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Attendants at Tree Swallow Nests. II. The Exploratory-Dispersal Hypothesis

Michael P. Lombardo
The Condor
Vol. 89, No. 1 (Feb., 1987), pp. 138-149
DOI: 10.2307/1368768
Stable URL: http://www.jstor.org/stable/1368768
Page Count: 12
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Attendants at Tree Swallow Nests. II. The Exploratory-Dispersal Hypothesis
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Abstract

Attendants (i.e., conspecific individuals exclusive of the breeding pair) are common visitors at active Tree Swallow (Tachycineta bicolor) nests during the nestling period. An examination of the chronology of attendant behavior revealed that attendants (i) visited several boxes, (ii) were especially attracted to preferred breeding locations, (iii) significantly increased in number as the breeding season progressed, (iv) were mostly young of the year by the end of the breeding season, and (v) chased nestlings as they fledged. Members of large, premigratory flocks of Tree Swallows examined nest boxes during late August. Attendants were not helpers at the nest and had no demonstrable effect on parental reproductive success (Lombardo 1986a). Tree Swallows, because they are nonexcavating cavity nesters, face intense competition for a limited number of suitable nest sites. Sexually mature attendants at nests during the egg laying, incubation, and early nestling periods may be searching for exploitable breeding opportunities (e.g., see Leffelaar and Robertson 1985, Stutchbury and Robertson 1985). I hypothesize that hatching-year attendants, common during the late nestling period, are individuals in search of potential future nest sites. I call this the "exploratory-dispersal" hypothesis. Exploratory dispersal should be of special selective advantage to migratory, nonexcavating cavity nesters.

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