Black Skimmers Feed When Light Levels are Low

Abstract

Abstract. Previous studies documented that Black Skimmers, Rynchops niger; tend to forage at night but did not examine which environmental variables explain nocturnal foraging. Foraging frequency and environmental variables were studied at a large breeding colony of skimmers on an urbanized barrier island on the west coast of Florida, USA. To determine which variables influenced foraging, the number of skimmers departing to forage was counted for 120, one-hour periods through the day and night from 30 May–29 August, 2007. Using generalized linear models, factors were most associated with skimmers departing to forage were identified. These models included: light level, temperature, wind, wind direction, relative humidity, tide height, tide stage (incoming, outgoing, or slack) and status of the colony (mostly eggs, chicks, or fledglings). Light level was the only factor to significantly influence the amount of foraging (Wald = 9.40, d.f. = 1, p = 0.002). The relationship was negative, as light levels decrea...