Evolution of parental activity at the nest is shaped by the risk of nest predation and ambient temperature across bird species

Coordination of parental performance is breeding phase-dependent in the Dovekie (Alle alle), a pelagic Arctic seabird

Currently, parental care is becoming increasingly perceived as male and female cooperation, instead of being primarily shaped by sexual conflict. Most studies examining cooperating performance consider coordination of parental activities, and doing so focuses on a short time-window including only one stage of breeding (i.e., incubation or chick rearing period). Here, we considered the cooperation of breeding partners, investigating the coordination of parental care in a long-lived seabird species with long and extensive biparental care, the Dovekie (or Little Auk), Alle alle, and looked at the issue throughout the breeding season. Previous studies on this species revealed coordinated chick provisioning, but parental coordination during incubation remains unstudied. Using video recordings collected over the course of two breeding seasons, we tested whether coordination was subject to small-scale changes within each stage and whether there was a relationship between coordination levels across the two stages. We found that the level of parental coordination is overall high and increases during the incubation period but decreases through the chick rearing phases. There were some inter-annual differences in the coordination level both at the incubation and chick rearing stages. We also found some dependency between the coordination during the incubation and chick rearing periods. All these results suggest that coordination is not a fixed behavior but breeding-phase dependent. The present study thus provides insights into how parental care and parents' cooperation is shaped by brood needs and conditions. It also highlights a relationship between coordination levels during chick rearing and incubation periods, suggesting some extent of temporal dependence in coordination of parental performance within the breeding season.

Comparative reproductive ecology of Old and New World Trogons, an order in decline across the world

Many tropical species show declining populations. The pantropical order Trogoniformes has 76% of its species ranked as declining, reflecting a worldwide problem. Here, we report on the reproductive ecology and life history traits of the declining and near-threatened old world Whitehead's Trogon (Harpactes whiteheadi), the declining new world Collared Trogon (Trogon collaris), and the stable Masked Trogon (T. personatus). We also reviewed the literature on reproductive ecology and life history traits of trogons to assess possible commonalities that might help explain population declines. We found that the declining Whitehead's and Collared Trogons had reasonable nest success (32% and 25%, respectively), while the stable Masked Trogon had poor reproductive success (9%), all contrary to population trends. However, the limited literature data suggested that poor reproductive success may be common among trogons, which may contribute to population declines. Parents fed young at a low rate and had long on-bouts for incubation and nestling warming that reduced activity at the nest, as favored by high nest predation risk over evolutionary time. We found that young fledged from the nest with poorly developed wings, as also favored by high nest predation risk. Evolved nestling periods among trogon species suggests that poor wing development is likely common. Wing development has been shown to affect juvenile survival after leaving the nest. The poor wing development may be an important contributor to population declines that deserves more attention. Evolved life history traits are important to recognize as creating population vulnerabilities in a changing world.

Comparison of Reproductive Strategies between Two Sympatric Copsychus Passerines

Reproduction plays a crucial role in determining the development, fate, and dynamics of bird populations. However, reproductive strategies vary among species and populations. In this study, we investigated the reproductive strategies of the Oriental Magpie Robin (Copsychus saularis) and White-rumped Shama (C. malabarica), which are closely related passerines that reproduce in sympatric areas. We found that although these two species were both cavity nesting, their nest-site selection differed; the Shama preferred nesting close to trees and forests, whereas the Magpie Robin nested close to human residential areas. Furthermore, their egg incubation patterns differed; the Shama increased daily incubation frequency with incubation time, but the Magpie Robin maintained its daily incubation time regardless of changes in incubation frequency. However, the nestling heating patterns of these two species were similar, indicating a critical demand for regulating hatchling body temperature during this crucial stage. The feeding frequencies of male parents were strongly correlated with those of females in both species, suggesting equal contribution and good synchronization between the sexes. Nestling feeding frequency was also correlated with nest cleaning frequency, implying coordination between feeding and defecation by parents and offspring, respectively. This research explored the divergence and convergence of reproductive strategies between these two sympatric species, providing valuable insights into the niche differentiation theory.

Sex differences in avian parental care patterns vary across the breeding cycle

Parental care in birds consists of elaborate forms across stages, including nest building, incubation, and offspring provision. Despite their evolutionary importance, knowledge gaps exist in the extent to which parents contribute disproportionately to these forms and factors that are associated with variations in care patterns between sexes. Here, we analyzed 1533 bird species and discovered remarkable variability in care patterns. We show that parental care should not be viewed as a unitary trait but rather as a set of integrated features that exhibit considerable temporal and sex-specific variation. Our analyses also reveal moderate consistency in care patterns between breeding stages, pointing towards shared intrinsic factors driving sex-specific care. Notably, we found that species experiencing strong sexual selection on males or species facing paternity uncertainty display a tendency towards female-biased care. This work advances our understanding of the temporal variations in sex-specific contributions to avian parental care and their potential evolutionary drivers.

Convergent evolution of elaborate nests as structural defences in birds

The pendent nests of some weaverbird and icterid species are among the most complex structures built by any animal, but why they have evolved remains to be explained. The precarious attachments and extended entrance tunnels characteristic of these nests are widely speculated to act as structural defences against invasion by nest predators, particularly tree-climbing snakes, but this hypothesis has yet to be systematically tested. We use phylogenetic comparative methods to investigate the relationship between nest structure and developmental period length, a proxy for offspring mortality, in weaverbirds (Ploceidae) and icterids (Icteridae), two bird families in which highly elaborate pendent nests have independently evolved. We find that more elaborate nests, particularly those with entrance tunnels, are associated with longer developmental periods in both families. This finding is robust to potentially confounding effects of body mass, phylogenetic relationships, nest location and latitude. Our results are consistent with the hypothesis that elaborate nest structures in birds can function as structural defences, resulting in lower offspring mortality and slower development. More generally, our findings suggest that constructing complex, protective structures may buffer against environmental hazards, reducing extrinsic mortality and contributing to the evolution of slower life histories in diverse animal lineages, even humans.

Weather impacts on interactions between nesting birds, nest-dwelling ectoparasites and ants

Weather has a dominant impact on organisms, including their life histories and interspecific interactions. Yet, for nesting birds, and the arthropods inhabiting bird nests, the direct and cascading effects of weather are poorly known. We explored the influence of ambient temperatures and rainfall on the cohabitation of dome-shaped bird nests by Wood Warblers Phylloscopus sibilatrix, their blowfly Protocalliphora azurea ectoparasites, and predatory Myrmica and Lasius ants that may provide nest sanitation. We sampled blowflies and ants in 129 nests, and measured warbler nestlings during 2018-2020 in the primeval Białowieża Forest, eastern Poland. The probability of ectoparasites occurring in nests increased with increasing ambient temperatures and declining precipitation in the early nestling stage, when adult blowflies are ovipositing. Where present, the number of ectoparasites was greater if higher ambient temperatures had prevailed in the late nestling stage, but only when ants were absent from nests. However, the nestling growth was unrelated to ectoparasite abundance or ant presence within bird nests, although it was lower at high rainfall. The results suggest that weather can have conflicting impacts on interactions between nesting birds and nest-dwelling arthropods, but birds can mostly compensate for any related costs in old-growth forest, where food is generally abundant.

Nest density, egg conspicuity, vegetation structure and seasonality affect artificial nest predation in the Brazilian Cerrado

Nest predators use visual, acoustic and chemical cues to locate nests. In the Neotropics, predation is high being the main cause of nest failure. Despite that, it is still not completely clear what kind of information predators are using to find nests or whether predators respond differently according to habitat characteristics. Here, we executed an experimental manipulation to investigate how different ecological factors influence nest predation probability. We hypothesised that egg conspicuousness, nest clustering and a more open vegetation structure would increase nest predation probability, and that nest predation would be higher during the breeding season of most avian species in the region. We used artificial nests baited with plasticine and quail eggs (Coturnix coturnix), manipulated egg coloration and nest density. Artificial nests were distributed over forest and savanna-like vegetations. Overall predation rate was 40.9%. We found that nests baited with conspicuous eggs, located in open habitats, at higher densities and during the dry period were more predated. Results suggest that main predators must be visually orientated, and that egg crypsis is an important trait for open-nest species in the area. Moreover, a higher nest density may affect predator behaviour, favouring an increase in nest searching, which may be facilitated in open habitats.

Nest architecture is linked with ecological success in songbirds

Nests are essential constructions that determine fitness, yet their structure can vary substantially across bird species. While there is evidence supporting a link between nest architecture and the habitat a species occupies, we still ignore what ecological and evolutionary processes are linked to different nest types. Using information on 3175 species of songbirds, we show that-after controlling for latitude and body size-species that build domed nests (i.e. nests with a roof) have smaller ranges, are less likely to colonise urban environments and have potentially higher extinction rates compared to species with open and cavity nests. Domed nests could be a costly specialisation, and we show that these nests take more time to be built, which could restrict breeding opportunities. These diverse strands of evidence suggest that the transition from domed to open nests in passerines could represent an important evolutionary innovation behind the success of the largest bird radiation.

Being the Winner Is Being the Loser When Playing a Parental Tug-of-War – A New Framework on Stability of Biparental Care

Because there are basic sexual differences in reproductive potential, and the cost of parental care is assumed to be high, biparental care is viewed as a constant tug-of-war between the partners. This raises the question of the system’s evolutionary stability. Several models have been proposed to resolve this problem but none has received unequivocal support. Here, I propose a framework that not only integrates the earlier theoretical ideas (sealed bids, negotiation) but also considers the importance of the environment (frequently neglected in previous models) and views the cost of parental care from a different perspective (costly in terms of parent’s survival only when performed close to the boundary of parental capacity). The framework suggests that sexual conflict may not be such a significant factor mediating parental care as commonly assumed, and that a parent trying to shift the parental burden onto the partner – assumed to be the winner in the tug-of-war interplay – is actually more likely to be a loser, as doing so may put the success of the current breeding attempt in jeopardy, thereby reducing overall fitness of the parent. Once it is realized that the importance of sexual conflict is actually much less than it seems, it becomes clear that the stability of the biparental care system no longer seems to be such a puzzling issue.

Task division in a facultative cooperative breeder bird: do males take out the trash?

Cooperative animals share different activities during reproduction, but individuals of a social group may invest in these tasks in different proportions. Nest sanitation is an important task that may impact reproductive performance of birds, and yet, little is known about the relative participation of individuals of a social group, particularly in non-passerine species. Here, we describe nest sanitation behaviour and materials removed, and test the occurrence of task division regarding faecal sac removal in Campo flickers (Picidae), a facultative cooperative breeder with complex social system. We found that helpers removed proportionally more faecal sacs than breeders, and male helpers are mainly responsible for this activity. These results are different than the commonly reported patterns for passerines, where females are the main contributors. Different ecological conditions and benefits achieved by group members may influence their investment in nest sanitation, but additional studies on social species could greatly contribute to our understanding of how general our results are in non-passerine species.

Climate as an Evolutionary Driver of Nest Morphology in Birds: A Review

Avian nests are critical for successful reproduction in birds. Nest microclimate can affect egg development, chick growth and fledgling success, suggesting that nest building behavior should be under strong selective pressure to nesting conditions. Given that the internal microclimate of the nest is critical for avian fitness, it is expected that nest morphology is shaped by the local environment. Here we review the relationship between nest morphology and climate across species’ distributions. We collate growing evidence that supports a link between environmental conditions and particular nest traits, within species and across species. We discuss the degree to which phenotypic plasticity in nesting behavior can contribute to observed variation in nest traits, the role of phylogenetic history in determining nest morphology, and which nest traits are likely to be influenced by climatic conditions. Finally, we identify gaps in our understanding of the evolution of nest morphology and suggest topics for future research. Overall, we argue that nests are part of the extended phenotype of a bird, they play a crucial role in their reproductive success, and may be an important factor in determining which species will be able to persist in the face of ongoing climate change.

Adaptation and Latitudinal Gradients in Species Interactions: Nest Predation in Birds

AbstractAre biotic interactions stronger in the tropics? Here, we investigate nest predation in birds, a canonical example of a strong tropical biotic interaction. Counter to expectations, daily rates of nest predation vary minimally with latitude. However, life-history traits that influence nest predation have diverged between latitudes. For example, tropical species have evolved a longer average nesting period, which is associated with reduced rates of nest attendance by parents. Daily nest mortality declines with nesting period length within regions, but tropical species have a higher intercept. Consequently, for the same nesting period length, tropical species experience higher daily nest predation rates than temperate species. The implication of this analysis is that the evolved difference in nesting period length between latitudes produces a flatter latitudinal gradient in daily nest predation than would otherwise be predicted. We propose that adaptation may frequently dampen geographic patterns in interaction rates.

Behavioral strategies during incubation influence nest and female survival of Wild Turkeys

Females must balance physiological and behavioral demands of producing offspring with associated expenditures, such as resource acquisition and predator avoidance. Nest success is an important parameter underlying avian population dynamics. Galliforms are particularly susceptible to low nest success due to exposure of ground nests to multiple predator guilds, lengthy incubation periods, and substantive reliance on crypsis for survival. Hence, it is plausible that nesting individuals prioritize productivity and survival differently, resulting in a gradient of reproductive strategies. Fine-scale movement patterns during incubation are not well documented in ground-nesting birds, and the influence of reproductive movements on survival is largely unknown. Using GPS data collected from female wild turkeys (n = 278) across the southeastern United States, we evaluated the influence of incubation recess behaviors on trade-offs between nest and female survival. We quantified daily recess behaviors including recess duration, recess frequency, total distance traveled, and incubation range size for each nest attempt as well as covariates for nest concealment, nest attempt, and nest age. Of 374 nests, 91 (24%) hatched and 39 (14%) females were depredated during incubation. Average nest survival during the incubation period was 0.19, whereas average female survival was 0.78. On average, females took 1.6 daily unique recesses (SD = 1.2), spent 2.1 hr off the nest each day (SD = 1.8), and traveled 357.6 m during recesses (SD = 396.6). Average nest concealment was 92.5 cm (SD = 47). We found that females who took longer recess bouts had higher individual survival, but had increased nest loss. Females who recessed more frequently had lower individual survival. Our findings suggest behavioral decisions made during incubation represent life-history trade-offs between predation risk and reproductive success on an unpredictable landscape.

Adaptation and constraint shape the evolution of growth patterns in passerine birds across the globe

Background

Growth trajectories should be adapted to selective factors of each species’ environment. However, major shaping forces of growth and development are unclear, especially when studying several traits at once. Birds provide an ideal opportunity to analyze growth patterns across species due to there being enough available data. We tested the relative importance of nest predation risk, the number of care-givers, nest height, foraging substrate, clutch size, and latitude on growth patterns of passerine birds (Passeriformes) using phylogenetic comparative methods. Specifically, we studied the evolution of fledging time, average and peak growth rates, and relative development at fledging of body mass and tarsus, wing, and tail length.

Results

Using a comprehensive literature search and data quality control, we obtained data on growth in 231 species based on 295 populations. Species with long development in the nest grew slowly and had well-developed traits at fledging. Species breeding under high nest predation risk, building their nests close to the ground, and those living in northern temperate regions fledged early and grew fast, sometimes fledging with less developed body mass and traits critical for locomotion (tarsus, wing, and tail). On the other hand, the number of caring adults, clutch size, and species’ foraging substrate had very limited predictive value for growth patterns across passerine species.

Conclusions

Shortening of the nestling period was a primary means of accelerating development (in relation to nest predation, nest height, and latitude), sometimes supplemented by higher peak growth rates of body mass, tarsus, and wing (especially in relation to latitude). Overall growth patterns of passerines were adaptively tuned to nest predation risk and nest height, with northern temperate species having especially short nestling periods and fast growth rates of body mass, tarsus, and wing.

Adaptive responses of the embryos of birds and reptiles to spatial and temporal variations in nest temperatures

Natural nests of egg-laying birds and reptiles exhibit substantial thermal variation, at a range of spatial and temporal scales. Rates and trajectories of embryonic development are highly sensitive to temperature, favouring an ability of embryos to respond adaptively (i.e. match their developmental biology to local thermal regimes). Spatially, thermal variation can be significant within a single nest (top to bottom), among adjacent nests (as a function of shading, nest depth etc.), across populations that inhabit areas with different weather conditions, and across species that differ in climates occupied and/or nest characteristics. Thermal regimes also vary temporally, in ways that generate differences among nests within a single population (e.g. due to seasonal timing of laying), among populations and across species. Anthropogenic activities (e.g. habitat clearing, climate change) add to this spatial and temporal diversity in thermal regimes. We review published literature on embryonic adaptations to spatio-temporal heterogeneity in nest temperatures. Although relatively few taxa have been studied in detail, and proximate mechanisms remain unclear, our review identifies many cases in which natural selection appears to have fine-tuned embryogenesis to match local thermal regimes. Developmental rates have been reported to differ between uppermost versus lower eggs within a single nest, between eggs laid early versus late in the season, and between populations from cooler versus warmer climates. We identify gaps in our understanding of thermal adaptations of early (embryonic) phases of the life history, and suggest fruitful opportunities for future research.

Sex roles and the evolution of parental care specialization

Males and females are defined by the relative size of their gametes (anisogamy), but secondary sexual dimorphism in fertilization, parental investment and mating competition is widespread and often remarkably stable over evolutionary timescales. Recent theory has clarified the causal connections between anisogamy and the most prevalent differences between the sexes, but deviations from these patterns remain poorly understood. Here, we study how sex differences in parental investment and mating competition coevolve with parental care specialization. Parental investment often consists of two or more distinct activities (e.g. provisioning and defence) and parents may care more efficiently by specializing in a subset of these activities. Our model predicts that efficient care specialization broadens the conditions under which biparental investment can evolve in lineages that historically had uniparental care. Major transitions in sex roles (e.g. from female-biased care with strong male mating competition to male-biased care with strong female competition) can arise following ecologically induced changes in the costs or benefits of different care types, or in the sex ratio at maturation. Our model provides a clear evolutionary mechanism for sex-role transitions, but also predicts that such transitions should be rare. It consequently contributes towards explaining widespread phylogenetic inertia in parenting and mating systems.

Geographic variation in incubation behavior of a widely distributed passerine bird

Incubating birds must trade-off leaving the nest to forage with staying on the nest to maintain optimal temperatures for developing embryos. This trade-off is expressed through incubation behavior, which can be heavily influenced by climate, food availability, attentiveness of their mates, and nest predation risk. Comparative studies across species have shown that incubation behavior varies across latitude, but few studies have explored how incubation behavior varies across sites within species. We might expect incubation behavior to be flexible and respond to local environmental challenges; alternatively, behavior may be relatively fixed and vary little across a species’ range. We explored four incubation behaviors (male feeding rate, female off-bout duration, female off-bout frequency, and the proportion of time incubating females spent on the nest) in a widespread songbird, the yellow warbler (Setophaga petechia), breeding at a temperate and subarctic site. As temperatures warmed at both sites, males fed females less often, and as male feeding rates decreased, off-bout durations and frequencies increased causing the proportion of time on the nest to decrease. While incubation behaviors changed in similar ways between sites, off-bout durations shortened with increasing male feeding rates most strongly at the temperate site. Overall, these results show flexibility in incubation behaviors in response to different environmental cues, which likely minimize costs associated with provisioning incubating parents and maintaining warm nest temperatures, and suggests that male feeding may be especially important for breeding in cold regions.

Different incubation patterns affect selective antimicrobial properties of the egg interior: experimental evidence from eggs of precocial and altricial birds

Avian eggs contend with omnipresent microorganisms entering the egg interior, where they affect embryo viability and hatchling phenotype. The incubation behaviour and deposition of egg white antimicrobial proteins (AMPs) vary highly across the avian altricial-precocial spectrum. Experimental evidence of how these alterations in avian reproductive strategies affect the antimicrobial properties of the precocial and altricial egg interior is lacking, however. Here, we tested the egg white antimicrobial activity in eggs of two representative model species, from each end of the avian altricial-precocial spectrum, against potentially pathogenic and beneficial probiotic microorganisms. Eggs were experimentally treated to mimic un-incubated eggs in the nest, partial incubation during the egg-laying period, the onset of full incubation and the increased deposition of two main egg white AMPs, lysozyme and ovotransferrin. We moreover assessed to what extent egg antimicrobial components, egg white pH and AMP concentrations varied as a result of different incubation patterns. Fully incubated precocial and altricial eggs decreased their antimicrobial activity against a potentially pathogenic microorganism, whereas partial incubation significantly enhanced the persistence of a beneficial probiotic microorganism in precocial eggs. These effects were most probably conditioned by temperature-dependent alterations in egg white pH and AMP concentrations. While lysozyme concentration and pH decreased in fully incubated precocial but not altricial eggs, egg white ovotransferrin increased along with the intensity of incubation in both precocial and altricial eggs. This study is the first to experimentally demonstrate that different incubation patterns may have selective antimicrobial potential mediated by species-specific effects on antimicrobial components in the egg white.