Resting Metabolic Rates of Adult Northern Shrikes (Lanius excubitor) Wintering in Northern Wisconsin

Resting metabolic rate (RMR) represents a significant component of an animal’s energy budget and is correlated with ecological, physiological, and life-history parameters. We measured resting metabolic rates of 14 adult Northern Shrikes (Lanius excubitor) wintering in northern Wisconsin (Ashland and Bayfield Counties) over a 2-year period (Jan–Apr 2008 and 2009). The average (±SE) RMR was 3.09 ± 0.45 ml O2/g/hr (range 2.46–3.83) from the first reported RMR values for adults of this species from the Neartic. Our RMR values were 50% higher than RMRs gathered from summer adult Northern Shrikes in the Paleartic. These data suggest Northern Shrikes exhibit seasonal variation in their RMR as a potential means of winter acclimatization.