Carcass Composition and Digestive-Tract Dynamics of Northern Pintails Wintering Along the Lower Texas Coast

We collected 341 northern pintails (Anas acuta) along the lower Texas coast, USA, to investigate dynamics of carcass and digestive tract components during winter to help assess the ability of this region to support wintering pintail populations. Pintails relied more on endogenous lipid and protein reserves during winter of a dry year than a normal to wet year. Carcass fat remained relatively stable during the wet winter; however, pintails catabolized approximately 65% of their lipid reserves between arrival in October and departure at the end of February during the dry winter. Somatic protein mass also declined over both winters as pintails catabolized up to 20% of their muscle mass. Gizzard atrophy explained most of the changes in somatic protein during the wet winter, whereas catabolism of breast muscle also contributed to changes in protein mass during the dry winter. Ingesta-free digestive tract mass was greatest in early December, and then declined abruptly through February during both winters. Pintails departed the lower Texas coast in late February approximately 20% lighter in body mass than when they arrived in autumn. Mid-continent pintails may frequently opt to winter in southerly latitudes where they can maintain minimal endogenous reserves due to the moderate climate, limited human disturbance, and relatively dependable, but often lower-quality food resources. However, potential consequences of pintails initiating spring migration with reduced energy reserves include greater reliance on spring staging and breeding areas to meet their nutrient requirements for migration and reproduction, later arrival on breeding grounds, and reduced survival and reproductive success. Nutrient reserve dynamics of wintering, mid-continent pintails support the need for enhanced conservation of productive spring staging and breeding habitats for this population. It also provides additional concern over the loss of productive wintering sites along the western Gulf Coast.