Monday, March 01, 2010

Drought and Birds: Mallard

Gary L. Krapu, Albert T. Klett, and Dennis G. Jorde (1983) studied reproductive strategies of Mallards breeding in the prairie pothole region of North Dakota under the variable spring water conditions characteristic of that region. Specifically, they examined "population patterns in eastern and central North Dakota over a 20-year period and examined factors responsible for observed densities and reproductive effort under a broad range of wetland habitat conditions."

In summarizing the results of this important study, I can do no better than provide the authors’ Abstract in full:
Mallard (Anas platyrhynchos) breeding densities in the prairie pothole habitat of eastern North Dakota during 1961-1980 varied from 2.28 birds/km2 in 1977 to 9.47 birds/km2 in 1963 [a factor of 4.2] and were correlated with pond abundance (r = 0.543, P < 0.05). The number of basins used by pairs declined with drought, as did home-range size. Nesting activity also varied with the number of ponds holding water/km2, ranging from high (including substantial renesting) under favorable water conditions to low during extreme drought. The span between first and last nest initiations declined by 19 days from a wet to a dry year. With severe drought conditions during spring 1977 on the Medina Study Area, pairs returned to attempt nesting but were unsuccessful, and most abandoned activity centers by mid-May. Although the average clutch size declined by about 0.7 egg[s] from a wet to a dry year on the Interstate Study Area, hatchability of eggs remained constant. We describe the adaptive strategy of Mallards for breeding under variable water conditions and food resources in the semiarid environment of mid-continent North America.
Thanks to SORA (the Searchable Ornithological Research Archive) this paper may be read in full by clicking on the title highlighted below.

Citation:

Krapu, Gary L., Albert T. Klett, and Dennis G. Jorde. 1983. The effect of variable spring water conditions on Mallard reproduction. Auk 100: 689-698. [.PDF]

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