Frequently Asked Questions

What is the Clifton Deer Program?

The Clifton Deer Program is a privately funded and volunteer led urban deer fertility control research study that has been operating in Cincinnati, Ohio since December 2015, in collaboration with the Cincinnati Parks.


The Program involves the surgical sterilization of female deer using a process called a “rapid ovariectomy.”  An ovariectomy is the removal of a female deer’s ovaries. The procedure is similar to, but less invasive than, typical spay surgeries used to sterilize domestic dogs and cats (because with ovariectomies, the uterus is not removed).

Where does the Clifton Deer Program operate?

We are located in the Cincinnati Neighborhood of Clifton.  We operate within a study area comprising the ~1 sq. mile area bounded by I-75 to the North and West, Clifton Ave. to the East, and Ludlow Ave. to the South. The study area includes three city parks (Mt. Storm, Rawson Woods, and Edgewood Grove) and the surrounding residential neighborhood. 


Under what authority does the Clifton Deer Program operate?

The Clifton Deer Program operates under a scientific research permit issued by the Ohio Department of Natural Resources, Division of Wildlife, in 2015 and renewed in 2018, 2020, and 2023.  The research permit is held by White Buffalo, Inc., the Program’s professional consultant.  The current renewal is effective through Spring 2026.    


The Program was approved by the Cincinnati Board of Parks Commissioners and by the Clifton Town Meeting Board of Trustees in 2015. 

Why is the Clifton Deer Program structured as a research program?

In Ohio, wild animals (including white-tailed deer) are considered the property of the state.  Handling or “capturing” a wild animal in any way – even if the intent is not to harm and the animal will be released – generally requires a permit from the Ohio Department of Natural Resources, Division of Wildlife (ODNR). 


Currently, the only type of permit available for fertility control programs is a scientific research permit.  To obtain a scientific research permit, a fertility control program must be designed to explore questions of legitimate scientific interest, must collect and analyze data to answer those research questions, and must submit detailed, annual reports tracking its progress to the ODNR. 


Lethal programs are allowed to occur under “management” permits and as such are not subject to the same requirements. 

What are the Clifton Deer Program's research objectives?

The primary research objective of the Clifton Deer Program is to assess the cost, feasibility, and population impacts of a white-tailed deer capture and sterilization project in a densely developed suburban community. Ultimately, the goal is to determine the lowest deer density that can be achieved with only non-lethal management techniques given potential immigration effects.


A secondary objective is to assess the feasibility of training local volunteers to capture, handle, and surgically sterilize female white-tailed deer to determine how well this concept can be scaled up and sustained with minimal use of outside consultants.

What is the process for darting, sterilizing and releasing deer?

Our field operations typically occur in late Autumn/early Winter over several weekends.  We work mostly at night when deer are most active and people are not.


Trained capture specialists locate and dart female deer from vehicles on public roadways and at bait stations on volunteer properties within the study area. The deer are tracked until they are unconscious (typically just a few minutes), and then transported to a surgical site where a veterinarian performs ovariectomies and administers long-acting antibiotics and pain relievers. All sterilized deer are fitted with state mandated, numbered, ear tags. Treated deer are then returned to a safe location close to the area where they were found and monitored until recovered. The entire process, from initial darting to release, takes approximately 2 hours per deer.


The team coordinates its activities as appropriate with local law enforcement.

What is the science behind the Clifton Deer Program? How does sterilization lower the deer population?

To reduce the size of any deer herd, mortality plus emigration (sometimes called dispersal) must exceed births plus immigration.


Lethal programs try to achieve a reduction by increasing mortality. Nonlethal programs like this one try to achieve a reduction by reducing births.


We use a procedure called a rapid ovariectomy to tackle the birth side of the equation. It is similar to the procedure your vet may have used to spay your dog or cat, but less invasive because an ovariectomy just removes the ovaries, not the uterus.  A doe without ovaries no longer experiences estrus and can’t become pregnant.


By performing ovariectomies on a very high number of the does within a herd – 95% or higher – births can be cut to near zero.   


The bottom line is that low migration (the tendency of most deer to stay close to home, discussed here) coupled with very few births makes it possible to gradually reduce the population through normal attrition as the herd ages.

In an open environment, don't deer just come and go?

Research shows, and our experience confirms*, that urban/suburban female deer have very high “site fidelity” – most spend their entire lives within roughly 1 square mile of where they were born.  Further, they have high family fidelity – most live in distinct matriarchal or social groups.


While the behavior of males is different, with most males leaving their herd of origin by age 1 or 2 (perhaps as an evolutionary adaption against inbreeding), site fidelity among males over the age of three is moderately high as well.


There are certainly exceptions, and environmental factors can temporarily or permanently displace deer. But most adult deer, especially the females, settle in one neighborhood, even in an “open” or non-insular study area, with no walls or fences to prevent deer from coming and going.


The tendency of most female deer to stay close to home means that migration rates (existing female deer moving out of the study area, and new female deer taking up residence in the area) are low.  Low migration makes it possible to achieve and maintain a sterilization rate of over 95% within the study area, which in turn means that very few fawns are added to the herd.  This allows the herd to shrink through normal attrition over time. 


*From the wealth of data we’ve collected over an extended period of time, we know that the deer behavior documented by researchers applies in Clifton – no matter what time of year we look, we see the same individuals and the same family groups in roughly the same areas of the study area. We’re also able to identify behavioral outliers at an individual level – for example, the occasional young buck who is still with his birth family long after most bucks would leave, or the occasional adult female with wanderlust.

Is the procedure humane? What is the capture and handling mortality rate?

Surgical sterilization is routinely used to control population growth of domestic animals (i.e., dogs and cats) and has also been used in at least 14 other species. It is recognized as safe and humane for use in deer by The Humane Society of the United States when management action is justified. 


In a 2021 peer reviewed paper, White Buffalo, Inc. reported in 2021 that of 570 deer handled (including 493 surgical sterilization procedures), there was a total of 15 capture and handling related mortalities, with 4 individuals euthanized prior to surgery due to capture related injuries (0.7%) and 11 post-surgical mortalities (2.2%).  The reported results included those of the Clifton Deer Program and five other study sites around the country. 


Between 2015 and 2023, the Clifton Deer Program has experienced three capture and handling related mortalities (3.0%).   

Why are you sterilizing female deer and not males?

Urban female deer typically spend their entire lives in matriarchal herds in a small (1 square mile or less) range. The home range for male deer tends to be larger, they tend to travel  more and have higher levels of migration (particularly younger males, and particularly during rutting season), and they will breed as much and as often as the opportunity presents itself. Because a single unsterilized male can impregnate many female deer, there is less of an advantage to sterilizing males in open urban environments.

Why are sterilizations only done in Fall or Winter?

There are several reasons: (1) Deer can be more easily lured to bait stations and captured when foliage, their normal food source, is scarce; (2) they are more easily tracked when visual obstruction from foliage is minimal; and (3) sterilizations done after March 1st, , when female deer are typically entering the late stages of pregnancy, are more complicated as the surgeon must work around an enlarged uterus, increasing risks to maternal and fetal health. Further, pregnant deer give birth typically between April and July, and may still be nursing as late as September.


Taking these factors together, the optimal time for sterilization is between October and Mid-February.

Are deer put at risk by having surgery in cold weather?

No. Unlike the situation with small animals (such as feral cats), deer are biologically adapted to living outside in winter. Veterinarians who have performed the procedure have advised us that deer are not harmed by post-surgical release into cold weather conditions.

What is the impact of sterilization on the fetus of a pregnant doe?

It depends upon the stage of pregnancy. The gestation period of a female deer is typically between 190 and 210 days (a little less than 7 months). Most deer will become pregnant in November or December and will give birth between the months of April and July.


Up to approximately the 120th day of pregnancy (the 4th month), the ovaries are necessary to sustain a deer’s pregnancy, so sterilization will result in miscarriage. The fetus at this stage of pregnancy is still extremely small (likely less than 1 lb.), and there is no evidence that deer experiencing miscarriages under these circumstances are harmed.


After approximately the 120th day of pregnancy, the ovaries are not necessary to sustain pregnancy. A deer sterilized after the 120th day of pregnancy can be expected to give birth to the fawn(s) she is carrying in the Spring, but will thereafter be infertile.

How do ovariectomies differ from tubal ligations? Will tubal ligations ever be used?

Ovariectomies involve the removal of the ovaries; the deer becomes infertile and will never experience estrus (i.e., go into heat) again. Tubal ligations involve the tying of the deer’s fallopian tubes to prevent implantation of a fertilized egg in the uterine lining. Deer with tubal ligations continue to experience estrus, and because they do not become pregnant after breeding, they may continue to cycle for up to 5 months. Having a large number of female deer repeatedly going into heat over a multiple month period has been associated in one field study with an increase in the number of bucks drawn to the study area; even though the population of female deer and fawns declines with tubal ligation, the overall population may not be reduced (at least during the breeding season) because of the influx of bucks.


To date, tubal ligations have not been used in the Clifton Deer Program.  They will only be used in the unlikely event a deer is found to be in late state gestation and switching to a tubal ligation is deemed by the veterinarian to be necessary to protect maternal or fetal health.  

What are your results so far?

We measure our success both in terms of effectiveness (do we have demonstrable, sustained reductions in the deer population over time?) and cost-effectiveness (is the program sustainable from a cost perspective?).  Our results to date can be found here.

How do you measure changes in the deer population? Are your numbers credible?

When accuracy and reliability are important, as in a long-term scientific study like the Clifton Deer Program, methodology matters.  The quality and quantity of data collected and analyzed matter, too, as does the consistency of results over time. By these metrics, the Clifton Deer Program’s reported results are highly reliable.


In addition to White Buffalo’s annual population surveys discussed below, we monitor the Clifton study area herd extensively throughout the year, typically through field camera data collected and analyzed periodically throughout the Summer, Fall, and Winter at up to nine sites (so that the entire 1/sq. mi study area is covered).  We use color photo white flash trail cameras to obtain high quality photos at night as well as during the day. We’ve collected and analyzed over 50,000 photos of deer in the study area since December 2015. As explained below, we can, quite literally, count the deer in a “census” fashion.


So how can we literally count the deer?


Virtually every female deer in the Clifton study area has been tagged and is therefore individually identifiable. More than 25% of tagged deer were also radio collared, allowing us to periodically confirm their locations and, with mortality sensors, their status, for several years after release.


The back of each tag bears White Buffalo’s telephone number, so tagged deer who die in deer-vehicle collisions or who are otherwise found deceased are reported to White Buffalo.


We also identify each tagged deer’s family or social group and track it over time.  


Finally, mature males are individually identified based on their unique antler patterns.


By being able to individually identify a very high percentage of the deer in a given area and then follow those individuals over time, we are able to obtain very credible data not only about the population at a macro level, but about mortality, immigration, dispersal, and fawn recruitment at a micro level – essentially allowing a census of the deer to be taken every year. That is exactly what we are doing in Clifton.


White Buffalo performs annual population surveys (eight through Feb. 2023, including the “baseline” survey conducted in December 2015) using two to three established estimation methods in addition to the “census” method. Even though each method takes a different approach, the results of each are similar (increasingly, virtually identical), suggesting a very low margin of error. White Buffalo reports details of its methodologies, analyses, and conclusions to the Ohio Department of Natural Resources and the Cincinnati Parks annually.


In 2021, White Buffalo published Clifton’s results along with those of five other sterilization sites around the nation in a peer reviewed article in a scientific journal. The article concluded that “significant reductions in local deer densities using high-percentage, surgical sterilization programs can be achieved in non-insular locations.”

Why did you choose sterilization over immunocontraception?

While both methods can be viable alternatives to lethal population control in certain circumstances, sterilization is the only option at present that is 100% effective and that does not require repeated treatments. Researchers are working on advancements in contraceptive agents and delivery technology that may make immunocontraceptives a better option in the future. Until then, an in-depth comparison of available methods led us to determine that  sterilization offers the most practical and most cost effective method of fertility control for Clifton.


At this time, non-lethal alternatives to bow-hunting or sharpshooting are practically limited to sterilization and immunocontraception. There are two chemical contraception options available: GonaCon and Porcine Zona Pellucida (PZP).




GonaCon (including a formulation known as “GonaCon-Blue”) is a gonadotropin-releasing hormone (GnRH) immunocontraceptive vaccine that stimulates the production of antibodies that bind to GnRH, a hormone that signals the production of sex hormones (such as estrogen and progesterone).  By binding to GnRH, the antibodies reduce GnRH’s ability to stimulate the release of these sex hormones. As a result, mating activity is reduced and a deer receiving GonaCon will be infertile for as long as a sufficient level of antibody activity is present. GonaCon has been registered with the EPA for use in white tailed deer 1 year of age or older. Currently, a single shot of GonaCon is highly effective in the first year, and in some deer antibody levels remain high enough to prevent pregnancy for up to 5 years. However, antibody levels fall off more quickly in other deer, such that 20% to 50% of treated deer regain their fertility between treatments. The efficacy rates tend to be higher in controlled studies (e.g., with captive deer) than in typical field conditions.


GonaCon currently is only EPA registered for hand injection each time it is given (rather than being registered for remote darting). This means that a deer who is first treated with GonaCon at age 1 will likely need to be captured, sedated, and vaccinated at least twice in her lifetime, and may still give birth to multiple fawns. Scientists are working to develop improvements to  GonaCon™, including possible oral or remote darting delivery methods. These improvements are not yet available and their timing is uncertain.


Porcine Zona Pellucida (PZP)


PZP is a naturally occurring protein found in pig eggs. When the PZP vaccine is injected into the muscle of a female deer, it stimulates her immune system to produce antibodies against the vaccine. These antibodies block fertilization, but unlike GonaCon, do not suppress the stimulation of sex hormones, so deer receiving PZP continue to experience estrus. In fact, PZP appears to extend by approximately 2 months the estrus cycles of treated deer who do not become pregnant. There is no evidence this harms the treated deer, though it does extend the mating season and may increase undesirable mating behavior such as chasing.


“Native PZP” (delivered as two injections several weeks apart, for one year of contraception) has been registered with the EPA as “Zonastat-H” for use in horses, with the sub-label “Zonastat-D” for use in white tailed deer.  As of the time of this writing, Zonastat-D is also registered at the state-level EPA in South Carolina.  A newer formulation known as “PZP 22” (delivered as one injection, for 22 months of contraception) has not yet been registered with the EPA for use in white tailed deer, but use has been permitted in research studies.


The most researched formulations of PZP have been found to be highly effective when given twice in the first year (the vaccine and a subsequent booster) and annually thereafter. PZP 22 does not require a first year booster and can last up to 2.5 years.  Additionally, treatments after the first one can be delivered remotely by dart.  Efficacy rates of PZP 22 in deer appear to range from ~90% to 96% in Year 1 and ~76% to 80% in Year 2 (meaning that ~4% to 10% of treated deer may continue to fawn in the first year after treatment, and ~20% to 24% of treated deer may continue to fawn in the second year after treatment).


Because suburban deer can be long-lived, a deer who is first treated with PZP at age 1 may need to be treated 3 to 4 times in her lifetime.


As with GonaCon, scientists are working to develop improvements to PZP (to increase the length of time needed between treatments, as well as its efficacy) and current delivery technology. These improvements could make contraception using PZP a much more desirable option, but they are not yet available and their timing is uncertain.


Advantages of Sterilization over Immunocontraceptives Today


We believe sterilization remains at this time the best choice because:


  • Sterilization is 100% effective over the lifetime of the deer. The effectiveness of multi-year immunocontraceptives declines over time. Any non-lethal program will only be successful in reducing the deer population if natural attrition through death and emigration exceeds natural increases through births and immigration. Even a 10% “break through rate” (deer who become pregnant between treatments) can be enough to offset natural attrition.


  • Sterilization requires only one treatment over the lifetime of the deer. Immunocontraceptives require multiple treatments.


  • It is less expensive to sterilize each deer once than to vaccinate every deer multiple times.


  • Deer subject to repeated darting tend to become “educated,” making them less approachable and less easily lured to bait. Locating and successfully revaccinating previously treated deer becomes more challenging and labor intensive over time. This does not happen with sterilization.


  • A deer who is sterilized and emigrates out of the study area will remain infertile and will not contribute to fawning in her new area. A vaccinated deer who leaves the study area (or who can’t be located or darted when it is time for her revaccination) will become fertile again.


  • If at any point the ODNR stops issuing renewal permits or the Clifton Deer Program ceases to operate, sterilized deer will remain sterilized. The investment will not be lost. Deer who have been vaccinated will become fertile again, and the investment in contraceptives will be lost.


  • Deer who have received ovariectomies do not experience estrus, so bucks are not attracted to the area during mating season (adding to the deer population) and undesirable “chasing” and other breeding activity do not occur.


  • If contraception becomes a better choice in the future, there will be no loss or impediments to switching methods that are used on immigrant deer.
Will Clifton eventually run out of deer?

In an open urban environment like Clifton, there will always be some unsterilized deer migrating into the area.  In the event that the Parks’ population goals are exceeded and the community wants more deer, it will be possible to leave some immigrant deer unsterilized so the population can grow.

Why spend time and money preserving deer that could provide meat for food pantries?

The Ohio Division of Wildlife estimates there are 700,000 deer in Ohio, with 210,977 killed by hunters in 2022-2023 alone.  Of the many social and political factors that contribute to human hunger, we see no evidence that a shortage of deer generally, or the protection of our nearly tame small urban deer herd, is one of them.


Every charitable or philanthropic organization speaks for the interests and values of its founders and supporters in addressing social needs it believes are important.  Clifton Deer is no different as it calls for the holistic health of the community, which includes preserving deer as part of a healthy ecosystem. We see no contradiction between a commitment to preventing unnecessary suffering and death of animals and a commitment (shared by us and many of our supporters) to relieve human suffering. 

How much does a sterilization program cost?

Many variables contribute to the cost of a sterilization program, so costs will be community-specific.  The size of your study area, the number of deer in your herd, and your ability to train local volunteers to gradually assume key roles (including darters and surgeons), among other considerations, all factor into both initial and long-term costs. 


We caution against using a “per deer” cost framework.  In our experience, overall program costs (especially with the training of skilled volunteers) decrease over time, even as the “per deer” cost rises.  Two factors account for this:


  1. Some program costs are fixed regardless of the number of deer sterilized.

  2. As the percentage of tagged does rises, finding and capturing the few remaining untagged does (typically, the most wary and elusive ones) becomes more labor intensive; it is the problem of finding a needle in a haystack.  Where once every doe a darter saw would be a good target, in later years there might be only one, and she might be in a crowd and not in a position to allow darting.  Additionally, after several years of operations, many of the does are “educated” and more alert to the possible presence of a darter as they approach a bait site, decreasing the number and frequency of darting opportunities.


Our costs to date are located on our Results page. 

Is sterilization cost effective?

Implied in the question is another: “compared to what?”  


When lethal means are deemed necessary, many communities rely on volunteer bow hunting programs.


Unfortunately, it is very difficult to compare the cost effectiveness of such programs to sterlization programs. 


First, rarely or never are the exacting measurements of populations and population changes used by the Clifton Deer Program (made possible by the fact that we can individually identify virtually every member of our herd) applied to volunteer bow hunting programs.  The methods that are used (such as aerial infrared counts), while the best available in unmarked herds, typically result in highly variable approximations at best.  The number of deer “harvested” each year, while often the focus of reporting, says little if anything about whether the herd size is actually being reduced.  Without a quality and uniform standard of measurement, comparing the effectiveness of volunteer bow hunting to the effectiveness of sterilization is impossible.


Likewise, costs of bow hunting are rarely measured as comprehensively as those in the Clifton Deer Program’s precisely documented financial reporting, where our expenses are part of the research and where every dollar is privately raised and accounted for. True and ongoing cost comparisons would have to include hunters’ personal expenses for equipment and supplies as well as the sponsoring institution’s dedication of employee and administrative time and expense to overseeing the bow hunting program.


No deer management program, lethal or non-lethal, can succeed as a one-and-done operation.  Only ongoing, sustained effort can manage effectively the problem of ecologically destructive overabundant herds. While the learning curve and start-up costs for sterilization might look relatively high, a true cost effectiveness comparison requires examination of long term costs and effectiveness of each method at achieving and
maintaining an environmentally acceptable population level.

Will a sterilization program work in my community?

From a technical standpoint, a sterilization program is most likely to be effective in a suburban or urban area with a dense network of roads and at least some “soft” boundaries such as highways or large bodies of water.  We suggest that you consult early with an expert like White Buffalo, Inc. to determine suitability of the intended area.


Even if a sterilization program would work in your community from a technical standpoint, political will, solid program leadership, and funding are necessary to launch and sustain a program. 


Exploring the idea of a deer sterilization program can feel daunting … we know, we’ve been there! While every situation is different, we hope the general thoughts offered here, based on our experience, may help you frame discussions, assess resources, and anticipate challenges.