Population Size and Natural History of Mariana Fruit Bats (Chiroptera: Pteropodidae) on Sarigan, Mariana Islands

摘要

Based on count results, we estimated the population of Mariana fruitbats (Pteropus mariannus Desmarest) on Sarigan, Mariana Islands, to number150-200 bats in 1999, 185-235 bats in 2000, and about 300-400 bats in 2001.Our results, plus those of two previous surveys, indicate that bat abundance onthe island probably remained relatively stable at about 125-235 animals duringmuch of the period from 1983 to 2000, then increased suddenly in 2001, mostlikely due to immigration from a neighboring island. Sarigan's population differsfrom those of larger islands in the archipelago by usually having smaller roostsizes, typically 3-75 bats, and large numbers of solitary bats that at times compriseup to half of the population. Colonies and smaller aggregations werecomposed primarily of harems with multiple females, whereas a nearly equal sexratio occurred among solitary animals. Colonies roosted in isolated coconuttrees in open grasslands and in native forest stands of various sizes, but avoideddense coconut forest. An estimated 30-50% of harem and solitary females possessedyoung in July 1999. Bats were recorded feeding on just six species ofplants, which partly reflects the island's impoverished flora. We speculate thatfruit bat abundance on Sarigan is limited primarily by food availability ratherthan hunting losses, in contrast to some other islands in the Marianas. Our studysupports the contention that populations of P. mariannus in the northern Marianasare usually sedentary, but that interisland movements of larger numbersof bats may occur rarely.