Probability of Synanthropic Corvid Presence in the Western United States

Model of habitat utilization by synanthropic avian predators: common ravens (Corvus corax), American crows (Corvus brachyrhynchos), and black-billed magpies (Pica hudsonia). The former two species show increasing nation-wide population trends, and common ravens in the Mojave desert have been shown to have detrimental effects on threatened desert tortoise (Gopherus agassizii) populations. Power lines are used by common ravens and other raptors for nesting and as hunting perches. Linear features such as railroads, primary and secondary roads, and irrigation channels often serve as travel routes for these predators, and expand their movements into previously unused regions. Numbers of synanthropic avian predators increase in areas surrounding rural human developments, campgrounds, landfills, roads, rest stops, and agricultural lands because they provide reliable and often highly abundant food sources.
Using daily movement patterns, we developed a decaying probability function (P=100-100/1+e^5-0.3*Distance) which weighs areas near anthropogenic features more heavily (probability of occurrence equals 0.90 at 8km) than far (probability of occurrence less than 0.001 at 30km). We modeled the utilization of sagebrush landscapes by synanthropic avian predators using five spatial data sets: 1) populated areas, 2) campgrounds, 3) rest stops, 4) agricultural land, and 5) landfills; and one input layer: density of liner features. All spatial data sets and the one input layer were converted to distance input layers. Each GIS layer was buffered with a probability function derived from the daily movement patterns of corvid species.
Using each of the five-buffered layers, we created a composite layer by adding the probabilities of occurrence of each layer. This composite layer, therefore, is a measure of synergistic effects that enhance synanthropic predator dispersal in relation to the spatial distribution of anthropogenic resources.