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The Breeding Biology of an Endangered Hawaiian Honeycreeper, the Laysan Finch

Marie P. Morin
The Condor
Vol. 94, No. 3 (Aug., 1992), pp. 646-667
DOI: 10.2307/1369250
Stable URL: http://www.jstor.org/stable/1369250
Page Count: 22
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The Breeding Biology of an Endangered Hawaiian Honeycreeper, the Laysan Finch
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Abstract

From 1986 to 1988 the breeding biology of an endangered Hawaiian honeycreeper, the Laysan Finch (Telespiza cantans), was studied on the coral island of Laysan in the Hawaiian Archipelago. Laysan Finches are apparently monogamous. Pairs defend mates and nest sites, but not feeding territories. Only the female constructs the nest and incubates. The breeding season is prolonged, but there is yearly variation in onset. Pairs can have more than one clutch per year. The average clutch size was 3.19 eggs. The modal incubation period was 16 days. One-third of all eggs laid disappeared, probably due primarily to intraspecific predation. Eggs hatched asynchronously in the order laid. Chicks fledged at 22-26 days of age, and were dependent for at least three additional weeks. Weather affected reproductive success. A severe storm in 1986 caused almost total mortality of eggs and chicks, regardless of clutch size. Later in that same year, fledglings per nest increased as clutch size increased. During the dry 1987 field season, the onset of breeding was delayed, mean egg weight decreased, the number of malformed eggs increased, and clutches tended to be smaller. Although in good years four-egg clutches produced more fledglings per nest than smaller clutches, in poorer years three-egg clutches produced at least as many or more fledglings per nest than larger clutches. In this fluctuating environment, a modal clutch size of three apparently has been selected for, possibly because it yields the highest average number of offspring per nest during both good and poor years.

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