Seasonal Patterns in Daily Flight Distance and Space Use by Great Egrets (Ardea alba)

Abstract

In an effort to quantify the value of wetland habitats, GPS technology was used to document the movement patterns of 16 Great Egrets (Ardea alba) in North America. Patterns in daily flight distances and utilization distributions (UD; estimates of area occupied on the ground) were documented throughout the annual cycle. Maximum Daily Displacement (MDD), the farthest distance occupied by a bird from colony/roost (central place) in 24 hr was greatest (4.3 ± 0.1 km) during breeding season and lowest (3.3 ± 0.1) during post-breeding season. As birds visited multiple foraging sites and made multiple round trips to central places, this Total Daily Distance (TDD) was also measured. It increased from a mean of about 12 km during the incubation phase to about 35 km at the time of fledging. Average TDD was greatest during breeding season (14.2 ± 0.3 km) and lowest during winter (11.0 ± 0.2 km). The utilization distribution increased from 128 (± 21.3) ha during breeding season to 179 (±32.6) ha during winter. Birds that foraged at tidal sites used 183.3 (± 22.2) ha, twice as much area as birds that foraged strictly in freshwater sites (89.6 ± 21.3 ha).