Abstract

Animals that use materials to build nest structures have long since fascinated biologists and engineers alike. Avian nests are generally composed of collected materials brought together into a cup-like structure in which the bird sits to incubate eggs and, in many cases, it is where chicks are reared. Hence, the materials in a nest can be presumed to be loaded in compression, but relatively few studies have investigated the mechanical role of the nest elements and their position within the structure. However, recent studies on avian and primate nests have used engineering tests to quantify the structural properties of the nest elements to provide insight into how animals arrange the materials they collect and their mechanical role within the nest. In two studies, we deconstructed nests from Common Blackbirds (Turdus merula) and Bullfinches (Pyrrhula pyrrhula) into their component parts. We then used three-point bending tests to investigate regional variation in the structural properties of these elements within the nest. Results indicate that the birds use materials with different physical characteristics in various parts of the nest, thereby providing an indirect indication of nest-building behaviour in these species. We also used a novel cutting test, previously developed to measure the mechanical anisotropy of keratin, to investigate the mechanical behaviour of the mud-cup structure found in Common Blackbird and Song Thrush (Turdus philomelos) nests. This allowed us to determine whether these species utilise and arrange mineralised materials in a particular way to improve the toughness of their nests. The applicability of similar and other mechanical testing methods are discussed in relation to future investigations of the architecture and function of songbird nests.