A Telemetry-Based Study of Great Egret (<i>Ardea alba</i>) Nest-Attendance Patterns, Food-Provisioning Rates, and Foraging Activity in Kansas, USA

Abstract

The breeding season is a demanding period in an individual's annual cycle because it must balance energy gains with the competing demands of reproduction and self-maintenance and properly allocate time and energy to both. To better understand how this balance is reached, nest-attendance patterns, food-provisioning rates, and foraging patterns were studied in radio-tagged Great Egrets (Ardea alba) breeding in a mixed-species colony in Wichita, Kansas, from May–August 2010–2013. A total 900 bird-days for 16 Great Egrets (60 ± 32 days/bird) provided 777 records of feeding sites, yielding travel times, flight velocities, and flight distances. Prey-capture rates, capture efficiencies, prey sizes and aggressive interactions were recorded at rivers, ponds, and weirs. A data logger placed in the colony from 2011–2013 recorded 3,390 arrivals and departures by 14 Great Egrets, documenting nest-attendance patterns. Provisioning intervals (196 ± 18 min [SD]; Range = 30–2,044 min) differed among radio-tagged individuals and among the three years. Round-trip distances to feeding sites in 2011 (16.3 ± 17.8 km) and 2012 (16.0 ± 7.0 km) were both were longer than in 2013 (11.1 ± 3.3 km). Flight distances to feeding sites also differed among individuals and increased with breeding stage. Strike rates (strikes/min) and capture rates (prey/min) differed by year but not by microhabitat. However, capture efficiency (successful strikes/total strikes) differed among microhabitats. Fish captured at weirs averaged six times heavier than those caught at rivers or ponds, but Great Egrets also encountered rates of aggression at weirs five to 10 times higher than at the other sites. A summary of energy gains and expenditures by radio-tagged Great Egrets is described, and differences among individual birds, among years, and across microhabitats is discussed.