Mallard Brood Survival in Prairie Pothole Landscapes

		"The importance of seasonal water to mallard brood survival underscores the need to conserve or restore seasonal wetlands as a major component of wetland complexes managed for dabbling duck production."
Total brood loss for mallards is 5 times more likely during rainy conditions than during dry periods.

Waterfowl managers need effective and economical means of estimating annual duck production on public and private lands in the Prairie Pothole Region. Brood survival is one of the most critical but least understood components of mallard production.

Therefore, we sought to identify key factors influencing mallard brood survival and to develop a model for predicting brood survival rates. Information was obtained by monitoring radio-marked broods and ducklings at several locations in eastern North Dakota and west-central Minnesota during a series of dry (1988-92) and wet years (1993-94). Variables evaluated were percent of seasonal wetland basins with water, percent of upland landscape in perennial cover, ambient temperature, rainfall, hatch date, brood age, age of brood female, and brood size. Radio-marked broods were monitored daily from hatch through 30 days of life.

Total brood loss occurred in 16 of 56 broods monitored during the study. Our final-fitted model of brood survival contained only main effects of percent of seasonal basins with water, hatch date, and rainfall. Total brood loss was 11 times more likely when broods were located where less than 17% of the seasonal basins contained water than where greater than 59% of seasonal basins were wet. Total brood loss was 5 times more likely during rainy conditions than during dry periods, and the risk of total brood loss increased by 5% for each 1-day delay in hatching between 17 May and 12 August.

Our results suggest that whether or not seasonal wetlands contain water strongly influences survival of mallard broods and thus mallard production in the Prairie Pothole Region. Ducklings in landscapes where most seasonal wetlands are wet are less vulnerable to mink and other aquatic predators that prefer permanent water. Mink, the most effective predator of ducklings in many parts of the Prairie Pothole Region, are dependent on wetland-derived prey for survival. As a result, few mink survive severe droughts in landscapes lacking permanent water. Low mink densities and an abundance of seasonal ponds likely contributed to high brood survival (greater than 90%) in 1993-94.

Water conditions also affect availability of food for growing ducklings. In drought years when few seasonal ponds are available, ducklings spend more time searching for food, have lower rates of food intake and growth, and must travel longer distances overland between ponds. As a result, starvation and predation of ducklings probably increase during drought.

Waterfowl managers can use the final-fitted model resulting from our study as a tool for predicting mallard brood survival for areas in the Prairie Pothole Region. Using tables at http://www.npwrc.usgs.gov/resource/broodsrv/broodsrv.htm, managers can obtain predicted brood survival rates and associated standard errors for various levels of seasonal basins with water, hatch dates, and rain.

The importance of seasonal water to mallard brood survival underscores the need to conserve or restore seasonal wetlands as a major component of wetland complexes managed for dabbling duck production. Because early hatched broods survive at higher rates, management efforts directed toward improving success of early nests can increase recruitment of mallards especially during wet years.