Morphology and biomechanics of the nests of the Common BlackbirdTurdus merula

Abstract

Capsule Common blackbirds select different materials, with varying biomechanical properties, to construct different parts of their nest. Aims This study tested the hypothesis that outer components of a nest have a more structural role and so are stronger than materials used to line the cup. Methods Blackbird nests were measured prior to being dismantled to isolate structural components which were tested for mechanical strength and rigidity. Results Outer nest wall materials were significantly thicker, stronger and more rigid than materials in the inner structural wall or the cup lining. In the vertical plane materials used in the structural wall did not differ. By contrast, lining materials from the bottom of the nest cup were significantly thicker, stronger and more rigid than materials from the top of the cup. Conclusion Blackbirds use different materials in nest construction roles suited to their properties and so may be able to recognize the structural properties of these materials. Materials on the outside of the nest may have a key structural role during construction.

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

“…Common House Martins Delichon urbicum have been shown to enhance the mechanical behaviour of mudbased nesting materials, particularly in compression, with the addition of polysaccharide/sugars obtained from abundant plant fruits (Silva et al 2010). In the nests of Common Blackbirds Turdus merula plant-derived materials in the outer nest were found to be thicker, stronger and more rigid compared to the materials present within the structural wall and the cup lining (Biddle et al 2015). A similar pattern was observed in the mechanical properties of materials used in the various parts of the nests of Eurasian Bullfinch Pyrrhula pyrrhula (hereafter 'Bullfinch') (Biddle et al 2017).…”

“…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. It is also not known whether the species studied to date are representative of other species of similar size.…”

“…Whilst the nest itself is primarily where eggs are incubated (Deeming 2016) it is suggested that they have a range of other roles associated with reproduction, and perhaps even lifetime fitness (Moreno 2012;Mainwaring et al 2014a). Birds select materials during nest construction for a variety of reasons (Deeming and Mainwaring 2015), including sexual signalling (Dubiec et al 2013;Tomás et al 2013), defence from parasites or pathogens (Dubiec et al 2013), camouflage (Kull 1977;Bailey et al 2015), insulation (Hilton et al 2004;Dhandhukia and Patel 2012;Mainwaring et al 2014b) or for their structural role (Bailey et al 2014;Biddle et al 2015Biddle et al , 2017. Whether these materials are deliberately selected for specific roles has yet to be fully investigated, but it is known that variation in a particular type of material reflects its availability within the local environment (Moreno et al 2008;Surgey et al 2012;Álvarez et al 2013;Cantarero et al 2015;Briggs and Deeming 2016).…”

Nest Insulation in the European Robin (Erithacus Rubecula): Effects of Latitude and Construction Materials

“…Deeming and Biddle (2015) showed that vacuum-packing nests to remove air trapped within the walls significantly reduced the insulatory values of the nests but by only about 20% on average for four different species. Biddle et al (2015) showed that air gaps may be an important part of Bullfinch nests because they may allow convection currents through the walls. In Robin nests the presence of leaves may have trapped air, which acted in part as nest insulation but whether this idea is correct requires further investigation.…”

“…This interest has considered the various roles of nests (Moreno, 2012;Mainwaring et al, 2014a;Deeming and Mainwaring 2015) as well as quantitative analysis of materials used in construction, which can be used to distinguish nests between species (Britt and Deeming, 2011;Crossman et al, 2011;Biddle et al, 2015Biddle et al, , 2016. Moreover, there are significant relationships between environmental conditions and nest composition with individuals of species nesting in colder, high latitude environments building better insulated nests (Crossman et al, 2011;Britt and This study investigated the materials used in nests of the European Robin (Erithacus rubecula) with particular reference to their role in determining the insulation afforded by the wall structure.…”