Cornell University scientists accidentally create ‘buck magnets’ in effort to control deer population

Nick Canedo on October 16, 2014 at 2:39 PM, updated October 16, 2014 at 4:47 PM

Cornell University launched a program in 2009 aimed at satisfying all Ithaca residents by controlling the area’s deer population in an innovative way. Fast forward to 2013, and scientists were left puzzled: deer pregnancy rate was down, but the population remained the same.

How did this happen? Turned out the scientists had unknowingly created “buck magnets.” The Washington Post recently chronicled the university’s program that led to this surprising result.

An abundance of deer in urban and rural areas has been perceived as a problem by many in Central New York. There’s nearly 220 deer living within the east side of Syracuse and an adjacent part of the town of Dewitt, according to an April 2014 State University of New York College of Environmental Science and Forestry study. Community members have debated how to solve the problem, with some promoting culling the deer heard while others suggest non-lethal injections.

In 2009, Ithaca residents and the Cornell University community had reached their boiling point of dealing with the influx of white-tailed deer that ate gardens, spread Lyme disease and risked human lives with car collisions, the Post reports. Cornell sought a solution that would satisfy everyone, including animal rights activists.

Instead of dealing with the deer population with the usual hunting, Cornell administrators chose to launch a five-year pilot program that combined doe sterilization and hunting to manage the population. Without natural predators, deer reproduce until their numbers were limited only by the availability of food, the Post reports.

“The method of contraception chosen by Cornell was tubal ligation, in which a doe’s fallopian tubes are either blocked or severed. This prevents egg cells from reaching the uterus. Unlike chemical forms of birth control, tubal ligation is typically permanent and avoids the expense of capturing the same deer each year to maintain their infertility. At a cost of roughly $1,200 per deer, 77 does were captured and sterilized though tubal ligation. (Without the help of the Cornell University College of Veterinary Medicine, the costs would have been higher.)”

The program worked in one category: the birth rate went down. But over the course of the five-year program, the total number of deer stayed the same. While the sterilization decreased fawn and doe numbers, an increase in the buck population offset the population change. By 2013, around 100 deer lived on campus–the same amount as when the program started.

Scientists discovered that their program accidently created “buck magnets” by preventing doe pregnancy.

“Under normal conditions, all female whitetails go into heat within several weeks of each other and become pregnant at around the same time. This annual event is called the rut. However, if a doe is not impregnated during the rut, it will enter heat again the following month and again the month after that. Because the ligated does were unable to become pregnant, they continued to produce chemical signals of readiness to reproduce — signals that can attract bucks from miles away.”

The result should’ve been expected, Bernd Blossey, chair of the Cornell Deer Research and Management Committee, told The Post. “I’m an ecologist looking at the literature,” he said. “I thought that sterilization in an open population where things can move in and out won’t work. Maybe it was worth doing it in a sophisticated way to say we tried in the best possible way and it didn’t make a difference.”

After assessing the data, Cornell’s administration discontinued the tubal ligation program and switched to using professional trapping and hunting by volunteer archers to control the deer population. Paul Curtis, an associate professor and extension wildlife specialist at Cornell, told the Post that the school’s camera survey showed 100 to 105 deer on campus in winter 2013. After the Cornell switched tactics, the camera survey estimated 58 deer remained on campus in 2014.

Curtis’ team has begun experimenting with ovary removal in deer, but, once again, the team has a surprising result. Scientists surgically removed the ovaries from three deer, but one of them still became pregnant again.

Though the scientist suspect that some ovarian tissue may have escaped the scalpel and regrown into a functioning ovary, it remains unclear how the pregnancy was possible.

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