Radio-telemetry increases free-living energy costs in the endangered Takahe Porphyrio mantelli

Abstract

An assumption of most radio-telemetry studies is that the technique does not affect the behaviour or physiology of the study animal in any important way. However, previous work has shown that radio-tags can elevate the energy costs of activities such as flying and swimming, which may have implications for survival. Using an experimental approach, we assess the impact of tag-bearing on the free-living energy expenditure of a large, relatively inactive, non-swimming bird: based on previous assumptions, it would be expected to be trivial. Daily energy expenditure increased by 8.5% in the flightless Takahe when they were carrying radio-tags. We can rule out several potential sources of elevated living-costs due to tags, and conclude that a greater thermoregulatory effort was likely to be the main factor involved. This increase in energy expenditure could potentially reduce survival in this endangered species, particularly in its montane habitat in winter.