Variation in the Costs, Benefits, and Frequency of Nest Reuse by Barn Swallows (Hirundo rustica)

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Abstract
The frequency of nest reuse and the costs and benefits of this behavior were investigated in a population of Barn Swallows (Hirundo rustica) at Delta Marsh, Manitoba, during 1984-1986. Slightly less than half the clutches were laid in old nests, and this proportion did not change seasonally except in one late year when old nests were preferred by late-nesting pairs. The delay between nest and clutch initiation was greater for new vs. old nests, but only significantly so in June and July. Parasites (hematophagous mites) were common in old nests that had been used the previous year and significantly reduced chick survival. Swallows appeared to be able to assess parasite load and selected unparasitized old nests for the first nesting attempt. Nest instability did not appear to be a cost of nest reuse. The mean reproductive success per pair was equal for swallows using old vs. new nests, suggesting that birds can assess the costs and benefits of particular nests and nest sites. Nest reuse was, however, considerably less frequent than in other studies, presumably because the costs and benefits of this behavior vary geographically. In particular, the breeding season at Delta Marsh is extended, and the time delay caused by building a new nest is therefore less important than elsewhere. More birds have the option of avoiding the parasite costs of nest reuse while still successfully rearing two broods. Thus, individuals apparently maximize their reproductive success by adjusting their nesting strategy to account for the local costs and benefits of the two nesting options.