Latitudinal variation in blue tit and great tit nest characteristics indicates environmental adjustment

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 nest‐construction 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.     

The effects of nest size and insulation on thermal properties of tree swallow nests

The nest environment can have important influences on incubation behavior and nestling development in birds. Nest thermal properties, particularly nest composition and size, can have a major influence on heat loss. To examine the role of nest size and insulation on clutch cooling rates, we collected tree swallow Tachycineta bicolor nests and measured the cooling rate of eggs in a controlled thermal environment. We also examined the thermal benefits of nest feathers by comparing the cooling rates of nests with and without feathers. Nests with more feather insulation and heavier, deeper cupped nests cooled at slower rates. In addition, nests with feathers cooled at much slower rates than did the same nests without feathers. Our results show that nest insulation and size play important roles in nest cooling rates, which may ultimately affect incubation costs and thus reproductive performance.     

Adaptive latitudinal variation in Common Blackbird Turdus merula nest characteristics

Nest construction is taxonomically widespread, yet our understanding of adaptive intraspecific variation in nest design remains poor. Nest characteristics are expected to vary adaptively in response to predictable variation in spring temperatures over large spatial scales, yet such variation in nest design remains largely overlooked, particularly amongst open‐cup‐nesting birds. Here, we systematically examined the effects of latitudinal variation in spring temperatures and precipitation on the morphology, volume, composition, and insulatory properties of open‐cup‐nesting Common Blackbirds’ Turdus merula nests to test the hypothesis that birds living in cooler environments at more northerly latitudes would build better insulated nests than conspecifics living in warmer environments at more southerly latitudes. As spring temperatures increased with decreasing latitude, the external diameter of nests decreased. However, as nest wall thickness also decreased, there was no variation in the diameter of the internal nest cups. Only the mass of dry grasses within nests decreased with warmer temperatures at lower latitudes. The insulatory properties of nests declined with warmer temperatures at lower latitudes and nests containing greater amounts of dry grasses had higher insulatory properties. The insulatory properties of nests decreased with warmer temperatures at lower latitudes, via changes in morphology (wall thickness) and composition (dry grasses). Meanwhile, spring precipitation did not vary with latitude, and none of the nest characteristics varied with spring precipitation. This suggests that Common Blackbirds nesting at higher latitudes were building nests with thicker walls in order to counteract the cooler temperatures. We have provided evidence that the nest construction behavior of open‐cup‐nesting birds systematically varies in response to large‐scale spatial variation in spring temperatures.     

Colour composition of nest lining feathers affects hatching success of barn swallows,Hirundo rustica (Passeriformes: Hirundinidae)

Many bird species use feathers as lining material, and its functionality has traditionally been linked to nest insulation. However, nest lining feathers may also influence nest detection by predators, differentially affect reproductive investment of mates in a post‐mating sexual selection process, and affect the bacterial community of the nest environment. Most of these functions of nest lining feathers could affect hatching success, but the effect might vary depending on feather coloration (i.e. pigmented versus white feathers). This would be the case if coloration is related to: (1) thermoregulatory properties; (2) attractiveness of feathers in the nest for mates; (3) eggshell bacterial density. All of these hypothetical scenarios predict that feathers of different colours would differentially affect the hatching success of birds, and that birds should preferentially choose the most beneficial feather colour for lining their nests. Results from two different experiments performed with a population of Danish barn swallow, Hirundo rustica, were in accordance with these predictions. First, H. rustica preferentially selected white experimentally offered feathers for lining their nests. Second, the experimental manipulation of the feather colour composition of nests of H. rustica had a significant effect on hatching success. Experimental nests with more white feathers added at the beginning of incubation had a lower probability of hatching failures, suggesting differential beneficial effects of lining nests with feathers of this colour. We discuss the relative importance of hypothetical functional scenarios that predicted the detected associations, including those related to sexual selection or to the community of microorganisms associated with feathers of different colours. © 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 102 , 67–74.     

Meta‐analyses of nest predation in temperate Australian forests and woodlands

Nest predation is the leading cause of nesting failure. Thus it is a crucial area of research needed to inform conservation management and to understand the life history of birds. I surveyed the literature to review the identity of nest predators and the factors affecting nest predation, in Australia using 177 studies. Overall, 94 nest predators were identified when incorporating artificial nests, 69 without. Using only natural nests, the Pied Currawong Strepera graculina was the most frequently reported nest predator. Five nest predators, including Pied Currawong, depredated 40% of the prey measured by the number of prey species taken. Yet, 60% of predation was carried out by the other 64 species, which included by the order of importance birds, mammals, reptiles, frogs and ants. Predation at cup and dome nests was more frequently reported than at burrow, ground and hollow nests. Only 28% of predators were observed at both artificial and natural nests suggesting artificial nests have limited, but not negligible, ability as tools for identifying predators. There was a highly significant and positive correlation between predator and prey masses. The predator prey mass ratio was calculated with a mean 0.25 and a median 0.22, a result closely matching with the proportional size of prey taken by raptors. The finding that predator size is proportional to prey opens a pathway for more life history and conservation research.     

Predation risk on incubating adults constrains the choice of thermally favourable nest sites in a plover

Birds are thought to choose nest sites that meet two main functions: providing security to both nest contents and incubating adults, and providing an appropriate microclimate for incubation. Many shorebirds nest in sites with no or little cover. In a lake in southern Spain, nearly 70% of the nests of Kentish plovers, Charadrius alexandrinus, were in sites with little or no cover, where ambient temperatures might be more than 50°C during very hot days, thus causing the incubating adults to suffer from heat stress. We tested the hypothesis that Kentish plovers nest mainly in exposed sites because this may allow the incubating birds to detect approaching predators early, and thus to reduce predation risk. When we occluded the view that incubating adults had from their nests, they took longer to detect approaching predators than when the view was unrestricted. Incubating adults were also more frequently killed by mammals in covered than in exposed nests. Females that nested in covered sites were in lower body condition than those nesting in exposed sites, possibly because they were unable to withstand the high ambient temperatures in exposed sites. Thus, the benefits of thermally favourable nest sites are reduced by the constraints of predation risk.     

Increasing nest predation will be insufficient to maintain polar bear body condition in the face of sea ice loss

Climate change can influence interspecific interactions by differentially affecting species‐specific phenology. In seasonal ice environments, there is evidence that polar bear predation of Arctic bird eggs is increasing because of earlier sea ice breakup, which forces polar bears into nearshore terrestrial environments where Arctic birds are nesting. Because polar bears can consume a large number of nests before becoming satiated, and because they can swim between island colonies, they could have dramatic influences on seabird and sea duck reproductive success. However, it is unclear whether nest foraging can provide an energetic benefit to polar bear populations, especially given the capacity of bird populations to redistribute in response to increasing predation pressure. In this study, we develop a spatially explicit agent‐based model of the predator–prey relationship between polar bears and common eiders, a common and culturally important bird species for northern peoples. Our model is composed of two types of agents (polar bear agents and common eider hen agents) whose movements and decision heuristics are based on species‐specific bioenergetic and behavioral ecological principles, and are influenced by historical and extrapolated sea ice conditions. Our model reproduces empirical findings that polar bear predation of bird nests is increasing and predicts an accelerating relationship between advancing ice breakup dates and the number of nests depredated. Despite increases in nest predation, our model predicts that polar bear body condition during the ice‐free period will continue to decline. Finally, our model predicts that common eider nests will become more dispersed and will move closer to the mainland in response to increasing predation, possibly increasing their exposure to land‐based predators and influencing the livelihood of local people that collect eider eggs and down. These results show that predator–prey interactions can have nonlinear responses to changes in climate and provides important predictions of ecological change in Arctic ecosystems.     

Predation on artificial nests in a forest dominated landscape – the effects of nest type, patch size and edge structure

We studied the effects of forest patch size and forest edge structure on nest predation in a boreal coniferous forest landscape. The following predictions were tested. Nest predation should be higher in small than in large stands, in edges than in interior areas of forest stands, and in barren forest/clear–cut edges created by forestry than in natural forest/open marsh edges. Four types of artificial above ground nests (total of 261) were used; open cup nests with reindeer Rangifer t. tarandus hair, open cup nests with domestic hen Gallus domesticus feathers, and unlined open cup and nest–box nests. Nests were baited with one Japanese quail Coturnix coturnix japonica egg. Nest–boxes were depredated significantly less than open cup nests of all types. No edge- or stand size–related nest predation was found. The predation rate, regardless of the nest type, did not differ relative to the edge type and vegetation characteristics. However, better horizontal visibility of open cup nests due to more open vegetation structure increased predation risk in man–made edges compared to inherent edges. The results suggest that edge–related nest predation is absent or weak in forest dominated landscapes. This may be due to predator types present in the landscape and/or predators habitat use in forest dominated areas. Therefore, it might be that findings documented in other areas, such as in agricultural dominated landscapes, cannot be directly applied to managed forest landscapes.     

Male short-tailed field voles (Microtus agrestis) build better insulated nests than females

Nest construction is an extremely widespread behaviour. In small endotherms the nest serves primarily to provide insulation, and thereby retard heat loss of the constructor, or its offspring. In arctic and temperate regions many small mammals build nests to protect themselves from low ambient temperatures. We measured the physical properties of nests built by short-tailed field voles Microtus agrestis that were kept in captivity under cold conditions. The most important factor influencing nest insulation was nest wall thickness; however, nests with thick walls also contained more nesting material. Insulative capacity of the nest did not reach an asymptote up to nests containing 20 g of material. Nest insulation was not correlated with resting metabolic rate, body mass or body composition of the vole that constructed the nest. However, nests built by males had greater insulation than those made by females; males also had significantly lower food intake rates when compared to females with nests. No significant difference was observed in either fat mass or whole animal thermal conductance between males and females. Thermal conductance did increase significantly with increasing body mass, although not with resting metabolic rate. Voles with nests for prolonged periods had lower food intakes than voles without nests. The absolute saving averaged 1.9 g and was independent of body mass. This was a 28% saving on intake for a 22-g vole but only an 18% saving for a 40-g individual. When voles had nests for short periods they used the energy they saved to reduce food intake and increase body mass. Accepted: 2 September 1999     

Digging beneath the surface: incipient nest characteristics across three species of harvester ant that differ in colony founding strategy

Ants exhibit a size-associated colony founding trait that is characterized by the degree to which foundresses rely on internal reserves to raise their first brood of workers (claustrality). The reliance on stored reserves is positively correlated with degree of claustrality (claustral > facultative > semi-claustral) and is variable across species of Pogonomyrmex harvester ants. Three species of harvester ant foundresses that differ in degree of claustrality were observed initiating nests under laboratory conditions over 2 years. P. rugosus is fully claustral, P. salinus is facultative, and P. californicus is semi-claustral. Across species, degree of claustrality was positively associated with mean digging rate and nest depth over the first 3 days of nest initiation, total nest depth, and degree of nest closure. Branching and abundance of peripheral nodes were higher in semi-claustral and facultative nests than in claustral nests. The facultative species dug for the longest time and achieved the greatest tunnel length. Within each species, there were trends associating mass with digging rate, but these were not consistent in all species. There were no intraspecific trends of mass with nest depth. Also within species, a foundress’s mass did not affect her tendency to open or close her nest. These results reveal degree of claustrality is correlated across species with several nest initiation characteristics that together may represent different colony founding syndromes.     

On the evolution of clutch size and nest size in passerine birds

Summary I examined the hypothesis that the clutch size of some altricial birds may be limited by over-crowding of the nestlings in the nest, by comparing data on different species of European passerines. Large-sized birds build, relative to the body, larger nests than small-sized birds, both as regards the inner and the outer nest widths and as regards edge breadth; only inner nestcup depth did not change relatively to body size. Nest size also varied in relation to nesting place. Birds with open nests built off the ground had a rather narrow nestcup, whereas those with a domed nest, or which nest in a cavity, had a wide nestcup. When only open-nesters were compared, birds nesting on, or close to, the ground tended to have a wider nestcup than birds nesting above the ground. Inner nestcup width was correlated with the amount of mosses and lichens used in building the nest; the more of such materials the narrower the nestcup. The three variables: standardised body size, nesting place, and type of nesting material used accounted for 92% of the overall variation observed in inner nestcup width. When controlling for adult body size, clutch size was positively correlated with the size of the nestcup. A multiple regression analysis showed that relative nestcup depth, nest site, and type of nesting materials used, accounted for 64% of the overall variation in clutch size.     

Effect of air movement on the thermal insulation of avian nests

Capsule: Air movement over a nest increases the rate of cooling within the nest cup but the walls provide good thermal insulation.

Aims: This study compared nests of six bird species of the families Fringillidae and Motacillidae to investigate the insulative properties in still and moving air treatments. It was hypothesized that differences in nest size and moving air would differ between species and would have a significant effect on insulatory values of the nests.

Methods: Nest dimensions were measured for a total of 35 nests from six species. Thermal properties of the nests were recorded using temperature loggers within nests placed in a wind tunnel under still and moving air conditions.

Results: Insulatory values and internal nest cooling rates were significantly increased by moving air. There was no significant difference between species for the thermal properties of nests but nest mass correlated with greater insulatory values and a lower rate of cooling within the nest cup. Nest wall thickness had no significant effect on the thermal characteristics of the nests.

Conclusion: The use of a constructed nest mitigated the effects of air movement but the differences between species reflected difference in nest mass rather than wall thickness.     

Comparative nest survival of three sympatric loon species breeding in the Arctic

Identifying factors influencing nest survival among sympatric species is important for understanding and managing sources of variation in population dynamics of individual species. Three species of loons nest sympatrically in northern Alaska and differ in body size, life history characteristics, and population trends. We tested the effects of competition, nest site selection, and water level variations on nest survival of Pacific Gavia pacifica, yellow‐billed G. adamsii, and red‐throated loons G. stellata on the Arctic Coastal Plain in Alaska. Although overall nest survival rates did not differ between species, the factors influencing nest survival varied. Nest site selection influenced nest survival for Pacific and yellow‐billed loons, with both species having high nest survival when nesting on islands and peninsulas, likely due to a reduction in access by terrestrial predators. However, on mainland shorelines, Pacific loons had lower nest survival than yellow‐billed loons, and used a higher proportion of vegetation mats for nest sites suggesting that their smaller body size makes them less adept at nest defense. Nest site selection did not influence nest survival of red‐throated loons corresponding to our result of no nest site preferences by this species. Initiation date had a strong influence on nest survival for Pacific and yellow‐billed loons with nests laid earlier having higher survival. Pacific and yellow‐billed loon nests were susceptible to flooding due to precipitation, which contrasted with red‐throated loons that nest on smaller lakes with lower water level variations. Competition did not affect nest survival for any of the species likely due to most territorial encounters occurring prior to incubation. The only influence we found on red‐throated loon nest survival was differences among years. Our results indicate that loons chose nest sites based on predation risk and that factors influencing breeding success of closely related species may differ under similar breeding conditions.     

Adaptive nest clustering and density‐dependent nest survival in dabbling ducks

Density‐dependent population regulation is observed in many taxa, and understanding the mechanisms that generate density dependence is especially important for the conservation of heavily‐managed species. In one such system, North American waterfowl, density dependence is often observed at continental scales, and nest predation has long been implicated as a key factor driving this pattern. However, despite extensive research on this topic, it remains unclear if and how nest density influences predation rates. Part of this confusion may have arisen because previous studies have studied density‐dependent predation at relatively large spatial and temporal scales. Because the spatial distribution of nests changes throughout the season, which potentially influences predator behavior, nest survival may vary through time at relatively small spatial scales. As such, density‐dependent nest predation might be more detectable at a spatially‐ and temporally‐refined scale and this may provide new insights into nest site selection and predator foraging behavior. Here, we used three years of data on nest survival of two species of waterfowl, mallards and gadwall, to more fully explore the relationship between local nest clustering and nest survival. Throughout the season, we found that the distribution of nests was consistently clustered at small spatial scales (?50–400 m), especially for mallard nests, and that this pattern was robust to yearly variation in nest density and the intensity of predation. We demonstrated further that local nest clustering had positive fitness consequences – nests with closer nearest neighbors were more likely to be successful, a result that is counter to the general assumption that nest predation rates increase with nest density.     

Increased nest defence of upland‐nesting ducks in response to experimentally reduced risk of nest predation

Parent birds should take greater risks defending nests that have a higher probability of success. Given high rates of mammalian nest predation, therefore, parents should risk more for nests in areas with a lower risk of mammalian predation. We tested this hypothesis using nest defence data from over 1300 nests of six species of dabbling ducks studied in an area where predation risk had been reduced through removal of mammalian predators. When predator removal reduced nest predation, the ducks increased risk taking as predicted. Also as predicted, risk taking varied inversely with body size, an index of annual survival, among species. For ducks to vary nest defence in response to variation in predation risk they must be able to assess the risk of nest predation. Because ducks modified nest defence in the breeding season immediately following predator removal, ducks may be able to assess predator abundance indirectly (e.g. by UV reflection from urine) rather than by seeing or interacting directly with the predators.     

Elevation has contrasting effects on avian and mammalian nest traits in the Andean temperate mountains

Nest building is a widespread breeding strategy across taxa. Nest composition and structure can play a critical role in the breeding success and/or adult survival of nest‐building vertebrates. Although nest traits are expected to vary adaptively across elevational gradients, few studies address this relationship. We studied the variation in nest traits (composition and structure) across elevation for two taxa with two different functions in the Andean temperate forests of southern Chile: a bird (Aphrastura spinicauda, Furnariidae, 170 breeding nests) and a marsupial mammal (Dromiciops gliroides, Microbiotheriidae, 91 winter torpor nests). For A. spinicauda, we further assessed how nest traits influenced clutch size and hatching success. Both species used fewer types of nest materials (items) with increasing elevation, and a greater proportion of leaves were used in highland compared to lowland forests. Aphrastura spinicauda used feathers and hair, and D. gliroides used bryophytes more frequently in lowland forests. The mass and volume of nests decreased with increasing elevation for A. spinicauda and increased for D. gliroides. Nest traits had subsequent fitness consequences for A. spinicauda, such that: (i) greater cup volume and depth were associated with larger clutch sizes, (ii) more items used during nest building were linked to improved clutch size at high elevation only, and (iii) nest wall thickness was negatively associated with hatching success. Thus, in temperate mountain ecosystems, elevation may be an important factor influencing nest‐building behaviour for cavity‐using vertebrates. However, the direction of the elevational effects may vary among taxa and nest functions in these ecosystems.     

Artificial nest predation rates vary among habitats in the Australian monsoon tropics

Rates of nest predation have frequently been shown to differ between fragmented and unfragmented habitats, but have rarely been compared among natural habitats in the same geographic region. In this study, artificial nests of two types (open cup and domed) were placed in four habitats (mangroves, monsoon rainforests, eucalypt woodlands and paperbark swamps) over 12 months in three localities near Darwin in the Australian monsoon tropics to determine the effects of habitat, season and nest type on the rate of nest predation. A quail egg and a similarly coloured plasticine egg were placed in each nest. Habitat had a strong effect on nest predation rates, with nests in mangroves experiencing predation rates more than four times higher than those in eucalypt woodlands and paperbark swamps. Despite the strong rainfall seasonality of the region, there was no consistent seasonal variation in nest predation rates. Nest type also had little influence on predation rates, except in paperbark swamps where open cup nests suffered a higher predation rate than domed nests. The study indicates that generalised nest predation rates for tropical regions, even for small areas (e.g. <17 km radius), might overlook substantial variation between habitats. Such variation confounds purported differences in nest predation rates between tropical and temperate regions.     

Conformity to Bergmann's rule in birds depends on nest design and migration

Ecogeographical rules attempt to explain large‐scale spatial patterns in biological traits. One of the most enduring examples is Bergmann''s rule, which states that species should be larger in colder climates due to the thermoregulatory advantages of larger body size. Support for Bergmann''s rule, however, is not consistent across taxonomic groups, raising questions about what factors may moderate its effect. Behavior may play a crucial, yet so far underexplored, role in mediating the extent to which species are subject to environmental selection pressures in colder climates. Here, we tested the hypothesis that nest design and migration influence conformity to Bergmann''s rule in a phylogenetic comparative analysis of the birds of the Western Palearctic, a group encompassing dramatic variation in both climate and body mass. We predicted that migratory species and those with more protected nest designs would conform less to the rule than sedentary species and those with more exposed nests. We find that sedentary, but not short‐ or long‐distance migrating, species are larger in colder climates. Among sedentary species, conformity to Bergmann''s rule depends, further, on nest design: Species with open nests, in which parents and offspring are most exposed to adverse climatic conditions during breeding, conform most strongly to the rule. Our findings suggest that enclosed nests and migration enable small birds to breed in colder environments than their body size would otherwise allow. Therefore, we conclude that behavior can substantially modify species’ responses to environmental selection pressures.     

Experiments on clutch size and nest size in passerine birds

Summary Results of experiments on three passerine species suggest that brood size may be constrained by nest size, since the breeding success of pairs provided with large nestcups was greater than that of those provided with small artificial nestcups. These results may have important implications, e.g. to the design of experiments involving manipulation of clutch and brood size. A small nestcup is requisite for successful hatching during the incubation period, but a large one for successful rearing during the nestling period. In nature this difference may select for types of nesting materials that are elastic, such as mosses and lichens. However, experiments showed that such materials rapidly absorb rainwater but only slowly dry out. In addition, because large nests dry out more slowly than small nests, selection will favour small nests among those open-nesting species that have exposed nests. A further possible nest size constraint on open-nesters is nest predation. However, no difference in the predation rate was found in experiments with small and large artificial nests.     

Aggressive neighbors and dense nesting: nest site choice and success in high-Arctic common eiders

Minimizing the risk of nest predation has led some bird species to exploit the nest defense behavior of other species. At Nasaruvaalik Island, Nunavut, Canada, some common eiders (Somateria mollissima borealis) nest within the boundaries of Arctic tern (Sterna paradisaea) colonies, while others nest elsewhere on the island, away from the terns. We tested the effects of location (within vs. outside the tern colonies), density of common eider nests, and annual variation on the nesting parameters of common eiders. Our results suggest that nesting in association with Arctic terns does not confer an obvious benefit to eiders. Such associative nesting of eiders and terns may be the result of overlapping habitat preferences between the two species, or a general scarcity of suitable nesting habitat for ground-nesting species in the high Arctic. However, eiders nesting in higher densities with other eiders had greater nest success and lower total clutch predation, indicating a positive correlation between nest density and success.