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Wetland Preferences of Prairie-nesting Mallards: Implications To Settling Patterns and Population Trends

Gary Krapu and Ray Greenwood


Waterfowl biologists have long noted that duck production in the Prairie Pothole Region (PPR) increases markedly in wet years and that mallard breeding population size is correlated with the number of May ponds counted the previous year. The strength of the correlation, however, declined from the 1950s to the 1980s. To gain insight into the underlying factors controlling the relationship between mallard production and May pond density and to understand why the correlation has declined, we examined wetland habitat preferences of radio-marked females and effects of land use on settling patterns of unmarked pairs in prairie pothole habitat from 1987-91.

We found that radio-marked females used semipermanent ponds most but preferred temporary and seasonal ponds when available during prenesting and egg production. The number of ponds used by individual females varied by year, by reproductive stage, and with pond density during egg production. The preference of females for temporary and seasonal ponds during egg production probably reflects, in part, greater availability of aquatic invertebrates in these shallow ponds. Invertebrates supply most of the protein needed for egg production. As density of ponds increased, individual females used more ponds and presumably were more successful at avoiding competition for food resources.

Female mallard and ducklings
In North Dakota, scientists found that radio-marked female mallards used semipermanent ponds most but preferred temporary and seasonal ponds when available during prenesting and egg production.

Most temporary and seasonal wetland basins in cropland are tilled when dry. To assess whether the declining correlation between number of May ponds and mallard production might be linked to degradation of shallow ponds, we compared settling patterns of pairs to land use during 1987-91. When temporary/seasonal pond area was low due to drought, we found no relationship between number of settled pairs and percent of landscape in cropland. However, as temporary/seasonal pond area increased, number of pairs varied inversely with percent of landscape in cropland. We suggest that declining availability of invertebrate foods and other reductions in habitat quality made cropped ponds less attractive breeding sites.

In eastern North Dakota from 1963-85, a 34% decline occurred in number of breeding mallard pairs relative to May ponds. The declining correlation between pairs and ponds came during a period of major increase in cultivation of planted and native grassland in North Dakota. With the end of the Soil Bank Program in 1970, about 10% of the State's cropland that had been planted to perennial cover in the late 1950s was brought back into grain production. Along with this change, a large acreage of native pasture and hayland was converted to cropland when grain prices soared, beginning in 1973 following a large wheat sale to the Soviet Union. A similar trend in cropland expansion occurred across the prime breeding range of the mallard in prairie Canada. We conclude degradation of shallow wetland habitat leading to pair displacement into less productive habitats together with lower nest success rates as the percentage of landscape in cropland increased across vast areas of the PPR were major factors contributing to the decline in correlation between number of May ponds and mallard abundance.


This resource is based on the following source:

Krapu, Gary and Ray Greenwood.  1997.  Wetland Preferences of Prairie-nesting Mallards: Implications to Settling Patterns and Population Trends.  Waterfowl 2000 10(1):12.

This resource should be cited as:

Krapu, Gary and Ray Greenwood  1997.  Wetland Preferences of Prairie-nesting Mallards: Implications to Settling Patterns and Population Trends. Waterfowl 2000 10(1):12.  Northern Prairie Wildlife Research Center Online.  http://www.npwrc.usgs.gov/resource/birds/wetpref/index.htm (Version 16JUL97).


For more information, write to Gary Krapu or Ray Greenwood, U.S. Geological Survey, Northern Prairie Science Center, 8711 37th Street SE, Jamestown, North Dakota, or call (701) 253-5500, or fax (701) 253-5553.


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