Multiple-factor influences upon feeding flight rates at wading bird colonies (Alias: Are flight-line counts useful?)

Abstract

The temporal patterns of feeding, resting, and reproductive behavior in colonial wading birds have been studied by a number of investigators (Recher and Recher 1972, King 1974, Capen 1978, Custer and Osborn 1978, Kushlan 1978) both on a short-term (daily) and long-term (annual) basis. In coastal marine environments, activities at colonies are influenced by tides (Recher and Recher 1972, Krebs 1974, Custer and Osborn 1978), time of day (Kushlan 1978) and phase of the nesting cycle (Kahl 1964). The purpose of this paper is twofold: (1) to examine the effects of tide, time of day (physical factors), nesting phase, colony site, and spe cies identity (biological factors) on feeding flight rates at breeding col onies and, as a result of this, (2) to evaluate the usefulness of feeding flight counts as an index of the number of nests in the colony. Earlier work suggests that the relationship between the number of in dividuals flying to and from the nesting colony may be quite consistent with nest numbers. Thus, by monitoring flights from remote locations, ob servers might obtain relatively accurate census data while minimizing time and disturbance at colonies. Recent concern for the deleterious impact of humans at waterbird colonies (Buckley and Buckley 1976, Ellison and Cleary 1978) underscores the need to investigate alternative census methods.