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Summary Nest structure is thought to provide benefits that have fitness consequences for several taxa. Traditionally, reduced nest predation has been considered the primary benefit underlying evolution of nest structure, whereas thermal benefits have been considered a secondary or even non‐existent factor. Yet, the relative roles of these factors on nest structures remain largely unexplored. Enclosed nests have a constructed or natural roof connected to sides that allow a restricted opening or tube entrance that provides cover in all directions except the entrance, whereas open nests are cups or platforms that are open above. We show that construction of enclosed nests is more common among songbirds (Passeriformes) in tropical and southern hemisphere regions than in north temperate regions. This geographic pattern may reflect selection from predation risk, under long‐standing assumptions that nest predation rates are higher in southern regions and that enclosed nests reduce predation risk compared with open cup nests. We therefore compared nest predation rates between enclosed vs. open nests in 114 songbird species that do not nest in tree holes among five communities of coexisting birds, and for 205 non‐hole‐nesting species from the literature, across northern temperate, tropical, and southern hemisphere regions. Among coexisting species, enclosed nests had lower nest predation rates than open nests in two south temperate sites, but not in either of two tropical sites or a north temperate site. Nest predation did not differ between nest types at any latitude based on literature data. Among 319 species from both our field studies and the literature, enclosed nests did not show consistent benefits of reduced predation and, in fact, predation was not consistently higher in the tropics, contrary to long‐standing perspectives. Thermal benefits of enclosed nests were indicated based on three indirect results. First, species that built enclosed nests were smaller than species using open nests both among coexisting species and among species from the literature. Smaller species lose heat fastest and thereby may gain important thermal benefits from reduced convective cooling. Second, eggs were warmed by parents for less time in species with enclosed nests, as can be expected if egg cooling rates are slower. Finally, species using enclosed nests exhibited enhanced growth of mass and wings compared with species using open nests, suggesting reduced thermoregulatory costs allowed increased energy for growth. Enclosed nests may therefore provide more consistent thermal than nest predation benefits, counter to long‐standing perspectives. A lay summary is available for this article. Lay Summary

Abstract In animals, species differ remarkably in parental care strategies. For instance, male-only care is prevalent in teleost fishes, while biparental care predominates in birds and female-only care is widespread in mammals. Understanding the origin and maintenance of diversified parental care systems is a key challenge in evolutionary ecology. It has been suggested that ecological factors and life-history traits play important roles in the evolution of parental care, but the generality of these predictions has not been investigated across a broad range of taxa. Using phylogenetic comparative analyses and detailed parental care data from 1101 avian species that represent 119 families of 26 orders, here we investigate whether parental strategies are associated with ecological variables (i.e., food type, nest structure, and coloniality) and life-history characteristics (i.e., chick development mode and body size). We show that parental care strategies are in relation to coloniality (solitary, semi-colonial, colonial) and chick development mode (altricial vs. precocial). Colonial and altricial species provide more biparental care than solitary and precocial species, respectively. In contrast, food type (plant, invertebrate, vertebrate), nest structure (open vs. closed), and body size do not covary systematically with parental care patterns in birds. Taken together, our results suggest that living in groups and/or having high-demand offspring are strongly associated with biparental care. Towards the end, we discuss future research directions for the study of parental care evolution.Significance statementAnimal species differ remarkably in the amount of care parents provide to their offspring and in the distribution of care tasks over the parents. In birds, for example, the young of some species are quite independent from the start, while the young of other species are helpless after hatching, requiring a lot of care. Moreover, either the female or the male does most of the caring in some species, while the parental tasks are shared equally in still other species. To understand the diversified parental care patterns, we applied advanced comparative methods to a large data set comprising over 1000 bird species. The analysis reveals that the parents tend to share their care duties equally when they live in groups and/or have offspring that are born helpless, and that parental care patterns are not associated with diet, nest type or body size. Hence, living in groups and having high-demand offspring seem to play important roles in the evolution of parental care.

Offspring mortality varies dramatically among species with critical demographic and evolutionary ramifications, yet the causes of this variation remain unclear. Nests are widely used for breeding across taxa and thought to influence offspring mortality risk. Traditionally, more complex, enclosed nest structures are thought to reduce offspring predation by reducing the visibility of nest contents and muffling offspring sounds compared to open nests. Direct tests of the functional bases for nest structure influence on predation risk are lacking. We used experiments and 10 years of observational data to examine how nest structure influences nest predation risk in a diverse community of tropical songbirds. First, we examined how nest size was related to nest structure and nest predation rates across species. Second, we assessed how nest structure influences the detectability of nestling begging calls both in field and in laboratory settings. Finally, we examined how the acoustic properties of different nest structures influence nest predation risk. Specifically, we experimentally broadcast begging calls from open and enclosed nests to determine how auditory cues and nest structure interact to affect predation on plasticine and quail eggs. We also tested whether nest structure was associated with differences in nest predation rates between the incubation (no begging cues) and nestling (begging cues) stages. We found that enclosed nests are larger than open nests after accounting for adult size, and larger nests had increased predation rates. Moreover, enclosed nests did not consistently alter nestling begging calls in ways that reduce the likelihood of predation compared to open nests. Indeed, begging cues increased predation rates for enclosed but not open‐cup nests in our playback experiment, and nest predation rates showed greater increases after hatching in enclosed than open‐cup nests. Ultimately, enclosed nests do not necessarily provide greater predation benefits than open nests in contrast to long‐standing theory. A free plain language summary can be found within the Supporting Information of this article. A free Plain Language Summary can be found within the Supporting Information of this article.

Despite the accumulation of structural descriptions of bird nests and considerable diversity in these structures across species, we know little about why birds build the nests that they do. Here we used phylogenetic comparative analyses to test one suggested explanation, specifically for Old World babblers (Timaliidae): that building a domed nest coevolved with building a nest on the ground. We show that babblers that build domed nests build them at a lower height than do babblers that build cup-shaped nests, and that in this radiation the evolution of domed nests depended on the transition to building a nest on the ground. Our results are consistent with the hypothesis that babblers add a roof to the nest in order to confer protection against increased predation risk on the ground. We believe that this is the first formal identification of evolutionary pathways that have led to the diversity in nest structure and location that we see today.

Reproductive success is an important demographic parameter that can be driven by environmental and behavioural factors operating on various spatio‐temporal scales. As seabirds breed on land and forage in the ocean, processes occurring in both environments can influence their reproductive success. At various locations around East Antarctica, Adélie penguins' (Pygoscelis adeliae) reproductive success has been negatively linked to extensive sea‐ice. In contrast, our study site in the Windmill Islands has limited fast ice present during the breeding season, allowing us to examine drivers of reproductive success under vastly different marine environmental conditions. Here, we examined the reproductive success of 450 Adélie penguin nests over a 10‐year period using images obtained from remotely operated cameras. We analysed nest survival in relation to marine and climatic factors, environmental conditions at the camera site and immediately around the nest, and behavioural attributes reflecting parental investment and phenological timing. Our key result was a strong positive association between nest structure and chick survival, particularly when ground moisture and snow cover around the nest were high. Earlier nesting birds were more likely to build bigger nests, although it is unclear whether this is due to more time available to build nests or whether early arrival and high‐quality nests are complementary traits. This intrinsic activity is likely to become more important if future predictions of increased snowfall in this region manifest. In the Windmill Islands, it is not well‐known what drives Adélie penguin reproductive success. Here, we utilised remotely operated cameras to determine the drivers of this and found that adult behaviour largely influences nest survival and reproductive success.

Aim: The laying of eggs and the building of a nest structure to accommodate them are two of the defining characteristics of members of the class Aves. Nest structures vary considerably across avian taxa and for many species the structure of the completed nest can have important consequences both for parents and their offspring. While nest characteristics are expected to vary adaptively in response to environmental conditions, large-scale spatial variation in nest characteristics has been largely overlooked. Here, we examine the effects of latitudinal variation in spring temperatures on nest characteristics, including insulatory properties, and reproductive success of blue tits, Cyanistes caeruleus, and great tits, Parus major. Location: Great Britain. Methods: Nests and reproductive data were collected from seven study sites, spread over 5° of latitude. The nest insulatory properties were then determined before the nests were separated into nest base material and cup lining material. Results: As spring temperatures increased with decreasing latitude, the mass of the nest base material did not vary in either species, while the mass of the cup lining material and nest insulatory properties decreased in both species. This suggests that in response to increasing temperatures the breeding female reduces the mass of the cup lining material, thereby maintaining an appropriate microclimate for incubating and brooding. The mean first egg date of both species advanced with decreasing latitude and increasing spring temperatures, although clutch size and brood size at hatching and fledging did not vary. Main conclusions: This is the first study to demonstrate that the nestconstruction behaviour of birds varies in response to large-scale spatial variation in ambient temperatures. Therefore, nest composition reliably indicates environmental conditions and we suggest that studies of nest structure may be sentinels for the early signs of rapid climate change.

Eresus kollari is typically found in dry grasslands and stony steppes; however, in South Korea, it has been primarily found in the humid environments of cemeteries. These spiders have highly localized habitats, and their burrowing and nest‐building habits make them difficult to find and observe in the field. This study investigated the cemetery habitat environment, which has not been well‐researched previously. Because direct observation without separating the spiders from their nests is difficult, the relationship between nest size and individual size was studied to estimate the size of the spiders based on their nests. The cemeteries are open and sunny, with loess‐like soil. The ground surface is mainly covered with Korean lawn grass, lacking trees or shrubs, and the herbaceous layer consists of low‐growing plants. The nests of E. kollari consist of an aboveground web canopy and an underground retreat, and they were found just below the grass. The height of the web canopy and the depth of the retreat were not correlated with the individuals' body size. However, the overall nest diameter exhibited a positive exponential relationship with both cephalothorax and abdomen size. In particular, the product of cephalothorax width and length was the most informative parameter for predicting nest diameter. Remains of beetles and ants were found in the web canopy, suggesting that these insects constitute the primary prey of E. kollari. However, in the case of very small ants, it seems that Plagiolepis manczshzurica may be a predator of E. kollari, as ants were found alongside E. kollari remains within the nest. In South Korea, E. kollari is not designated as an endangered species, but its habitat and population have reportedly been in decline. Notably, the habitat observed during the study period was destroyed by construction activities. Therefore, research and conservation measures for this species are necessary.

Ants are ancient animals on the earth and are known as excellent architects in the animal kingdom. The structure and performance of their nests are full of remarkable mysteries. At present, there are only a limited number of studies on the ventilation performance of underground ant nest structures. In this study, the nests of Camponotus japonicus Mayr were collected manually, and a three-dimensional digital model of the ant nest structure was obtained by the method of industrial CT scanning. The ventilation performance of the Camponotus japonicus Mayr nest structure was numerically simulated using the finite element analysis software, FLUENT. By changing the air inlet and outlet of the nest, the pressure changes inside the nest and the trajectory of the air flow inside the nest could be calculated and analysed, in order to explore the ventilation characteristics of the underground nest structure during natural ventilation. It was found that the ventilation environment inside the nest was stable, and that the external air flow had little effect on the life of the ants inside the nest.

Background Nest construction is a key element of avian reproductive behaviour and the result is often a complex structure that is used for incubation of eggs, which represents an extended phenotype. It is known that nest construction is a plastic behaviour but the extent to which plasticity is observed in a single species with a wide geographical distribution is largely unknown. This study sought to better understand variation in nest size and composition across a very wide geographical area. The hypothesis suggested that location would affect size but not composition of nests of the European Pied Flycatcher ( Ficedula hypoleuca ). Methods Nests and reproductive data were collected from seventeen study sites, spread over 6° of latitude and 3.3° of longitude on the island of Great Britain. Dimensions of nests were measured before they were deconstructed to determine the masses and types materials used in the outer nest and the cup lining. Results Geographical variation was observed in base thickness of nests but not many other dimensions. Nests varied in composition but were mainly made of leaf, moss, bark, grass, root and fern. Moss was used more to the north and east of the study area compared with more leaf mass towards the south and west. The species of leaf and bark used in the nests varied between geographical locations. Additionally, the use of leaves or bark from a particular tree species did not reflect the incidence of the tree species in the immediate territory. Conclusions This study showed that nest composition was affected by geographical location over a wide area. Variation between nests at each location was high and so it was concluded that differences in nest composition reflect individual selection of materials but evidence is such that it remains unclear whether this is deliberate to fulfil a specific role in the nest, or simply opportunistic with birds simply picking up materials with the appropriate characteristics as they find them outside their nestbox.

Maintaining avian eggs and young at optimum temperatures for development can increase hatching success and nestling condition, but this maintenance requires parental energetic demands. Bird nests, which often provide a structure to safely hold the eggs and nestlings and protect them from predators, can additionally be designed to help maintain eggs’ optimum temperatures by minimising heat loss, especially in climates where eggs cool rapidly when unattended. We collected and measured Prairie Warbler (Setophaga discolor) nests in western Massachusetts, U.S. in 2009 and conducted a climate-controlled, nest-cooling experiment to determine how nest characteristics affect thermal properties for small, open-cup nesting birds. We then assessed if nests with better insulation properties resulted in any fitness benefits, and also tested if nest structural characteristics affected birds’ fitness. We found that nest characteristics influenced their thermal properties, with thicker, heavier, and larger nests having slower cooling rates and higher predicted equilibrium egg temperatures. Both nest cup depth and clutch size significantly declined over the breeding season, and we observed a trend, although non-significant, that nests with shallower cups had smaller clutches. Contrary to studies on cavity-nesting birds, we found no significant effects of nest thermal properties or nest structure on hatching and fledging success, nestling condition, brood parasitism, or nest survival. Prairie Warblers in our study site may already be adapted to build nests within a range that maximises their fitness. Furthermore, studies have shown that open-cup nests of other species are relatively thicker and more insulated in colder environments at higher latitudes than our study. Instead of building nests to solely minimise heat loss, open-cup nesting birds in temperate climates may also be driven by opposing selection pressures when building their nests, such as to prevent nestlings from overheating during hot days.