Urban Deer

White-tailed deer, Massachusetts Ave, Washington, D.C.  (c) MMD, 2016

 

We took the dogs for a nice, long walk one evening last week, and as we were headed up Massachusetts Avenue (the “Embassy Row” stretch), we came across a group of deer grazing at the side of the road. They watched us, but never seemed too concerned, even though both of our (large) dogs were excited and one was barking her head off at them! Urban white-tailed deer have become quite overabundant in many urban areas in the eastern US. This has happened for a variety of reasons — for example, we tend to create ideal habitat for them, as they do well in edge habitat (in this case, the “edge” between forested areas and non-forested, grassy areas. The area in this photo is edge — grassy area up to the sidewalk, with a small forested area behind it). And of course they have few, if any, natural predators left (there’s some debate about how coyotes and deer interact, at least in the mid-Atlantic region).

When predators are missing, we sometimes find trophic cascades, an ecological process where herbivores become over-abundant and eat more plants, which can dramatically change the landscape. We often think of two main mechanisms when talking about trophic cascades: overabundance of herbivores because of a lack of hunting, and increased grazing because of a lack of fear. To that second point, some ecologists have written about an “ecology of fear” — when predators are present, herbivores remain more vigilant, scanning the landscape for predators. Because of this, at least some reduce their foraging (one 2001 study that looked at Yellowstone National Park before and after wolves were reintroduced there determined that female elk with calves were most likely to increase their vigilance). There’s also evidence to suggest that some herbivores change where they feed, spending less time in areas where they’re more vulnerable (for example, in areas where their view of the landscape is limited by natural features). I’d argue that the deer in DC are no longer really afraid of predators (or pretty much anything else), given their reaction to the dogs!

Hunting is a commonly suggested alternative to natural predators. While hunting can reduce the number of animals, can it mimic the fear that herbivores have of predators? One study (Cromsigt et al., 2013) suggested that human hunting should mimic predatory hunting more closely to get the same results, although the methods would likely be controversial (more hunting with dogs, hunting year-round, targeting younger animals, etc.). And in urban areas, hunting can be a tricky subject.

Some urban jurisdictions have started culls, including here in DC. Rock Creek Park started a deer cull a few years ago, hunting dozens of deer every year in an effort to reduce the deer population to about 15-20 deer per square mile (in 2013, there were 77 deer per square mile. If you go back a few decades, deer sightings were so rare in the park that NPS kept records of deer sightings by the public! Hard to believe now). Professional sharpshooters are employed, and the venison is donated to local food pantries. The park uses an adaptive management approach, meaning that they do regular deer surveys and adjust their target numbers each year based on the results. Needless to say, this has been a less than popular program in some quarters. Contraception is an alternative, but can still be quite expensive (the NPS plan for Rock Creek doesn’t preclude the use of contraceptives eventually) and can have mixed results, so maybe that isn’t a perfect solution either.

Urban deer management poses challenging ethical questions, but at the end of the day something does need to be done. When you walk through much of the park, there’s a very obvious browse line — up to where deer can reach, there are very few plants left. This hurts the animals that need that understory, whether for shelter or food (or both). It also hurts the forest itself, as there’s little to no tree regeneration in some parts of the park.

There are no easy answers here, to be sure. Throw in people’s concerns over deer eating their gardens and deer-human car accidents, and, well, it makes me glad that I studied coyote-human conflict in grad school instead of deer-human conflict — coyotes were tough enough!

Cromsigt, Joris P.G.M., Kuijper, Dried P.J., Adam, Marius, Beschta, Robert L., Churski, Marcin, Eycott, Amy, Kerley, Graham I.H., Mysterud, Atle, Schmidt, Krzysztof, and West, Kate. 2013. Hunting for fear: Innovating management of humna-wildlife conflicts. Journal of Applied Ecology, 50: 544-549

Laundré, John W., Hernández, Lucina, and Altendorf, Kelly B. 2001. Wolves, elk, and bison; Reestablishing the “landscape of fear” in Yellowstone National Park, U.S.A. Canadian Journal of Zoology, 79: 1401-1409.