A third limiting factor for Great Lakes mallards was over-winter survival of hens. This had a much greater effect on mallard populations in the Great Lakes states than on the prairies (see pie chart comparison). Although this was not directly measured in this study, DU researchers had to determine annual and seasonal survival rates to conduct complete life-cycle analyses of the birds. Band-return data were used as well as survival estimates from radio-marked hens monitored in the study. Overall, the researchers found that annual survival among female mallards from the Great Lakes states was approximately 51 percent, slightly lower than the 58 percent annual survival estimated among prairie-nesting mallards. Breeding survival among female mallards during the summer also was not really that different—75 percent in the Great Lakes states compared to 72 percent on the prairies. However, the difference in over-winter survival between the two groups was dramatic. Only 69 percent of hen mallards from the Great Lakes states survived the winter, compared to 80 percent of prairie-nesting mallards. Generally, two factors have the greatest influence on over-winter survival: wintering habitat conditions and harvest.
What does all this mean for waterfowl habitat programs in the Great Lakes states? In the Prairie Pothole Region, inadequate grassland habitat is a major factor limiting duck production. In the Great Lakes, the foundation for breeding habitat delivery has always been based on research from the prairies, which led to a heavy emphasis on grassland restoration accompanied by wetland restoration. Now, findings from the Great Lakes study have prompted DU to change its habitat-delivery philosophy in the region to focus more on wetland restoration and less on grassland conservation. This does not imply, however, that grasslands are unimportant, because on some landscapes where nest success has fallen below 15 percent, the restoration of grasslands will be needed to improve mallard production.
To help field biologists deliver the best habitat conservation programs in specific areas, DU has used data from the study to develop the Habitat Evaluation Network, affectionately known as HEN. This is a complex modeling program using geographic-information-systems technology that recommends the best habitat-management scenario, based on current landscape conditions. For example, when a landowner asks DU what he or she should do for the ducks, HEN will provide DU biologists with several key pieces of information, including whether or not there are former wetlands on the landowner's property that can be restored, the composition of the surrounding landscape, and what is likely the best strategy to improve mallard production on the property. In a nutshell, HEN will provide DU with the information required to customize habitat restoration and protection plans for individual landowners throughout the region.
Although Great Lakes mallards face the same limiting factors and threats as their prairie brethren, the relative importance of these factors is not the same. We now know how to address these challenges through habitat conservation programs improved by science. Instead of Grasslands for Tomorrow, a crucial DU conservation program on the prairies, the Great Lakes region needs Wetlands Forever!