Nutritional ecology of northern pintails wintering in the Laguna Madre of Texas

Abstract

Molt intensity, digestive tract morphology, diet, and carcass composition of northern pintails were investigated along the southern Texas Coast during winters of 1997-98 and 1998-99. Precipitation was 133% and 83% of the long-term average during 1997-98 and 1998-99, respectively. Prealternate molt was less intense during winter of the wet year compared to the dry year and may have been initiated earlier. Pintail diets were dominated by plant material during most seasons. Foods consumed by pintails in the Laguna Madre were low in fat, protein, and true metabolizable energy relative to foods consumed by pintails in freshwater habitats. Gammarus was the most digestible food consumed and provided the greatest energy/g of dry mass. The overall diet of pintails during winter provided from 0.44 to 1.38 kcal/g of TMEN and was notably of lower quality during the dry year compared to the wet year. The diet of pintails wintering along the southern Texas Coast appears to provide considerably less energy than diets of pintails wintering in freshwater habitats. Most reductions in mass of digestive tract occurred from early December through February and appeared to result from catabolism of lean tissue and not from changes in diet quality. Lipid reserves were catabolized throughout winter both years, however, a simultaneous decline in lean body mass during the wet year resulted in percent fat remaining constant. In the dry year, fat was reduced (P < 0.001) by >63% between October and the end of February. Somatic protein significantly declined throughout winter both years (P < 0.001) and pintails departed the Laguna Madre approximately 200 g lighter than has been reported for pintails departing rice habitats in California. Continued reductions in freshwater and rice habitats along the Texas Coast may negatively impact pintail populations in Texas if pintails shift their winter distribution to saline, coastal habitats that appear to provide poorer quality diets and result in birds departing wintering grounds in impoverished body condition. However, pintails wintering in freshwater habitats in western Texas were reported to exhibit similar patterns in nutrient reserves to pintails wintering in the Laguna Madre which may indicate an adaptive strategy during winter.