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Fertility Control 

The Deer population is affected by four factors; birth rate, death rate, immigration rate and emigration rate.  Because relocation is not a viable option (due to concerns about mortality rates, new immigration of deer from outer areas and the lack of land availability for relocation), if we wish to reduce the population of deer we must either increase the death rate or decrease the birth rate. Both require long-term commitment and significant expenditure of tax dollars. 


Population control techniques are generally implemented only when an area has exceeded “biological carrying capacity."   Biological carrying capacity is based on herd health, population counts, and objective data related to browsing damage and biodiversity impact.  To date, Ann Arbor has no objective evidence of exceeding biological carrying capacity.  Instead, we are challenged by, as the DNR noted, “cultural carrying capacity," where some residents consider the deer a nuisance and have raised other concerns that can be associated with urban deer.  We do, however, believe fertility control methods are an effective and preferred method over indiscriminate and controversial killing of healthy animals.










Fertility control for animals is not as crazy as it sounds.  For one, animal sterilization was developed in the 1800s and has been common since the 1960s, becoming standard practice by the 1980s.  Spaying/neutering is now considered the only proven method for reducing the companion animal population, is legally required in animal shelters in most states, and is responsible for the reduction of euthanasia for dogs and cats from about 23 million in the 1970s to about 4 million today.  In fact, HSHV euthanized ~25,000 animals annually in the 70s, but today, following an effective no-kill strategy, only puts down those who are critically ill or wounded, or dangerously aggressive. 


Fertility control has also been successfully used with feral/outdoor living cats. After using a "catch and kill" method for decades, shelters and animal welfare groups tired of senseless and never-ending killing of healthy animals.  "Trap-Neuter-Return" or "TNR" was developed, using sterilization for effective and humane population control.  This humane fertilization control has been shown to decrease the size of cat colonies over time


We have also increasingly turned to fertility control methods for wild animals in places around the country and world.  Often, conservation efforts revolve around protecting and increasing a threatened species. (You might be surprised to learn that White-tailed Deer were nearly extinct and were part of restoration efforts.)  But when a species succeeds beyond human tolerance in places people don’t want to shoot for ethical and/or safety reasons, fertility control methods have been successfully implemented. Feral dogs and stray dogs, elk, wild horses, Canada geese, and deer have all been a part of surgical sterilization or immunocontraception projects.  



While fertility control techniques may not create the immediate drop in population that culling does, it does offers stabilization and a moderately steady decline.  These humane strategies also prevent the unintended consequences of a cull, such as increased birth rates and the migration of new animals that may introduce new diseases to the area.  Stopping fertility also reduces the extra food requirements of pregnant doe, helping reduce concerns about landscape damage and over-browsing in green spaces. 


Sterilization:  Deer sterilization has been tried in many communities and is effective in reducing population over time.  The cost is about $350-$1000 per deer depending on the amount of donated goods and services involved.  (A Michigan large scale spay/neuter organization has already expressed interest in helping support a possible project.)  Sterilization generally involves darting doe with a tranquilizer, and doing an ovarianectomy (a safe and less invasive sterilization procedure that involves the removal of the ovaries that makes the deer permanently infertile and unable to go into estrus).  The technique takes about 20 minutes and each animal is tagged, administered a drug to reverse the tranquilizer and is set free.  

Listen to biologist Rick Page who says fertility control is a more cost-effective option than culling for reducing deer populations


We also have two good options for Immunocontraceptives:


  • Gonacon:  An EPA approved vaccine/immunocontraceptive that blocks the hormones needed for reproduction.  It safe and considered effective for up to five years and has also been used on bison, elk, swine, feral cats and feral dogs.  Cost for administration is about $500 per deer.  Deer are generally anesthetized by dart, administered the vaccine and tagged for identification  A project using Gonacon would require special approval from the MDNR.


  • PZP:  Is also a safe vaccine/immunocontraceptive that effectively prevents pregnancy and helps stabilize and reduce the population over time. PZP currently has approval for use with wild horses and burros, but research projects may also be approved with federal and state regulatory bodies.  Deer are generally anesthetized by dart, administered the vaccine and tagged for identification. Cost is about $500-1000 per deer, which would wear off after 2-3 years. Read about 2 long-term studies with PZP that showed significant reductions in the deer populations.


The Humane Society of the United States and the Humane Society of Huron Valley have both stated a willingness to provide resource assistance to reduce project costs if the City of Ann Arbor should decide on a non-lethal approach. See the HSUS presentation to Ann Arbor City Council here, and the HSUS site assessment and statement of interest in working with Ann Arbor here.

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