In 1983, Lewis Cowardin et al. published a paper which essentially reviewed a number of contemporary studies involving the nature of the recruitment problem (i.e., the rate at which hen ducks produce young for the Fall) in the prairie pothole region. Based upon the cornerstone that the existence of an annual surplus of ducks supports modern-day waterfowling, Cowardin determined that an important factor in the annual recruitment of ducks was nesting success (the proportion of duck nests which result in the clutch of eggs being hatched). The following were factors which Cowardin found to directly affect nesting success:

A. Weather. Weather has a major impact on nesting success for the simple reason that, in wet years it tends to produce good nesting conditions, while in drought years, it does just the opposite.

B. Manipulated Environment. Farming is the predominant activity which adversely affects duck production. Everything from tilled croplands, to drained potholes, to grazed grasslands, to haying operations, results in a lessening of annual duck production.

C. Predation. Probably the biggest reason for low nesting success stems from predation. Some 70% of all nest failures were attributed to predation. Indeed, it was even suggested that intensive farming enhanced predation inasmuch as it concentrated predator and prey activity in the remaining untilled habitats.

The management question which arose from this paper was: What impact does the high rate of nest failure and loss of hens and ducklings have on population size? It is suggested that in order to have a stable duck population, about 30% of the hens would have to be successful in one of their nesting attempts. For this to occur, nest success would have to be 15%, as compared to the 8% observed in the study.

Cowardin et al. suggested that studies indicated that managed habitat was far more productive (on a per area basis) than unmanaged areas, although, predators could still negate the positive aspects of managed habitat in some cases. However, in areas where predators were controlled, nesting success reached as high as 94% in some cases. Consequently, in light of the vagaries of the weather, and in spite of the manipulated environment (extensive farming), if the sport of waterfowling was to continue, the duck population must at least remain stable. In turn, this means that productive prairie pothole country will have to be managed in ways to make duck nesting success reach at least 15%.

Response of Nesting Ducks to Predator Exclosures & Water Conditions During Drought (1998)

In 1987, some four years after Cowardin's review article was published, and doubtless inspired by the research of their colleagues, Cowardin et al. initiated a 5-year study on the how small predator exclosures might assist in annual duck recruitment. The study was hampered by the onset of a drought which, unfortunately, was the same duration as that of the study. In turn, the drought caused Cowardin to slightly alter the nature of the study. In this regard, Cowardin attempted to determine whether there was a detectable increase over time in the proportion of nesting females in the exclosures. For four out of the five studied duck species, Cowardin found that over time there was a proportional increase in the number of nesting females within the exclosures.

Although unable to determine whether there was a higher incident of nesting ducks within the exclosures versus outside the exclosures, Cowardin et al. did, however, determine that nesting success within the exclosures was demonstrably higher, averaging an overall 72% success rate over five years. Further, Cowardin et al. concluded that predator exclosures offer the wildlife manager the opportunity to enhance waterfowl recruitment in the face of adverse conditions, including shrinking nesting habitat on unmanaged lands. Their results suggest that intensive management of small areas can increase duck recruitment from populations in larger surrounding areas.

Note: Both articles can be viewed on the NPWRC web site at:

"Problems & Potentials for Prairie Ducks"

"Response of Nesting Ducks to Predator Exclosures & Water Conditions During Drought"