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Bird nests represent an extended phenotype that is variable among and within species in terms of nest location and construction materials. It has also been suggested that nests indicate niche construction, although empirical evidence to support this is lacking. The nest wall is often considered to confer some insulation because this would help minimize the energetic expenditure by the incubating adult. However, it has been previously suggested that nests are constructed primarily for their structural role rather than for insulation, but to date, studies have used a variety of techniques to investigate the insulation of nest walls but only for relatively few species. This study used temperature loggers to determine insulatory values of nests for 16 previously undescribed species and to replicate values for eight previously described species. In addition, data for nest wall insulation that were determined using temperature loggers have been collated for a total of 32 different passerine species. The effects of nest dimensions, mass, and composition on these values were examined. Base thickness, but not wall thickness, and nest mass significantly positively affected insulatory values. This study found that the proportions of feathers and moss in the nest wall significantly positively correlated with insulatory values. This suggests that there is a key role for nest materials in determining insulation, which provides empirical evidence that nest building constitutes niche construction. The data will also help us interpret data from future studies of the thermal properties of nests. Ultimately, we need to develop our understanding of the role of insulatory values in the evolution of nest function. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]