Effects of anthropogenic and environmental stress on the corticosterone levels of wintering Northern Pintails (Anas acuta)

Winter-specific survival rates for female Northern Pintails (Anas acuta L., 1758; hereafter "Pintails") at the Bosque del Apache National Wildlife Refuge were found in a previous study to be low relative to other wintering areas, raising concerns that tourism could be impacting the health of the population. Measurements of corticosterone levels enable the assessment and quantification of human-induced stressors that can ultimately affect fitness. We analyzed corticosterone concentrations and the relationship between body condition and maximum stress-induced corticosterone in areas with and without tourism access. Female Pintails were captured in winters of 2008-2009 and 2009-2010. The corticosterone response was similar between areas with and without tourism, but different between winters. In mid-January 2010, levels were 73% greater after 60 min compared with those in 2009. A greater stress response in mid-January 2010 may have been due to colder temperatures and arriving later and in poorer condition. Also in 2009-2010, there was a negative correlation between carcass fat and maximum corticosterone, possibly in response to colder temperatures, arriving in poorer condition, or a combination of both. Our study indicates that in mid-to late winter, activity of the hypothalamic-pituitary-adrenal axis may be higher during winters with comparatively greater environmental hardships, emphasizing the importance of carefully managing waterfowl during periods when they are most sensitive.