NESTING EFFORT BY WILD MALLARDS WITH 3 TYPES OF RADIO TRANSMITTERS

Although radio transmitters have been used extensively in waterfowl research for 20 years, effects of these devices on wild breeding mallards (Anas platyrhynchos) are largely unknown. Therefore, we compared various measures of nesting effort for mallards radiomarked with harnessed backpacks, sutured backpacks, and abdominal implants. The proportion of females that nested varied (P < 0.05) by transmitter type: 5 of 9, 16 of 16, and 5 of 5 females nested with harnessed backpacks, implants, and sutured backpacks, respectively. Females with harnessed backpacks initiated fewer (P < 0.0001) nests than birds with other transmitter types and devoted fewer (P = 0.007) days to egg laying and incubation than birds with implants. Our results suggest that studies using harnessed backpacks may underestimate nesting effort, hen success, and recruitment. We do not know whether implants provide accurate estimates of mallard nesting effort because we could not collect data for a control group without transmitters. We were able to monitor only 5 of 49 females fitted with sutured backpacks because 31 females shed sutured backpacks before the end of the nesting session. Although we had no evidence that sutured backpacks negatively affected nesting mallards, we do not recommend their use for such studies.