Effects of Carrying Radio Transmitters on Energy Expenditure of Pacific Black Brant

Abstract

We compared daily energy expenditure and body mass changes of captive yearling black brant (Branta bernicla nigricans) with and without backpack-mounted radio transmitters in a repeated measures design. Daily energy expenditure was estimated by continuously monitoring 0, consumption and CO2 production for 24 hours. Carrying transmitters had no effect on daily energy expenditure (P > 0.10) or mass loss (P > 0.3). We detected no temporal variation in daily energy expenditure after attachment of transmitters, an indication that any acclimation occurred within the first 24 hours. Because experimental birds were confined to a small (45 x 60 x 74 cm) chamber during metabolism measurements, our results do not address the influence of transmitters on the cost of locomotion. J. WILDL. MANAGE. 54(1):42-45 Radio telemetry has played a significant role in studies of waterfowl movements (Ringelman and Longcore 1982) and of mortality (Ball et al. 1975). However, results of studies relying on radio telemetry may be biased if the radio packages influence the individuals carrying them. Changes in waterfowl behavior have been associated with the application of radio packages (Gilmer et al. 1974), and Gilmer et al. (1974) detected an increased recovery rate for birds carrying radios compared to normally banded controls. However, Gilmer et al. (1974) could not separate the effects of harvest rate from a potentially higher reporting rate for radiomarked birds. Survival rate may be affected by application of radio packages if the energy budgets of marked individuals are sufficiently altered by the packages and harnesses. Such changes in energy budgets could result from behavioral changes (e.g., time spent feeding), changes in the costs of locomotion, including work required to carry the mass of the radio packages, or changes in metabolism associated with the stress of carrying a radio package. For example, birds secrete corticosterone in response to short term stressors, such as handling (Wingfield et al. 1982), and chronic factors such as social environment or climate (Assenmacher 1973, Wingfield et al. 1982). Corticosterone has a marked influence on metabolism (Assenmacher 1973) and, therefore, potentially on energy balance. No study has assessed the impact of carrying radio transmitters on daily energy expenditure of waterfowl. We had 2 goals: (1) assess whether attachment of backpack-mounted radio transmitters increased metabolic rate, and (2) determine whether black brant acclimated after attachment of transmitters, causing a temporal pattern in metabolic rate. To achieve our goals, metabolic rate was monitored periodically before application of radio transmitters and from 1 to 35 days after attachment. Our study does not address changes in energy expenditure associated with increased locomotory costs (Gessaman and Nagy 1988) in free-living black brant because our measurements were made on brant confined to metabolism cages. Black brant were reared in their natal areas during studies supported by the Alaska Fish and Wildlife Research Center and Yukon Delta National Wildlife Refuge, U.S. Fish and Wildlife Service. We thank M. R. Peterson, P. L. Flint, and K. Laing for assistance in rearing goslings in the field. N. A. Gundlach assisted with maintenance of brant in Fairbanks. K. J. Kokjer provided essential help with the maintenance of the data acquisition system. M. C. Perry, K. L. Parker, and K. J. Reinecke provided very constructive comments on the manuscript. Funding was provided by the Alaska Fish and Wildlife