic evolution in the context of global climatic change.

Sick without signs. Subclinical infections reduce local movements, alter habitat selection, and cause demographic shifts

In wildlife populations, parasites often go unnoticed, as infected animals appear asymptomatic. However, these infections can subtly alter behaviour. Field evidence of how these subclinical infections induce changes in movement behaviour is scarce in free-ranging animals, yet it may be crucial for zoonotic disease surveillance. We used an ultra-high-resolution tracking system (ATLAS) to monitor the movements of 60 free-ranging swallows every 8 seconds across four breeding seasons, resulting in over 1 million localizations. About 40% of these swallows were naturally infected with haemosporidian parasites. Here, we show that infected individuals had reduced foraging ranges, foraged in lower quality habitats, and faced a lowered survival probability, with an average reduction of 7.4%, albeit with some variation between species and years. This study highlights the impact of subclinical infections on movement behaviour and survival, emphasizing the importance of considering infection status in movement ecology. Our findings provide insights into individual variations in behaviour and previously unobservable local parasite transmission dynamics.

Seabird and sea duck mortalities were lower during the second breeding season in eastern Canada following the introduction of highly pathogenic avian influenza A H5Nx viruses

ABSTRACT Capsule H5N1 clade 2.3.4.4b viruses have caused significant mortality events in various wild bird species across Europe, North America, South America, and Africa. In North America, the largest impacts on wild birds have been in eastern Canada, where at least 40,391 wild birds were reported to have died from highly pathogenic avian influenza (HPAI) between April and September 2022. Aims To apply previously established methods to collect and quantify the total reported wild bird mortality in eastern Canada from October 2022 to September 2023. Methods We documented the spatial, temporal, and taxonomic patterns of wild bird mortality in the 12 months that followed a mass mortality event in the summer of 2022, and then quantified the observed differences in mortality across the spring and summer (April to September) of 2022 and 2023. In eastern Canada, there was high uncertainty about whether 2023 would bring another year of devastating HPAI-linked mortalities. Results Mortalities in the spring and summer of 2023 were 93% lower than in 2022, but encompassed a wider diversity of species. Mortalities in the fall/autumn and winter (non-breeding season) were dominated by waterfowl, while mortalities during the spring and summer (breeding season) were dominated by seabirds. Due to a low prevalence of HPAI among a subset of tested birds, we cannot broadly attribute the reported mortalities in 2023 to HPAI. However, our analysis did identify three notable mortality events linked to HPAI, involving at least 1646 Greater Snow Geese Anser caerulescens atlanticus, 232 Canada Geese Branta canadensis, and 212 Northern Gannets Morus bassanus. The latter reflected the continuation of a mortality event from the Northern Gannet’s 2022 breeding season. Conclusions This study emphasizes the ongoing need for H5Nx surveillance and mortality assessments as the patterns of mortality in wild populations continue to change.

A case study of the 2023 highly pathogenic avian influenza (HPAI) outbreak in tern (Sternidae) colonies on the east coast of the Republic of Ireland

ABSTRACT Capsule:HPAI H5N1 had a significant impact on breeding Common Terns Sterna hirundo, Arctic Terns Sterna paradisaea and Roseate Terns Sterna dougallii on the east coast of the Republic of Ireland (ROI) in 2023, with a lesser impact on Sandwich Terns Thalasseus sandvicensis and only two cases among Little Terns Sternula albifrons. Aims: To document the outbreak of HPAI H5N1 in the tern colonies on the east coast of ROI during the 2023 breeding season. Methods:Precautions were taken from the start of the breeding season, including personal protective equipment (PPE) and safe operating procedures. Regular meetings were held between BirdWatch Ireland and the National Parks and Wildlife Service (NPWS) to respond to the emerging situation. Once HPAI was confirmed in a colony, all ringing and nest visits were stopped. Carcass removal was carried out at all affected colonies and most carcasses were incinerated. Results: Common Terns suffered the highest mortality across all colonies in 2023, with smaller but notable numbers of dead Roseate Terns and Arctic Terns, but very few Sandwich Terns and only two Little Tern deaths were attributed to HPAI. Conclusion: Regular meetings between relevant organizations were invaluable in preparing for outbreaks and ensuring an adaptive approach as the situation changed over time and between colonies. There was no way of knowing if the actions taken were effective, as the pattern of virus spread between species and sites remains poorly understood. Future clarity over the role of various state agencies and other relevant bodies in responding to HPAI in wild birds, greater sharing of real-time information, and pre-arranged agreements to ensure rapid testing and disposal of carcasses, would be useful to ensure an effective response to future outbreaks.

Reaction of two sciaenid species to passing boats: Insights from passive acoustic localisation

Meagre (Argyrosomus regius) and weakfish (Cynoscion regalis) are two soniferous sciaenid species that use the Tagus estuary (Portugal) to breed. In this highly urbanized environment, fishes must deal with multiple anthropogenic stressors that include high noise levels caused by the intense boat traffic. We investigated how these sciaenids react to ferry boat and small boat passages, by assessing both changes in breeding calling activity with passive acoustic monitoring and escape responses with passive acoustic localisation. We found that meagre reduced calling activity after boat passages, but no such effect was observed in weakfish. Instead, weakfish moved in response to boat passages suggesting an escape response. Meagre also changed positions and dispersion patterns, but movements were more modest. This study uses a cost-effective and non-invasive passive acoustic localisation method to elucidate the behavioural response of soniferous fish to anthropogenic noise for the first time, contributing to our understanding of the way fish react to this stressor. Such knowledge is especially important in contexts where fish are exposed to highly prevalent human-generated noise during the breeding season, such as in busy estuaries and coastal areas.

The interplay of resource availability and parent foraging strategies on juvenile sparrow individual specialization

Temporal variation in resource availability, amplified by global change, may have strong impacts on species breeding at temperate and high latitudes that cue their reproduction to exploit seasonal resource pulses. This study examines how resource availability and parental care influence niche partitioning between and within age classes in the rufous‐collared sparrow, which provides extensive parental care. We hypothesized juveniles would exhibit narrower niches focused on high‐quality resources compared to adults, regardless of resource availability. We used stable isotope analysis to quantify individual and population niches in juveniles and adults across the breeding season in two cohorts experiencing contrasting resource landscapes. Contrary to our initial hypothesis, juveniles exhibited greater among‐individual diet variation and smaller total niche widths (i.e. higher levels of individual specialization, IS) during periods of high food availability in comparison to periods of food scarcity. Interestingly, total niche width and IS of adults remained stable across seasons despite a shift in trophic level, highlighting their potential role in providing a consistent diet for their young. These findings reveal a dynamic interplay between resource availability, parental care, and IS, with important implications for understanding population resilience under variable resource scenarios. The study also suggests that adult sparrows modify their provisioning strategies based on resources, potentially buffering offspring from environmental fluctuations. Understanding age‐specific responses to resource variation is crucial for predicting species responses to ecological conditions, particularly in regions like central Chile where seasonal resource limitation is expected to become more variable in response to climate change.

Changes of nestling ringing dates in nine bird species over seven decades

Climate change co-occurs with an advancement of avian breeding season (indexed as laying dates or fledging dates) in the temperate zone, suggesting a causality between them. Here, we investigate whether the long-term shifts in nestling (chick) ringing dates also mirror this phenomenon. This index is biased by inherent shortcomings, such as the non-independence of dates (in nestmates, colony members), poor accuracy (long period suitable for ringing), and strange shape of distributions. These shortcomings can be reduced by applying the median of annual ringing dates as an index of breeding phenology. The advantage of this index is that data are available for long periods and large sample sizes. By accepting certain compromise between statistical discipline and fieldwork realities, we examined changes in the breeding phenology of 9 bird species from 1951 to 2020 in Hungary. We found that the annual median of ringing dates advanced significantly (by 9–14 days) in the Black-headed Gull, Common Kestrel, Barn Swallow, Great Tit, and Eurasian Blue Tit. Contrarily, no significant (all P > 0.16) changes occurred in the case of the Common Tern, Black-crowned Night-heron, Common Buzzard, and Long-eared Owl. We also found that the proportion of Great Tits’ second brood has been reduced in recent decades.

Precipitation and female experience are major determinants of the breeding performance of Canarian houbara bustards

Precipitation is one of the main triggers of reproduction in desert‐breeding birds. The unpredictability of rainfall patterns in arid environments has led species to adapt their breeding effort to episodes of abundant food after rainfall. The response is not the same for all individuals in a population, and may vary especially with the age and experience of each female. Here we investigate the effects of precipitation, temperature, body size and breeding experience, among other variables, on reproductive parameters of 20 females of Canarian houbara bustard (Chlamydotis undulata fuertaventurae), an endangered desert bird endemic of the eastern Canary Islands. Precipitation and breeding experience were the main determinants of female breeding performance. Higher rainfall determined an increase in nesting rate, and earlier autumn rains caused an advancement of nesting to October, allowing the breeding season to be extended to eight months. This favoured an extraordinary increase in productivity in more rainy breeding seasons, with 15 times more females nesting in the two most rainy winters than in dry years. In addition, females with more breeding experience showed a higher tendency to breed, higher nest attempt and fledging success, and longer breeding season, which allowed them to rear more chicks. A female even double brooded successfully in the same season, which, considering that chicks remain with the mother for up to six months, indicates a great capacity to optimise reproductive investment, by adapting to highly variable rainfall regimes. In recent decades, the eastern Canary Islands have undergone a process of aridification, and climate models predict a medium‐term increase in the frequency and duration of drought periods. Thus, Canarian houbaras are particularly vulnerable to climate change, so measures are urgently needed to reduce their mortality and improve the quality of their habitat, in order to favour their reproduction and prevent their extinction.