Lining the nest with more feathers increases offspring recruitment probability: Selection on an extended phenotype in the blue tit

Previous reproductive success informs nest-building decisions

Behavioral outcomes, including foraging efficiency and reproductive success, often improve with age and with repeated breeding attempts. Here we examined the role of previous experience on the nest-building behavior of wild blue tits Cyanistes caeruleus. In particular, we focused on how previous success or failure in rearing nestlings shapes nest-building decisions in subsequent years. We found that previous breeding outcome is important for predicting nest building decisions in blue tits: birds that had previously raised fledglings added insulating material at a similar rate as they had when they built their first nest. Some birds that had been previously unsuccessful changed their rate of adding insulating material and then were more likely to produce fledglings. These responses indicate that at least some of the decisions made by wild nest-building birds are based on their own experience of past breeding seasons.

Pollution-related changes in nest microbiota: Implications for growth and fledging in three passerine birds

Non-ferrous smelters emit toxic metals into the environment, posing a threat to wildlife health. Despite the acknowledged role of microbes in host health, the impact of such emissions on host-associated microbiota, especially in wild birds, remains largely unexplored. This study investigates the associations of metal pollution, fitness, and nest microbiota (serving as a proxy for early-life microbial environment) which may influence the nestling health and development. Our study focuses on three passerine birds, the great tit (Parus major), blue tit (Cyanistes caeruleus), and pied flycatcher (Ficedula hypoleuca), within control and metal-polluted sites around a Finnish copper-nickel smelter. The polluted sites had been contaminated with arsenic (As), cadmium (Cd), copper (Cu), nickel (Ni), and zinc (Zn). We performed bacterial 16S rRNA sequencing and metal analyses on 90 nests and monitored nestling body mass, fledging success, and various biotic and abiotic factors. Our findings revealed species-specific responses to metal exposure in terms of both fitness and nest microbiota. P. major and C. caeruleus showed sensitivity to pollution, with decreased nestling growth and fledging in the polluted zone. This was accompanied by a shift in the bacterial community composition, which was characterized by an increase in some pathogenic bacteria (in P. major and C. caeruleus nests) and by a decrease in plant-associated bacteria (within C. caeruleus nests). Conversely, F. hypoleuca and their nest microbiota showed limited responses to pollution, indicating greater tolerance to pollution-induced environmental changes. Although pollution did not correlate with nest alpha diversity or the most abundant bacterial taxa across all species, certain potential pathogens within the nests were enriched in polluted environments and negatively correlated with nestling fitness parameters. Our results suggest that metal pollution may alter the nest bacterial composition in some bird species, either directly or indirectly through environmental changes, promoting pathogenic bacteria and potentially impacting bird survival.

Beak shape and nest material use in birds

The evolution of behaviour can both influence, and be influenced by, morphology. Recent advances in methods and data availability have facilitated broad-scale investigations of physical form and behavioural function in many contexts, but the relationship between animal morphology and object manipulation-particularly objects used in construction-remains largely unknown. Here, we employ a new global database of nest materials used by 5924 species of birds together with phylogenetically informed random forest models to evaluate the link between beak shape and these nest-building materials. We find that beak morphology, together with species diet and access to materials, can predict nest-material use above chance and with high accuracy (68-97%). Much of this relationship, however, is driven by phylogenetic signal and sampling biases. We therefore conclude that while variation in nest material use is linked with that of beak shape across bird species, these correlations are modulated by the ecological context and evolutionary history of these species. This article is part of the theme issue 'The evolutionary ecology of nests: a cross-taxon approach'.

Why do some bird species incorporate more anthropogenic materials into their nests than others?

Many bird species incorporate anthropogenic materials (e.g. sweet wrappers, cigarette butts and plastic strings) into their nests. Anthropogenic materials have become widely available as nesting materials in marine and terrestrial environments globally. These human-made objects can provide important benefits to birds such as serving as reliable signals to conspecifics or protecting against ectoparasites, but they can also incur fundamental survival and energetic costs via offspring entanglement and reduced insulative properties, respectively. From an ecological perspective, several hypotheses have been proposed to explain the use of anthropogenic nest materials (ANMs) by birds but no previous interspecific study has tried to identify the underlying mechanisms of this behaviour. In this study, we performed a systematic literature search and ran phylogenetically controlled comparative analyses to examine interspecific variation in the use of ANM and to examine the influence of several ecological and life-history traits. We found that sexual dimorphism and nest type significantly influenced the use of ANMs by birds providing support for the 'signalling hypothesis' that implies that ANMs reflect the quality of the nest builder. However, we found no support for the 'age' and 'new location' hypotheses, nor for a phylogenetic pattern in this behaviour, suggesting that it is widespread throughout birds. This article is part of the theme issue 'The evolutionary ecology of nests: a cross-taxon approach'.

Tits (Paridae sp.) use social information when locating and choosing nest lining material

Abstract 

As an important determinant of reproductive success, avian nest building is under strong selection and requires behavioral plasticity to optimize conditions in which offspring develop. Learning is a one form of plasticity that allows adaptation to the local environment. Birds may refine nest-building behavior with personal experience or use social information to guide their choices. While there is mounting evidence for an effect of experience-based learning on nest building and social information use when selecting nesting material in the laboratory, experimental evidence for social information use in wild birds is lacking. Here, we provided sources of two differently colored wool as nest lining material in a wild mixed-species community of tits (Paridae sp.) to investigate experimentally (i) whether females use social information to locate lining materials and (ii) whether preferences for specific materials (here color) are socially influenced. We investigated pathways of social transmission through a foraging association and a spatial breeding network using the time of arrival at the wool in a network-based diffusion analysis. Our results gave evidence that birds learned about the location of lining resources from foraging associates. Furthermore, we found significant non-random clustering of wool colors in nest boxes across the study area, suggestive of a social influence on selecting lining materials. Taken together, we provide quantitative evidence for a role of social information use in both finding and selecting lining material in wild tits and demonstrate that social information use constitutes an important factor towards behavioral plasticity in nest building in wild birds.

Significance statement

As vessels of reproduction, avian nests are under strong selection to provide optimized conditions for developing offspring. Learning is one mechanism that allows individuals to adapt to local environmental conditions. Previous work has shown that nest-building birds use both social information and personal experience to refine their nests. Yet, evidence for social information use for nest construction in the wild has been purely anecdotal and experimental evidence lacking. Here, we demonstrate for the first time experimentally that in wild tits (Paridae sp.), females rely on social information from their foraging associates to locate and choose material to line their nests. This research highlights the importance of social information use as a potential mechanism of behavioral plasticity in wild nest-building birds.

The significance of building behavior in the evolution of animal architecture

Animals make a diverse array of architectures including nests, bowers, roosts, traps, and tools. Much of the research into animal architecture has focused on the analysis of physical properties such as the dimensions and material of the architectures, rather than the behavior responsible for creating these architectures. However, the relationship between the architecture itself and the construction behavior that built it is not straightforward, and overlooking behavior risks obtaining an incomplete or even misleading picture of how animal architecture evolves. Here we review data about animal architectures broadly, with a particular focus on building by birds and social insects. We then highlight three ways in which a better understanding of building behavior could benefit the study of animal architecture: by clarifying how behavior leads to physical properties; by examining the costs and benefits of building behavior; and by determining the role of learning and how this interacts with selection on behavior. To integrate questions about building behavior alongside those about architectures, we propose a framework inspired by Niko Tinbergen's four questions, examining the mechanistic, ontogenetic, phylogenetic, and functional basis of animal building. By integrating the study of behavior and architecture across levels of analysis, we can gain a more holistic view of the behavior-architecture interactions, and a better understanding of how behavior, cognition, and evolution interact to produce the diversity seen in animal architecture.

Nest decoration: birds exploit a fear of feathers to guard their nest from usurpation

Many species of birds incorporate feathers into their nest as structural support and to insulate the eggs or offspring. Here, we investigated the novel idea that birds reduce the risk of nest usurpation by decorating it with feathers to trigger a fear response in their rivals. We let prospecting birds choose between a dyad of nest-boxes in the wild, both containing some nest materials, but where one had a few white feathers and the other had none. All three species of cavity-nesting birds studied, the pied flycatcher Ficedula hypoleuca, the blue tit Cyanistes caeruleus, and the tree swallow Tachycineta bicolor, hesitated to enter boxes with white feathers. A similar avoidance of white feathers was found when the alternative nest-box of a dyad held black feathers. However, the birds readily collected white feathers that we placed in front of their nest-box, showing the fear of such feathers was context-dependent. We suggest that naive prospecting birds may perceive feathers in nests as the result of a predation event, and that owners decorate nests with bright feathers that can be seen from the opening to deter others from entering.