Landscape ecology of mammalian predators and its relationship to waterfowl nest success in the Prairie Pothole Region of North Dakota

摘要

Mammalian predation is a major cause of mortality of breeding waterfowl in the Prairie Pothole Region. However, little is known about how landscape features influence the ability of predators to find waterfowl nests. I analyzed the habitat selection and movement patterns of radiomarked red fox ( Vulpes vulpes) and striped skunk (Mephitis mephitis) in two 41.4 km2 study areas with contrasting compositions of grassland (planted cover, pastureland and hayland). The study areas included either 10--15% (Low Grassland Composition, LGC) or 40--50% (High Grassland Composition, HGC) grassland. Edges of wetlands surrounded by cropland were consistently selected by fox and skunk on both types of landscape. Foxes frequently selected planted cover (both edge and interior areas) in LGC landscapes, whereas they rarely selected the interior areas of planted cover in HGC landscapes. Fractal analysis indicated that fox pathways were slightly straighter in LGC landscapes suggesting increased traveling behavior in the more prevalent cropland. However, there were more frequent sharp turns (characteristic of searching behavior) within planted cover in LGC landscapes. Contrary to predictions, the rate of movement was not slower when animals where in planted cover compared to when they were in cropland in either type of landscape. Furthermore, the frequency of turn angles was highly variable in cropland. In contrast, skunk pathways did not differ between LGC and HGC landscapes. They were more influenced by wetlands than by the landscape composition of grassland. Skunks spent more time in back and forth movement in all habitats. The rate of movement was faster in cropland than in planted cover in LGC but not in HGC landscapes. When I simulated random combinations of predator movement and waterfowl nests there was essentially no relationship between planted cover patch size and the predicted proportion of nests that would be encountered by predators. However, the observed proportion of nests encountered by predators in intermediate sized patches (50--120 ha) was frequently greater than the proportion predicted by random activity. This study has led to a refined understanding of how predators perceive the landscape and is an important contribution to both predator landscape ecology and waterfowl management.