| Northern Pintails (Anas acuta) are below population goals and low survivability or reproductive success has contributed to population decline. Survivability and reproductive success are related to lipid reserves accumulated on wintering grounds and spring stopover sites, where quality and quantity of food resources are essential to maintain body condition. Birds that arrive on breeding grounds in good body condition have higher reproductive success, thus by understanding lipid reserves at stopover sites, management can be targeted to improve condition of female Northern Pintails. To elucidate the relationship within the Rainwater Basin, an important stopover site in south-central Nebraska, I measured whole body composition and plasma lipid metabolites of female Northern Pintails during spring migration and evaluated their relationships with age class, date collected, and region collected. Eighty female Northern Pintails were collected each spring in 2012 and 2013. Among after hatch year (AHY) birds, there was a relationship between both total fat and percentage of fat to date collected (r = 0.27, P = 0.022; r = 0.28, P = 0.015; respectively). Birds that arrived early had more fat and percentage of fat. Among hatch year (HY) birds, there was a relationship between both triglycerides and beta-hydroxybutyrate to date collected (r = 0.29, P = 0.007; r = 0.27, P = 0.014; respectively). Triglyceride levels were higher and beta-hydroxybutyrate levels were lower for HY birds that arrived early. I found that for birds that arrived early, AHY birds had greater lipid reserves and HY birds are better able to exploit food resources and gain lipid reserves. Better body condition of early arriving AHY birds and better ability of early arriving HY birds to acquire lipids enables early birds as a whole to move to breeding grounds and be more reproductively successful. |
