Showing papers by "H. Lisle Gibbs published in 1985"

Preferred Nest Spacing of an Obligate Cavity-Nesting Bird, the Tree Swallow

Abstract: In order to determine the preferred dispersion of a population of breeding Tree Swallows (Tachycineta bicolor) in Ontario, we set up an abundant supply of nest boxes with a variety of distances between them. The 72 boxes were arranged in 12 equidistantly spaced spirals. Within a spiral, the distance between boxes was much smaller than between spirals. Over five breeding seasons, we observed the order and positions in which swallows settled in the spirals. Pairs of swallows usually settled in empty spirals before settling in spirals occupied by conspecifics, but they did not avoid nesting in spirals occupied by Eastern Bluebirds (Siulia sialis). Swallows did not show any spacing preferences when their nearest neighbors were in different spirals, and were therefore more than 36 m away. Within spirals, however, swallows nested as far as possible from each other when their nests were less than 14 days apart. Swallow nests in the same spiral also tended to be spaced out temporally. We conclude that, over the range of distances within a spiral, Tree Swallows prefer to space their nests as far from conspecifics as possible. The observed spacing pattern probably arises from territorial behavior that is directed toward defense of a nest site from intruders. Breeding birds disperse their nests in a variety of patterns ranging from the tightly clumped distribution of colonial species to the uniform distribution of territorial species (Lack 1968). The spatial distribution of resources such as food, nest sites, and nest materials; the intraspecific competition for these resources and for mates; and predation pressure are some of the factors determining the breeding dispersion of individuals (Crook 1965, Lack 1968, Hoogland and Sherman 1976). In this paper, we report on an experimental approach to determine the preferred nesting dispersion of a cavity-nesting species, the Tree Swallow (Tachycineta bicolor). Swallows (Hirundinidae) show varying degrees of gregariousness during the breeding season. Dispersion may depend upon a particular species’ nesting requirements. Some species build their own nests, while others use existing crevices in trees, rocks, and walls, or old burrows excavated by other animals. Those species that build their own nests have some choice in the nature of their association with conspecifics, and intraspecific interactions are probably the most important determinants of their dispersion patterns (e.g., Hoogland and Sherman 1976, Snapp 1976). For example, Cave Swallows (Hirundo @vu) and Cliff Swallows (H. pyrrhonota), which build globular nests of mud pellets, breed in dense colonies, as do Bank Swallows (Riparia riparia; Bent 1942) and White-backed Swallows (Cheramoeca leucosternum), which excavate their own burrows in sand banks (Serventy and Whittell 1976). On the other hand, another burrower, the Banded Sand Martin (Riparia cincta), nests solitarily (McLachlan and Liversidge 1965) and another mud-nest builder, the Barn Swallow (Hit-undo rustica), nests solitarily or in loose colonies (Snapp 1976). Those species that must nest in existing holes and cavities have distributions that are determined primarily by the availability of suitable nest sites (von Haartman 1957, Holroyd 1975). The Tree Swallow, Purple Martin (Progne subis ), and Northern Rough-winged Swallow (Stelgidopteryx serripennis) are examples of obligate cavity-nesting swallows. Cavity-nesting species show considerable intraspecific variation in their nesting behavior, and may nest either solitarily or colonially, depending on the distribution of nest sites (Bent 1942). Since spacing patterns are so diverse in cavitynesters, it is of interest to determine which, if any, nesting dispersion pattern is actually preferred. Nest spacing preferences of cavity-nesting species can be determined by providing many nest sites with different distances between them. Once the preferred spacing is known, one can begin to look for the behavioral mechanisms by which the spacing pattern is achieved, and for any effects of the spacing pattern on fitness.