Conditions and Significance of Night Feeding in Shorebirds and Other Water Birds in a Tropical Lagoon

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Abstract
On a small bay of the Chacopata lagoon complex in northeastern Venezuela, we analyzed the temporal feeding activity patterns of shorebirds and other water birds, and we determined the factors or conditions related to these patterns. During daytime and night-time observations, we measured the abundance of each species as well as environmental factors (time, wind velocity, cloudiness, tide level, presence of moonlight and bioluminescence). A night vision module (light intensifier) was used during nighttime observations. Samples .times. species matrices were summarized by reciprocal averaging (RA) analysis, and the information was related to environmental factors. Feeding activity patterns were related most significantly to time of day, i.e. daytime and nighttime. Some species like "egrets," the Whimbrel (Numenius phaeopus), and the Black-bellied Plover (Pluvialis squatarola) fed principally during daylight, but most other species (including a majority of shorebird species) fed more regularly and in higher numbers at night. Lesser and Greater yellowlegs (Tringa flavipes and T. melanoleuca, respectively) and Willets (Catoptrophorus semipalmatus) foraged with comparable frequency during the day and the night. Daytime and nighttime data were analyzed separately, and tide level best explained both the variations of nocturnal and diurnal abundance of foraging birds. Nocturnal feeding may be a natural habit in response to regularly limited feeding space and time mainly induced by tide.