Field metabolic rate of wild turkeys in winter

Abstract

We investigated the winter bioenergetics of eastern wild turkeys (Meleagris gallopavo sylvestris) by measuring standard metabolic rate (SMR) and existence metabolism (EM) of captive turkeys and field metabolic rate (FMR) of free-ranging turkeys. Mean SMR and EM were 0.511 ± 0.040 mL O2·g-1·h-1 and 499.7 ± 17.7 kJ·kg body mass-0.734·d-1 (mean ± SE) as measured by indirect respirometry and food consumption, respectively. FMR was measured with doubly labeled water and was 10.5% higher in juvenile (0.976 ± 0.039 L CO2·kg-0.734·h-1) than adult turkeys (0.883 ± 0.034 L CO2·kg-0.734·h-1); their FMR:SMR ratios were 1.74 and 1.58, respectively. Juvenile turkeys weighed less and had less body fat (13.5%) than adults (18.9%). Mean FMR was lowest in 1996, when ground forage was unavailable and weather was more windy and cold than in 1995, when ground forage was available and the turkeys' activity and range were greater. Turkeys reduced FMR in 1996 by restricting movement and range, and using proximate shelter and supplemental food. We predict that juvenile turkeys are at an energetic disadvantage when food availability is restricted because of their higher FMR, lower body and fat masses, and higher activity costs than adults.