Importance to waterfowl
Despite the habitat degradation that has occurred across the PPR in the last century, this region continues to be the most important to breeding waterfowl in North America. In wet years, 70% or more of the continent’s duck production originates in the PPR (Fig. 1). It is especially important on a continental basis to breeding northern pintails, mallards, canvasbacks, redheads, gadwall, blue-winged teal and northern shovelers. Although populations across the Canadian prairie and parkland have not responded to the levels expected, the relatively wet years experienced during the 1990s have resulted in most of these species reaching and surpassing the regional population goals as established by the NAWMP. One exception has been the northern pintail. This grassland-dependant duck has struggled despite the generally favorable water conditions in the last decade. Studies show that breeding pintail populations have decreased in excess of 50% in the last 20 years, with no significant improvement to the trend. The shallow, nutrient-rich wetlands and fragile grasslands on which these birds rely have been impacted particularly hard despite recent improved moisture conditions.
Lesser scaup are another species that has historically relied on the PPR for breeding habitat, particularly in the northern portion of the region where the prairie/parkland transitions to the mixed-wood boreal forest. Again, despite the favorable moisture conditions experienced in the last decade, scaup have not responded with improved breeding success. As a result, scaup are hovering at population levels below those established under the NAWMP as plan goals.
Several million ducks and geese pass through the region each spring. Even in regions that have experienced substantial wetland losses, such as Iowa, valuable migration habitat is often available in early spring when the ground is still frozen and drainage ditches are not yet flowing. In autumn, an estimated 8 - 10 million ducks and 0.5 - 1 million geese migrate south through Iowa, en route to warmer climates. A few, including an average 106,000 ducks and 138,000 geese, remain during winter in the PPR or adjacent areas. However, the PPR is most critical for breeding waterfowl.
Fig 1. Total ducks observed in the May survey in the Prairie Pothole Region.
Recruitment rates, defined as the number of young female ducks that enter the fall population per the number of adult females in the spring population, are highly variable within the PPR. However, there is a strong relationship between recruitment and the quality and amount of upland cover. In recent years recruitment rates and brood production in the U.S. portion of the PPR have exceeded those in Canada (Fig. 2). This change from historic patterns is thought to be a result of exceptional precipitation and excellent upland conditions in the U.S., primarily due to an initiative called the Conservation Reserve Program (CRP). In the U.S. PPR, recruitment rates have been estimated for each of the USFWSs Wetland Management Districts. Those simulations, made as part of the Multi-Agency Approach to Planning and Evaluation, revealed that 9 of the 14 Districts had recruitment rates above the maintenance level of 0.5 needed to sustain or increase duck populations. These simulations were made assuming the current distribution of CRP land.