Seasonality in the feeding ecology of Black-necked swans (Cygnus melancoryphus) in a temperate wetland of southern Chile

Abstract

The concomitant effects of environmental physical constraints associated with the availability and quality of food will finally affect the energy budget of wild animals. This study aimed to determine the effect of seasonality on water level, behavioural and nutritional status of Black-necked swans inhabit the Budi Lake, Chile. In winter and spring, the water level was recorded using a graduated rod and a time budget of 60 swans/hours was recorded from 8 am to 6 pm using binoculars and the focal method. In order to determine nutritional status a subset of 20 birds were captured and weight, length, wingspan, and tarsal length were measured. Also, blood sample was collected to determine cholesterol, triglycerides, and total proteins plasma concentrations. Budi Lake’s water level increase in winter (111 ± 3 cm vs 54 ± 0.6 cm, P = 0.04). In addition, winter swan population increased significantly the time allocated to foraging at morning, and the proportion of effortful foraging behaviour (37/222 vs 14/185, P = 0.01), assigning less time to resting activities (7 ± 4 % vs 11 ± 2 %, P = 0.05) compared with spring population. Nutritional status was not compromised in swan populations in both seasons. In conclusion, behavioral adjustments allow Black-necked swan populations to maintain an adequate nutritional status despite the increase in water level during winter season.