Comparison of Condition Indices of Redheads From Different Wintering Areas

Abstract

Redheads Aythya americana concentrate annually in traditional wintering areas along the Gulf of Mexico coast from Florida to Tamaulipas, Mexico. We collected 399 redheads during two winters (1988-1989 and 1989-1990) from four traditional wintering areas in the United States: Chandeleur Sound (Louisiana), Redfish Bay (Texas), upper Laguna Madre-Baffin Bay (Texas), and lower Laguna Madre (Texas). Salinity, water depth, and human disturbance differed among these locations. We used metrics of ingesta-free body mass, whole skin mass, flight muscle (breast muscle) mass, and leg muscle mass, all corrected for body size, as indices to compare body condition of birds among the four wintering areas. Ingesta-free body mass and whole skin mass were greatest in the Louisiana and Redfish Bay birds, whereas flight muscle mass was greatest in birds from the upper Laguna Madre-Baffin Bay location. Leg muscle mass was greatest in birds wintering in Louisiana. Mean leg muscle mass was the only measure that did not increase significantly over the winter in any location, and leg muscle mass decreased in birds from two locations (upper Laguna Madre-Baffin Bay and lower Laguna Madre). None of the body condition indices increased over winter for birds from the upper Laguna Madre-Baffin Bay. Our findings demonstrate that redhead body condition indices, and hence nutrient reserves, vary among population segments from different bay and lagoonal systems on the Gulf of Mexico winter range. Consequently, site-specific environmental conditions may affect physical condition and fitness of wintering birds. Specifically, hypersaline conditions, combined with boating disturbance, through their influence on energetic costs from flying, swimming, and osmotic regulation, may explain differences in redhead body condition indices during winter. Failure to consider these factors during development of harvest regulations could be consequential for waterfowl population management.