Turns out, predator dynamics matter a lot to deer fawns in Pennsylvania

I’ve been thinking a lot about mammalian predators in Pennsylvania recently. Just finished writing a story about research using trail cams to assess the distribution and relative numbers of bobcats, coyotes, fishers, foxes and bears across the state. (The story will appear in the April 14 issue.)

They all kill and eat deer fawns, of course. That is what spurred the research. Pennsylvania game commissioners — knowing fawns here face only a 50 percent chance of seeing their first birthday — a few years ago asked for a predator study. The “camera trapping” research being done at Penn State is part of that.

While talking with researcher Asia Murphy, a doctoral student who is conducting a two-year project in which she has 88 trailcams in operation during the warmer-weather months, I learned some fascinating things about how predators deal with each other.

One example, coyotes kill bobcats, and hence bobcats avoid them and areas where coyotes are numerous. And scientists know that coyotes are more efficient predators of young fawns. So if bobcats are avoiding an area because there are coyotes there, it might be a better area for older fawns.

And fishers seem to be a wildcard for fawn mortality. Because they were not present in the state for so long before they were reintroduced, wildlife scientists really have no idea about their predatory impact.

The arrival of coyotes in the state appears to have upset the forest ecosystem in surprising ways. In fact, scientists now strongly suspect their dominance is contributing to the epidemic of Lyme disease. Lyme is spread by deer ticks, and their main vector is the white-footed mouse, whose population is exploding right now, fueled by ample mast crops.

The main predator of those mice is the red fox, but fox numbers are way down, likely because coyotes kill foxes and crowd them out of favored habitats.

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