Nest building as a missing piece in biparental care.

Many birds practise biparental care, providing useful systems to study its evolution. Although nest building has largely been ignored as biparental behaviour, parental conflict and cooperation could begin during nest building, before incubation and offspring provisioning. While there are ample data on biparental incubation and provisioning in model species like zebra finches (Taeniopygia guttata), nest-building data largely concern material collection and preference in the males, not building by the females. Here, we collected data on building by both female and male zebra finches to test whether building behaviour depends on the behaviour of their mate or on the material they used to build their nest. Males held nest material more frequently when their female was in the nest, while females held nest material longer when their male was away from the nest. But neither females nor males altered their building behaviour in response to changes in their partner holding nest material. Males that built with stiff material held the material more frequently than those that built with flexible material, while females manipulated stiff and flexible materials similarly. The next step will be to determine whether these building interactions affect later stages of parental care in the wild or in other species.