Thursday, November 21, 2019

Ten-Year Deer Management Study at Cornell University, Ithaca, NY

The Cornell Deer Management Study efforts are now complete and published in the peer-reviewed literature. The findings are quite interesting. You can view a Video Abstract on Vimeo. The full research paper entitled, Red oak seedlings as indicators of deer browse pressure: Gauging the outcome of different white‐tailed deer management approaches, is open access and can be viewed here. Provided below are the highlights of their findings.

Different deer management zones were established around the Cornell Campus including a deer fertility control area, a recreational hunting area, and a “control” area where no deer management occurred. The researchers individually marked more than 100 deer. This allowed them to use annual camera surveys to assess the population, using mark - recapture models. They also used planted red oak seedlings to assess ecological outcomes. The combination of knowing the herd size while measuring ecological outcomes is unique, no other study has done this in open populations.

1. Fertility control: despite a 90%+ sterilization rate, it did nothing to reduce the deer population, this was not surprising.
2. Recreational hunting: as presently implemented by agencies and executed by hunters, also did not control the deer population. This may come as a surprise to some, researchers allowed access to all lands available and killed hundreds of deer, still to no avail.
3. Using planted red oak seedling sentinels as indicators of ecological outcomes, the study showed basically no difference in the fate of oak seedlings between the sterilization, recreational hunting, and no management zones, with slight annual variations. Other oak mortality factors, rodents etc., barely registered. Deer herbivory was rapid in late spring and summer.
4. Halfway through the study the researchers switched to the nuisance permits and eliminated recreational hunting in a core area surrounding the campus. Only then were they able to drop the deer population substantially. With the drop in the deer population, deer browse rate declined linearly. This showed how powerful the red oak sentinel method can be as it tracks changes in the deer population. However, immigration of deer from the surrounding areas more than offset deer kills, even with hunting over bait and at night, researchers were unable to get the oak seedling browse rates below 20%, not low enough to allow for successful forest regeneration. 
5. The deer nuisance permit approach provided benefits but researchers are not sure it will provide the lasting deer reductions required to deliver the ecological and human health benefits, i.e. highly palatable plants and Lyme disease, needed for a healthier future. Ultimately, we need to fundamentally re-think and revise how we manage deer and landscapes. Those advocating for no deer kills in the animal rights community will likely not care for these results. Researchers also expect that many hunters, who are now accustomed to seeing large numbers of deer, or folks in state wildlife agencies may be surprised. For too long we simply believed that recreational hunting will deliver benefits if access is provided without seeing data showing that these assumptions were in fact true. 

The complaints by foresters and conservationists about the erosion of biodiversity assets have sounded loud and clear starting with Leopold some 80 years ago. It is time that we take our social and ecological responsibilities seriously and manage deer in ways that allows for a future that includes forest regeneration without fences, a walk in the woods without dousing us, our kids and our pets with tick repellent, and forests and landscapes to teem with the beauty and biodiversity that is still possible.  Denuded forests that also will not allow for thriving deer populations are the worst of all possible outcomes, unfortunately we are well on our way to that. We hope that our work, the current paper, and others that will follow will help chart a way to a better future. Will regulated market hunting and allowing the return of big predators, wolves and mountain lions, be essential to achieving this?

Dr. Bernd Blossey
Associate Professor
Department of Natural Resources
206 Fernow Hall, Cornell University

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