FACTORS AFFECTING FOOD PROVISIONING OF NESTLING BLACK-THROATED BLUE WARBLERS

Using video cameras at nests, we measured rates, quantities, and types of food delivered by male and female Black-throated Blue Warblers (De ndroica caerulescens) to nestlings of different ages and at different times of day and nesting season. Based on 89 1.5-2 h observation perio ds at 18 nests, all of which contained four young, we found that larva l Lepidoptera comprised 60-87% of the estimated prey biomass brought t o nestlings and that the female and male parents delivered approximate ly equal amounts of food over the nesting cycle. Food provisioning rat es did not vary with Lime of day or with parental age, but did increas e significantly with age of nestlings and decrease with time of season (early vs mid-summer). The lower rate and quantity of provisioning in mid-summer was reflected in significantly slower growth of nestlings in that part of the season, suggesting constraints on parental food pr ovisioning, perhaps due to lower food availability.