Gary L. Krapu
D.A. Brandt
R. R. Cox Jr.
P.J. Pietz
2003
<p><span>Waterfowl biologists need reliable predictors of </span>brood<span> and </span>duckling<span> </span>survival<span> to accurately estimate recruitment rates. We examined 30-day </span>survival<span> rates of </span>gadwall<span> (Anas strepera) broods (1992-1994) and ducklings (1990-1994) </span>in<span> eastern North Dakota, USA, during years when water conditions ranged from extremely dry to extremely wet. We evaluated effects of several variables on </span>brood<span> </span>survival<span>: (1) percent of seasonal wetland basins containing water, (2) occurrence of rain on the current or 2 previous exposure days, (3) minimum ambient temperature averaged over the current and 2 previous exposure days, (4) hatch date, (5) </span>duckling<span> age, and (6) </span>brood<span> size. Only 9 of 58 radiomarked females lost their entire broods; Kaplan-Meier 30-day </span>survival<span> rate for broods was 0.84. </span>Brood<span> size (adjusted for hatch date) was a better </span>brood<span>-</span>survival<span> predictor than were any of the environmental variables. Risk of total </span>brood<span> loss decreased by 24% for each additional </span>duckling<span> </span>in<span> the </span>brood<span>. We monitored fates of 212 radiomarked ducklings from 94 broods. Daily risk of death for ducklings was twice as high when seasonal ponds were scarce as when ponds were abundant. </span>Duckling<span> </span>survival<span> rate was lower during the first 7 days of life whether it rained or not; </span>survival<span> rate was greater for 8- to 30-day-old ducklings, but was reduced by rain. Thirty-day </span>duckling<span> </span>survival<span> was greatest when minimum daily temperatures exceeded 10°C and no rain occurred. We attributed 86% of 87 deaths of radiomarked ducklings to predation; American mink (Mustela vison) accounted for ≥68% of the 40 deaths for which predator type could be ascertained. Despite apparent resilience of </span>gadwall<span> populations during drought, our study documented a positive effect of seasonal wetland availability on </span>gadwall<span> </span>duckling<span> </span>survival<span>. Management efforts to improve recruitment will be more effective </span>in<span> years when most seasonal basins contain water.</span></p>
application/pdf
10.2307/3802714
en
Wildlife Society
Factors affecting gadwall brood and duckling survival in prairie pothole landscapes
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