COMPETITION, RESOURCE USE AND HABITAT SELECTION IN 2 INTRODUCED HAWAIIAN MANNIKINS

We analyzed patterns in geographic distribution and resource use for t wo species of introduced mannikins (Aves: Estrildidae) in four urban p arks across southern Oahu, Hawaii. Both species fed exclusively on gra ss seeds. Resource levels (i.e., the density of grass stems) cycled co ntinously in the parks due to alternating management practices (i.e., watering and mowing). Both species were common in urban parks during s ummer months but not during winter. During summer, both species increa sed significantly as resource levels increased. Nutmeg Mannikins (Lonc hura punctulata) occurred in all parks but were rare in those parks wh ere Chestnut Mannikins (Lonchura malacca) were common. This was true e ven when resource levels between parks did not differ significantly. W e interpreted this as evidence for competition between these species. We also tested two specific predictions of the shared-preference model of density-dependent habitat selection. According to this model both species should occur together in a park only when the density of grass seeds in that park is high. A second prediction of the model is that at low resource levels only one species (i.e., the behaviorally domina nt species) should occur. Both of these predictions failed. We observe d both species together in parks only rarely, and in some cases of coe xistence resource levels were quite low. Each species was seen by itse lf in at least one park.