Background/Question/Methods We synthesized information on foraging and energetics of Whooping Cranes (
Grus americana) wintering in Texas via development of a simulation model. The model, which we formulated as a compartment model based on difference equations (
Dt = 1 day), represents daily energy expenditure (DEE) and intake (DEI), and the resulting energy balance, of an individual crane while on the wintering grounds in Texas. We represented DEE as basal metabolic rate, calculated as a function of body weight, adjusted for the energy costs of activity in each of four habitats: salt marsh vegetation, open water within the salt marsh, upland, and bay. We represented DEE in each habitat as a function of the time spent in each of six activities; feeding, locomotion, interaction, rest, alert, and maintenance, and the energetic cost of each activity. We calculated DEI as the average intake across the four habitats, weighted by the proportion of daylight hours spent in each. We represented DEI in each habitat as a function of the intake rate, mass, gross energy, and metabolizable energy coefficient of each type of food item; wolfberries in salt marsh vegetation, blue crabs in open water within the salt marsh, insects in the upland, and clams in the bay. We parameterized the model based on field data and other information presented by Chávez-Ramírez (1996).
Results/Conclusions With this parameterization, the model simulated the energetic budget of Whooping Crane’s overwintering period on the Texas coast during the months (October – April) and compared overall energetic budgets between two different winters 1992-93 and 1993-94. The model estimated DEE reasonably, but overestimated DEI for both years. The DEB simulated showed a Whooping Crane with higher energetic balance than observed. The simulated energetic contribution of different food items to the daily and overall winter diet of Whooping Cranes was very close to observed, however blue crabs intake simulated was higher in the second winter than observed. It was estimated and simulated differential daily energy budgets (DEB) and potential for energy storage based in fat accumulation to evaluate predictions regarding overwinter survival and reproductive success during different years of study. We use this model as a point of departure to simulate the effects on daily energy balance of shifts in foraging activity and habitat use, based in different scenarios of food availability in the wintering ground.
