Northern Prairie Wildlife Research Center Home Page. The strength of the correlation, however, declined from the 1950s to the 1980s. 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. 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. We suggest that declining availability of invertebrate foods and other reductions in habitat quality made cropped ponds less attractive breeding sites.