Use and importance of feathers as nest lining in tree swallows (Tachycineta bicolor)

Abstract

Tree Swallows (Tachycineta bicolor) commonly line their grass nests with feath- ers of other species. In one of three years studied, there was a significant negative correlation between numbers of feathers in the nest and chick nestling periods (i.e. broods surrounded by more feathers fledged earlier). In the third year of the study, the population was divided into two groups, balanced for all measurable aspects of parental quality. In the group, all feathers were removed daily and in the control group all feathers were allowed to remain. All nests and their contents were disturbed equally. Chicks in removal nests had lower growth rates (in mass, wing chord and tarsus) and higher infestations of mites and lice. I suggest that feathers aid chicks directly by preventing hypothermia and indirectly through higher growth rates by allowing earlier fledging when necessary. Protection from ectoparasites may be an important advantage in natural nests where nest cavities are not cleaned out annually. Inadvertent removal of feathers from nest boxes may be an important cause of posthatching declines in feather numbers. Received 19 July 1991, accepted 14 August 1992. TREE SWALLOWS (Tachycineta bicolor) usually line their nests with feathers, and one of the most conspicuous and distinctive behaviors during this swallow's breeding season is the frequent contests over feathers. These contests involve high-speed aerial chases accompanied by considerable aerial jostling and bodily con- tact, often involving several birds (e.g. Wey- demeyer 1934, Kuerzi 1941; for an illustration see Audubon (Peterson and Peterson 1981:plate 276)). Having been intrigued by these aerial contests and the apparent worth of the resource being contested, I began a study of the feathers used in Tree Swallow nests in 1987. I present here a brief description of the natural history of the use of feathers as nest lining, some cor- relative evidence of the feathers' importance, and the results of an experimental study doc- umenting the effect of feathers in the nest on chick growth and ectoparasite infestations. The nest linings of birds generally have been thought to provide insulation for the devel- oping offspring (e.g. Haftorn 1978, Capreol 1983, Moller 1984) or protection against ectoparasites (e.g. Wireberger 1984), and my experiment test- ed the two predictions that feather relnoval would lead to: (1) decreased chick growth and/ or survival; and (2) increased numbers of ec- toparasites. METHODS