The results suggest that occasional food shortages play a crucial role in the ecology and evolution of island populations, and that this might be undetected in short-term studies.This species was formerly placed in the genus Amazilia. tobaci used a wide variety of artificial flowers, and a wide range of flower densities in field manipulations, than did conspecifics from Trinidad. Among hummingbirds in general, low wing disc loading indicates a capacity to forage at a wide variety of flowers, which suggests that the Tobago population has undergone "within-phenotype nich expansion." Two experiments showed that individuals from the Tobago population of A. tobaci had longer wings than Trinidad conspecifics, resulting in lower wing disc loadings (ratio of body mass to area swept out by the wings). We found no increase on Tobago in the intrapopulation variance of any morphological parameter important to feeding. Ecological differences between the two populations during the food shortage may be linked to a phenotypic difference. Median values for niche breadth, population density, and population density per unit resource were not significantly greater on Tobago than on Trinidad. tobaci relative to food, narrowing when food was abundant. At both sites, niche (diet) breadth responded in density-dependent fashion to changes in food density, broadening with high densities of A. These effects of "ecological release" on Tobago were apparent for only 3 mo, however, and when data for an entire year are compared there were few statistically significant contrasts between Tobago and Trinidad populations. tobaci primarily used flowers that matched their bill size, which resulted in narrower feeding niche than on Tobago. On Trinidad, where many flowers were visited by the other hummingbird species, A. tobaci utilized variously sized and shaped flowers of numerous plant species. The Trinidad population endured the food shortage along with six other hummingbird species. tobaci faced only two other, uncommon species of nectar-feeding birds, which had very different feeding habits. From September through November, nectar was scarce at both sites. tobaci population faced a severe food shortage. At both sites, food available to nectar-feeding birds varied > 100 fold over the year. The two sites had nearly identical climates, and similar assemblages of flowers visited by hummingbirds. Arima Valley of northern Trinidad and in central Tobago. We monitored populations of Amazilia tobaci for 13 mo at study sites in the. tobaci on Tobago would have a broader feeding niche and a denser population than would A. Trinidad has 15 other hummingbird species, Tobago only 4 others. Resident populations of the Coppery-rumped Hummingbird, Amazilia tobaci, occupy the West Indian Islands of Trinidad and Tobago. The perches selected are typically on trees, close to the flowers visited, and in a low vertical and middle horizontal position, surrounded by low foliage density, probably to minimize heat loss. The large amount of time spent on the perches makes them an important element of the habitat. Flower use is not directly related to flower abundance (chi(2)9, = 1,546, p<0.0001), with Justicia brandegeana and red-flowered Salvia splendens being selected and Impatiens balsamina being rejected. Territorial defence accounted for 2% of total time, mostly against Coereba flaveola, an introduced nectarivorous species that seem to be an important competitor of A. 80%) and only 15.5% for foraging, devoted essentially to flower visitation and only 0.3% for hunting and drinking water. amazilia spent an important part of its time resting on perches (ca. This study deals with the time-activity budgets of Amazilia amazilia, a territorial hummingbird, and its preferences for different flower species and perches in the gardens of Lima (Peru) in September 2001.
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