Causes and consequences of material variation in avian nest building

Houses around the world are built with a variety of materials like timber
and brick, depending on a number of factors such as local climate and
material availability. Similarly, non-human animals such as birds use
diverse materials to build nests. Very little is known about how animals
choose nest materials, and how these choices, in turn, affect the function
of the nests they build. As an initial attempt to address this question,
we investigated the causes and consequences of nest-material use by
Dartford warblers (Sylvia undata). The warblers breeding in England show
considerable variation in nest materials: some nests are made almost
entirely of heather, while others contain a lot of grass. We found that
the warblers’ use of nest materials were explained by the composition of
the local habitats, but no evidence for relationships between
nest-material composition and insulation capacity or the breeding
performance. Warblers appear to be able to build equally functional nests
using whatever materials are readily available in respective habitats.
Studying nest-building behaviour of individual species like Dartford
warblers could inform how the use of diverse material in animal
architecture evolved.