EFFECTS OF HARNESS TRANSMITTERS ON BEHAVIOR AND REPRODUCTION OF WILD MALLARDS

Radio telemetry has been an important research tool in waterfowl studi es for >20 years, yet little effort has been made to evaluate potentia l effects of transmitters on the birds that carry them. As part of a 4 -year mallard (Anas platyrhynchos) study in the prairie pothole region of North Dakota and Minnesota, we compared radio-marked and unmarked female mallards in terms of percent time observed feeding, resting, an d preening; nest initiation date; and clutch size and egg volume. Radi o-marked females carried a 23-g back-mounted transmitter attached with a 2-loop harness (Dwyer 1972). On average, radio-marked females tende d to feed less, rest and preen more, initiate nests later, and lay sma ller clutches and eggs than unmarked females. Thus, behavioral and rep roductive data from ducks marked with back-mounted attached transmitte rs may be biased. We recommend that new designs of radio packages be f ield tested and caution that effects may be masked under extreme envir onmental conditions.