FORAGING STRATEGIES AND ENERGETIC COSTS OF FORAGING FLIGHTS BY BREEDING WOOD STORKS

Wood Storks (Mycteria americana) were followed (n = 269) from their colony in east-central Georgia to foraging sites to examine the foraging travel strategies of these birds. Most sites were relatively close to the colony (median distance = 8.8 km) requiring short travel times (median time = 22.52 min). Directness ratios (total distance flown/direct distance) for 89 mapped foraging flights suggested that storks hew relatively straight paths to feeding areas. Comparison of flight (air) speeds determined from this data with speeds determined from energetics models suggested that storks minimized flight energy costs rather that maximized range during foraging travel. Estimated energetic costs of flapping and soaring modes of flight were 204.8 W and 18.1 W, respectively. Seasonal analyses indicated that storks employed soaring flight more frequently in the latter half of the breeding season when they traveled to more distant sites. Energetic costs did not vary seasonally due to the increase in use of the energetically conservative soaring mode of travel on the longer flights. Observations at the colony indicated that foraging trip durations were constant throughout the season and that parents met increased nestling food demand by increasing the frequency of foraging trips.