Composition of Bird Nests is a Species-Specific Characteristic

Abstract

Bird nests represent an extended phenotype of individuals expressed during reproduction and so exhibit variability in composition, structure and function. Descriptions of nests based on qualitative observations suggest that there is interspecific variation in size and composition but there are very few species in which this has been confirmed. For these species, data of the amounts of different materials indicate that nest construction behaviour is plastic and affected by a variety of factors, such as prevailing temperature, geographic location, and availability of materials. The lack of data on nest composition is hampering our understanding of how nests achieve their various functions and how different species solve the problem of building a nest that will accommodate incubation and allow successful hatching of eggs. This study deconstructed nests of four species of the Turdidae, four species of the Muscicapidae, and six species of the Fringillidae and quantified the size of the nests and their composition. These data were used to test: 1) whether nest size correlated with adult bird mass; 2) whether it was possible to distinguish between species on the basis of their nest composition; and 3) whether, within a species, it was possible to distinguish between the cup lining and the rest of the nest based on composition. Most but not all nest dimensions correlated with bird mass. Principal component analysis revealed species differences based on nest composition and discriminant analysis could distinguish cup lining from the outer nest based on material composition. Intraspecific variation in composition varied among species and in general fewer types of material were found in the cup lining than the outer nest. These data provide insight into how nests are constructed by the different species and in conjunction with studies of the mechanical, thermal and hydrological properties of a nest, will begin to reveal how and why individual species select particular combinations of materials to build a nest.

Birds use structural properties when selecting materials for different parts of their nests

“…All thrushes construct a cup from mud mixed with plant materials except for the Song Thrush that uses wood pulp to build the cup (Biddle et al 2018). Hereafter, we refer to the 'mud cup' but whilst doing so bear in mind this difference.…”

“…Hereafter, we refer to the 'mud cup' but whilst doing so bear in mind this difference. The base of the outer nest was considered to comprise those materials found below the bottom of the mud cup, whereas the top of the outer nest was considered to comprise those materials found alongside the mud cup (Biddle et al 2017(Biddle et al , 2018. Each region of the nest was then carefully separated into its construction elements and these were then arranged in order of diameter within each region.…”

“…Nests of known provenance were collected after the breeding season was completed and were shipped to the University of Lincoln from a variety of locations across the UK. In Lincoln the nests were frozen at − 20 °C to kill biting invertebrates (Britt and Deeming 2011) before being air-dried and stored in plastic bags in cardboard boxes at room temperature (Biddle et al 2017(Biddle et al , 2018.…”

“…Nests were first deconstructed into their component parts (see Biddle et al 2018) and separated into four distinct regions: the top and base of the outer nest, the internal 'mud' cup (thrushes), and the cup lining. All thrushes construct a cup from mud mixed with plant materials except for the Song Thrush that uses wood pulp to build the cup (Biddle et al 2018).…”

“…To date, detailed descriptions of the types of materials used in nest construction are limited to only a few bird species (Deeming and Mainwaring 2015;Biddle et al 2018) and the structural properties of these are largely unknown. Studies of the structural properties of nest materials are rare (Silva et al 2010;Biddle et al 2015Biddle et al , 2017Bailey et al 2016), so little is known about whether birds are generally selective of nest materials based on their biomechanical properties.…”