Population size reductions are usually expected to result in decreases of within-population genetic variation. We here report on allozyme variation in (1) the endemic population of the Laysan finch (Telespiza cantans) that was reduced by a major population crash during the early 1900s and (2) translocated populations on three islets of a distant atoll (Pearl & Hermes Reef). These populations resulted from the introduction of 108 birds to one islet in 1967 and subsequent dispersal to the other islets. Variation in 33 allozyme loci on Laysan was found to be lower than the average in avian populations, matching theoretical expectation. Unexpectedly, the average heterozygosity of Pearl & Hermes populations is higher than at Laysan, and significantly so for two of five polymorphic loci. Variation in allele frequencies is relatively high for avian populations (FST= 0.049), both among the islets of P& H, and between P& H and Laysan. This suggests that isolation within the tiny, translocated populations has resulted in a significant level of genetic differentiation during a relatively short time period (less than 20 years).

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. Onethird 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 ofbreeding 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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The typical Iaysan Finch (Telespiza cantans) nest on Iaysan Island is composed primarily of the bunchgrass Eragrostis variabilis, and is hidden from view within a bunchgrass clump. About one-third of the nests have two or more plants species in the nest substrate and canopy. Nests are usually in the lower two-thirds of the bunchgrass clump, and in the lee of the prevailing winds. The dimensions of nests and nest substrates were compared between the predominant vegetation associations: bunchgrass and viney. Almost all nests occurred in these two associations. Nests in the bunchgrass association had more of their canopies composed of a single plant species, had substrates with greater maximum heights, had more cover over the nest cups, and had wider outer nest diameters. Nine other nest and nest substrate variables showed no difference between the two vegetation types, nor did clutch size and fledging success differ significantly, although evidence suggested that fledging success may differ for early (or late) season nesters.Nearest-neighbor distances of simultaneously active nests were larger in the bunchgrass association than in the viney, and nest densities were approximately half. Nests were relatively more aggregated in the viney association. The viney association occupies half as much total area as the bunchgrass association, but it appears to be the most productive per unit area for nesting. The rapid invasion over the past 29 years by a non-native bush (Pluchea indica) into this important vegetation association warrants further study into the possibility of vegetation control. Clapp 1973, Sincock and Kridler 1977). Otherwise, their nesting habits have been little studied. The location, spacing, and composition of avian nests profoundly affect the microclimate in which the egg develops (Drent 1983) as well as the egg' s subsequent success (Rendell and Robertson 1989). Numerous factors influence nest characteristics and site choice, e.g. prevailing winds (Ferguson and Siegfried 1989) the density of vegetation (Leonard and Picman 1987), the distribution of available nest sites (Hagan and Walters 1990, Kerpez and Smith 1990), and intra-and interspecific competition (Rendell and Robertson 1989). Many recent studies have attempted to summarize specific habitat attributes that are correlated with nest sites selected by various species (Burger and Gochfeld 1988, Mc-Auliffe and Hendricks 1988, McCallum and Gehlbach 1988, Rendell and Robertson 1989). My objectives were to describe the nest characteristics, nest spacing, and relative reproductive success for Laysan Finch nests in the two major vegetation associations on Laysan Island, so that nest site selection could be better understood for this species. Laysan was severely affected by humans in the [3441