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Bird nests can be complex bio-engineered structures constructed from a range of materials to provide a site for incubation, and in many species chick rearing. Reports of the materials used in nest walls and cup linings are typically qualitative and do not assist in understanding the functional properties of the structure as a whole. This paper provides size and composition data for nests from four species of the Motacillidae family: the meadow pipit (Anthus pratensis), pied wagtail (Motacilla alba), grey wagtail (Motacilla cinerea), and the yellow wagtail (Motacilla flava), three species of the Sylviidae family: willow warbler (Phylloscopus trochilus), Eurasian reed warbler (Acrocephalus scirpaceus) and Eurasian blackcap (Sylvia atricapilla), and the dunnock (Prunella modularis) of the Prunellidae family. Three hypotheses were tested: do nest dimensions correlate with body mass? Is it possible to distinguish among species based on their nest composition; and for individual species? Is it possible to distinguish between the cup lining and outer nest wall based on the materials used in construction? Nest composition and size varied among species although the degree of intra-specific variation was different. Size of a nest was unrelated to average female adult body mass. Composition relied on similar types of materials but in differing quantities between species. It was possible to distinguish among species in terms of nest construction, and between the cup lining and the outer nest, on the basis of at least one of the component materials. By providing quantitative data on composition, it may be possible in the future to understand better the structural, insulative and hydrological properties of the nest. Such information will be invaluable as we begin to develop an understanding of the factors that have driven evolution of nest architecture.

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’ nests exhibit a considerable amount of plasticity in their size and construction. Indeed, several studies have shown that geographical location can affect this plasticity because local climatic conditions appear to affect nest-construction behaviours. This study examined nests collected in the UK and housed either at the University of Lincoln or at the British National Nest Reference Collection at the Hunterian Museum, University of Glasgow. Our aim was to increase the species diversity and the sample sizes for each species, over and above published studies. Mass and linear dimensions were recorded from nests of five finch species and two thrush species together with longitude and latitude for the nest site locations. An effect of species was shown for all finch nest dimensions measured but only for particular thrush dimensions. Latitude (range from 50.4 to 57.8°N) had no effect on nest measurements taken for thrush or finch species. However, while longitude (range from 6.8°W to 1.1°E) had no effect on thrush nests, it had a significant effect on the nest mass of finches, with nests constructed in the west being lighter in mass than those from the east. Previous studies examining the effects of latitude have used nests collected from different locations and built in a single year, which suggests that climatic conditions will be broadly comparable between locations. We found that museum collections have nests from a range of years and this rather limits their value in studies trying to ascertain the effects of location. Across different years there may be many unknown factors contributing to the patterns observed. We suggest that any future studies of the effects of climate on nest construction will have to rely on materials especially collected rather than using museum collections.