Tamás Székely

Nesting site selection has key fitness consequences for both parents and their offspring. Despite previous investigations of the factors influencing the nesting decisions of varied taxa, the relative roles of the sexes in nesting decisions in species with biparental care remain unclear. We investigated nest cover selection in a biparental shorebird (Kentish Plover Anarhynchus alexandrinus ) characterised by variation in nesting strategies, including nests laid under vegetation (covered nests) and unconcealed nests laid in the open (open nests). We firstly described seasonality in natural variation in nest cover selection. Secondly, we investigated whether males or females are consistent in their nest cover choice after an experimental removal of their partner and clutch. We show that Kentish Plover predominantly choose open versus covered nests, but that this pattern is accentuated later in the season due to a seasonal decline in covered nests. Our experiment revealed no difference in the tendency to select covered versus open nests after partner removal in either sex, indicating no directional change in nest cover choice following a simulated predation event. Moreover, male and female consistency in nest cover choice decisions over successive nesting attempts was low and did not differ between the sexes. Our findings indicate that the nest cover choice of individual males and females following a predation event are highly dynamic and that neither sex enforces consistent nest cover preferences. Our work suggests renesting decisions may be highly context dependent and emphasises the need for further experimental studies to understand the mechanisms and trade-offs underlying parental decisions.

Nest site selection is a key reproductive decision in ground‐nesting birds, given its direct consequences for breeding success and survival of the parent(s). Studies in extreme hot environments show that cover (e.g., vegetation, rocks) that provides shade at the nest can strongly shape parental incubation behaviour. Understanding the generality of these effects across differing environments, including less extreme climates, is an important goal in predicting the behavioural and reproductive impacts of rising global temperatures. Here we investigated how nest cover influences biparental incubation effort and sex‐specific investment in a wild population of Kentish Plovers breeding in a Mediterranean environment. We used 24‐h video recordings from 24 nests with variable nest cover that ranged from fully open (0% coverage) to complete coverage (100%). Contrary to previous work that indicates less covered nests require more parental effort to shield embryos from thermal extremes, we found that nest cover was not associated with total incubation, mean off‐nest duration, or male incubation share. However, we detected a non‐significant trend for a higher frequency of off‐nest periods in more covered nests. Our results suggest that nest cover is not a strong modulator of incubation behaviour in our population, suggesting that in some circumstances nest cover may primarily impact aspects of incubation other than thermoregulation, such as protection from visual predators, wind exposure or precipitation. Despite no observed difference in incubation patterns, we cannot preclude the possibility that parents nesting in low cover sites are exposed to greater heat stress, but such heat stress and physiological costs are not reflected in changes in incubation. We propose comparative studies of biparental ground‐nesting species across climatic gradients to identify the adaptations associated with breeding in hot climates that include behaviour, heat tolerance and nest cover.

Incubation is a critical phase of reproduction, during which parents must balance the thermal requirements of embryos with time spent away from the nest for self-maintenance. In species with unipar...

The adult sex ratio (ASR; the proportion of males in the adult population) is a key demographic trait that varies widely across species and is linked to mating systems and sexually selected traits. Previous research on wild tetrapods showed that ASR is associated with genotypic sex determination system: species with male-heterogamety (XY sex chromosome system) tend to have more female-biased ASRs than species with female-heterogamety (ZW system). If genotypic mechanisms of sex determination are involved, these may also shape ASRs in controlled environments. Here, we test the latter proposition using demographic data from 1,192 zoo-housed reptile, bird, and mammal species. Across amniotes, ASRs in captive populations follow patterns similar to those observed in the wild: XY species tend to have more female-biased ASRs than ZW species. Captive mammals and birds showed similar ASR biases as found in wild populations, although in reptiles, the clade with diverse sex determination systems, the ASR did not differ significantly between XY and ZW species. Instead, reptiles with temperature-dependent sex determination (TSD) differed from reptiles of both genotypic sex determination groups. Together these results support that non-ecological processes linked to sex determination systems contribute to ASR patterns both in captive and wild animals.

Tyrannosaurs were giant predatory dinosaurs that occupied the apex of Late Cretaceous food chains. Little is known about the early life and reproductive ecology of tyrannosaurs due to the extreme rarity of hatchling and juvenile fossils. We report bones of hatchlings (Tyrannosaurus rex and Gorgosaurus libratus, weighing ~2.5 kg and ~2.4 kg, respectively, i.e., T. rex versus ~30 eggs in the largest T. rex, and clutches of ~15 eggs in G. libratus; larger clutches of 50 or even 100 eggs are not impossible. This suggests an r-selected reproductive strategy. Synchrotron scans reveal Haversian bone remodeling, suggesting that tyrannosaurs moved soon after hatching. Hatchling tyrannosaurs’ small size and precociality suggest limited parental care; teeth of hatchlings show wear suggesting that they fed on relatively large vertebrates. Tyrannosaurs had proportionately larger offspring than most reptiles, but relatively smaller hatchlings than Eumaniraptora and birds, suggesting retention of a primitive reproductive strategy intermediate between that of basal diapsids and birds. Multiple dinosaur lineages evolved large eggs independently, suggesting an evolutionary trend towards increased parental investment.

Sexual size dimorphism (SSD) arises from sex‐specific selection on body size, primarily through sexual selection, mortality‐driven selection on males, and fecundity selection on females. A key ecological factor that may shape both processes is foraging behaviour, which determines movement, predation exposure and resource acquisition. Spiders provide a useful model system to test this idea because they exhibit extensive ecological diversity in prey‐capture strategies, and previous work has linked hunting strategies to reproductive traits, body size and SSD. However, these relationships remain poorly resolved and rarely tested within a comparative mechanistic framework. Here, using a phylogenetic comparative analysis of 264 species across eight hunting guilds, we tested whether hunting guild predicts variation in SSD and modulates the relationship between SSD, sex‐biased mortality and fecundity. We used sex differences in pitfall trap catches, taken from the literature, as a proxy for sex differences in mobility and mortality. SSD differed markedly among guilds, with the strongest female bias occurring in orb‐web weavers. The relationship between SSD and sex‐biased mobility/mortality was context‐dependent, emerging in sheet weavers but not in ground hunters. In contrast, we consistently predicted female and male body size, but not SSD, with effect sizes varying across guilds. Together, these results suggest that SSD does not arise from universal mechanisms, but from guild‐specific sexual asymmetries associated with mobility, predation exposure, and resource access, linking foraging strategy to the macroevolution of body size differences between the sexes.

The African jacana (Actophilornis africanus, family Jacanidae) is a sex-role-reversed waterbird inhabiting tropical and subtropical open wetlands across Africa. Identifying environmental factors that influence nest site distribution and suitable nesting habitats is crucial for protecting species and habitat management; however, studies addressing these factors remain limited for this species. This study aimed to map suitable nesting habitats and identify the main environmental variables influencing the nest site distribution of the African jacana in Lake Hawassa, Ethiopia. We mapped nesting habitat suitability using a Maximum Entropy (MaxEnt) model and ArcGIS Pro 3.2.2 based on 78 field-collected nest data points and ten environmental variables. The model predicted a total suitable nesting habitat area of 1.25 km² with high accuracy (AUC = 0.90, CBI = 0.8, and omission rate = 0.22), representing about 1.2% of Lake Hawassa’s total area. In general, suitable nesting habitats were relatively small, fragmented, and mainly clustered along the southeastern shore of Lake Hawassa. The mean precipitation and temperature during the breeding season, slope, elevation, and distance to shoreline were the main predictors of the African jacana’s nesting habitat suitability. The results of the present study provide valuable insights into local wetland management and the conservation of African jacanas and other breeding waterbirds in Lake Hawassa. Moreover, this study establishes baseline information for assessing how future climate and habitat changes may influence breeding habitat suitability in similar Ethiopian wetlands. The present study was limited to nesting habitat suitability based on limited environmental factors and did not include nest success, pollution parameters or predation; future studies incorporating these factors may improve ecological interpretation.

The adult sex ratio plays a crucial role in shaping breeding systems and traits linked to sexual selection. Recent studies associate adult sex ratio with mate choice, pair-bonding, and parenting, as the rarer sex gains advantages in mate selection and parental investment. However, the causal relationships between the demographic factors that generate adult sex ratio bias and its broader implications remain debated. Skewed adult sex ratios can result from sex-biased mortality and maturation, which influence mating and parental behaviours. Conversely, the costs of these behaviours may further drive sex differences in mortality and maturation, reinforcing adult sex ratio biases. Here, we compile demographic and behavioural data from 261 bird species across 69 families to examine these associations within a phylogenetic framework. Our analyses confirm that demographic traits are associated with adult sex ratio and reveal links between adult sex ratio, pre-copulatory sexual selection, and parenting. Phylogenetic path analyses further demonstrate that sex differences in mortality and maturation drive adult sex ratio biases, which subsequently influence mating and parenting rather than the reverse. This study provides a comprehensive analysis of the interplay between demography, social environment, and breeding systems, highlighting adult sex ratio as a crucial link. Our findings underscore the need for further research on the demographic underpinnings of social behaviour and reproductive strategies.

Annual survival is a key demographic parameter driving population trends in wildlife populations. However, despite numerous species‐specific or regional studies, global reviews of the factors affecting the survival of declining taxa remain scarce. Here, we investigated annual survival of fledged immature and adult shorebirds, a globally‐distributed and substantially‐declining avian taxon exhibiting diverse life‐history and migration strategies. We compiled 796 estimates of annual survival from 436 populations of 105 species, spanning 133 years from 1891–2023. Next, we investigated temporal and spatial trends and the impact of different life‐history traits on survival in a phylogenetic and spatial framework on a robust subset of 418 estimates from 1980 to the present. As expected, annual survival of adults was higher than immatures, and increased with body mass. Survival declined with longer migration distance, and marginally with breeding latitude. Additionally, annual survival significantly declined since 1980, especially among adult shorebirds. In contrast to previous analyses, neither insularity nor flyway type affected annual survival, and with small differences among continents. We concluded that annual survival did not show clear spatial patterns, but has declined substantially over recent decades. Some characteristics, including migratory behaviour, might make some populations of shorebirds more vulnerable than others. However, poor data coverage in some regions and methodological limitations might still mask local temporal and spatial patterns in the survival rates. The continuing collection of standardised data for population‐specific demographic parameters of wild animals is essential for a better understanding of their population dynamics, as well as for the improvement of conservation strategies.

Behavioral ecology is shifting from static models of sex‐role evolution to dynamic frameworks in which demography and behavior form coupled feedback systems. Here, we outline a unifying approach developed at the University of Bath—the demographic feedback model —that links individual decisions to population structure through the adult sex ratio (ASR), a measurable demographic variable that integrates survival, maturation, and reproduction. Across species, sex‐biased survival and remating opportunities generate a recursive feedback between mating systems, parental care, and sexual dimorphism. This feedback, in turn, shape population viability and conservation outcomes. By embedding ASR monitoring within long‐term field studies and comparative phylogenetic analyses, our research reveals how demographic distortions propagate through social behavior, and how behavior feeds back to restructure demography. The resulting feedback framework connects behavioral ecology, life‐history theory, and conservation demography under a single logic: populations evolve not through linear causation, but through nested feedbacks linking genes, ecology, and behavior. We identify four key frontiers—cross‐taxon field protocols, causal comparative inference, nested‐feedback theoretical modelling, and integration with biodiversity conservation practice—that will define the next generation of research. Recognizing behavior as both a product and a driver of demographic structure opens a path toward a genuinely recursive theory of evolution.