Grays Lake Ecosystem. Comparison of Wetland and Upland Management Practices at Grays Lake National Wildlife Refuge ? Predator Observations

Authors(s): J. Austin

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Publication Date: 0000-00-00

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Abstract: As part of the habitat management study, we want to assess whether there are differences in nest success among four different treatments. Removal of vegetation, whether by grazing or burning, can affect nest success because it reduces the amount of cover for nests, making nests more visible and therefore more vulnerable, to predators. Predation is the most common cause of nest failure. However, predators may not be equally distributed across the whole area of interest, and different predators can have different impacts on nesting birds. For example, a field falling within a coyote's territory likely will have higher duck nest success than one within a red fox's territory because fox are more likely to take both nest and nesting hen. Fields containing a fox den will probably have very poor nest success because of the high level of fox activity and their food requirements. Thus objective interpretation of nest success results requires an understanding of the predator community and areas of activity. Scientists at Northern Prairie have developed a simple index of the predator community to use in conjunction with nesting studies, based on daily observations of field personnel. At the end of each day in the field, each person completes a simple form noting how many places they observed species known to prey on nests or nesting birds; the area of observations includes the entire Grays Lake basin. Predators recorded include badger, skunk, mink, weasel, red fox, coyote, great-horned owl, short-eared owl, buteo (various hawks), northern harrier, falcon, eagle, raven, crow, magpie, and other. All observations are summed as number of observations per hour of observation, providing a monthly and annual pattern of predator activity. Observations of mammals are plotted on maps to assess main areas of activities. Although there are some biases (e.g., coyotes are rarely observed), overall this method provides good insight into the distribution of predator activities. Over the 4 years of the study, we collected 11,381 hours of predator observations (1,767 hr in 1997, 2,434 hr in 1998, 3,874 hr in 1999, and 3,306 hr in 2000). The most commonly observed predators were buteos, crows, ravens, northern harriers, and red fox. Other predator species recorded included mink, least weasel, raccoon, great-horned owl, magpie, golden and bald eagles, peregrine and prairie falcons, domestic cats and dogs, bobcat, and mountain lion. Of mammalian predators observed, skunks and red fox were most commonly observed, particularly in spring when the females were denning and actively searching for food for their dependent young. These two species were observed in all the experimental units, and were most commonly observed in those units immediately west of the refuge headquarters. Patterns of plotted observations for fox and coyote suggest their distributions changed over the 4 years of the study. Buteos, harriers, and corvids were the most common avian predators observed, with >0.250 observations/hr on average. These species all showed strong seasonal patterns, which may be related to movements of migrant birds through the basin (high numbers in early spring or fall) or reduced movements during nesting (May-June). Migrant buteos appear to usually move through the area during a 2-3 week period during late April-early May. Eagles (mostly bald eagles), although not common, also showed similar pattern suggesting movement of migrants through in April-early May. The particularly high observation rates of buteos and corvids in 1998 and 1999, and increased observation rates of skunks in 1999, may be related to the high availability of microtines in those springs. We cannot directly attribute nest losses to any particular predator in this study. However, results from this and other studies indicates that predator impacts on nesting birds are affected by a number of factors, including seasonal change in predator numbers and activity patterns, predator territories, den site locations, alternate prey, and water levels. At Grays Lake, higher water levels in most springs probably limit movements and access of mammalian predators in wet meadow areas, and also serve to concentrate small mammal populations on higher ground. Various habitat management techniques, such as elimination of spoil banks near stock ponds, may be used to minimize impacts of predators on nesting birds on refuge lands.

Keywords: Idaho, Gray's Lake, ecology, predation, habitat, nest, nesting, population, mortality, management, animal, bird, Aves, Anatidae, ornithology, duck, waterfowl, water bird, mammal, Canidae, Canis latrans, coyote, canine, fox, red fox, Vulpes vulpes, food, badger, Mustelidae/Taxidae/taxus, skunk, Mustelid, Mephetis mephitis, mink, Mustela vison, weasel, Mustela frenata, owl, great-horned owl, Bubo virginianus virginianus , raptor, accipter, short-eared owl, Asio flammeus, buteo, hawk, northern harrier, Circus cyaneus, falcon, peregrine falcon, Falco peregrinus, eagle, raven, Corvus corax, crow, Corvus brachyrhynchos, magpie, Pica pica, least weasel, Mustela nivalis, raccoon, Procyon lotor, golden eagle, Aquila chrysaetos, bald eagle, Haliaeetus leucocephalus, prairie falcon, Falco mexicanus, bobcat, Felis rufus, mountain lion, cougar, puma, Felis concolor, feline, Felidae, forage, Corvidae, harrier, Circus cyaneus, migration, microtine, rodent