Energetic reserves of Hudson Bay willow ptarmigan during winter and spring

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Abstract
Willow ptarmigan (Lagopus lagopus) were collected from the Hudson Bay coast of Ontario from February to June, and the proximate composition and tissue composition of the carcasses were analysed. Total carcass composition remained uniform from February to late May. The neutral fat level remained low at approximately 2% of body weight. The total energy reserve from neutral fat and labile protein was calculated to be 165 and 180 kcal (1 kcal = 4.1868 kJ), respectively, for a 550-g female and a 600-g male ptarmigan. Gonadal recrudescence began in early May, but its extent was not correlated significantly with change in body weight or carcass neutral fat content. The low neutral fat levels observed during winter and the onset of reproduction indicate that this population is dependent upon its immediate food supply for both winter survival and clutch formation.