Frequently Asked Questions About Surgical Sterilization

What is an ovariectomy?

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

Is the procedure humane? What is the surgical mortality rate?

Why are you sterilizing female deer and not males?

Why are sterilizations only done in Fall or Winter?

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

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

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

Why choose sterilization over immunocontraception?

Which is more invasive – immunocontraception or sterilization? 

Will we eventually run out of deer?

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

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What is an 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. Using the “rapid ovariectomy” technique developed by Dr. Steven Timm, DVM, and the White Buffalo team, preparation and surgery take place in the field and typically take 20 minutes or less. Back to top

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

The capture and sterilization team works at night when deer are most active and  people are not.

Wildlife professionals dart female deer with tranquilizers at bait stations and private drives (where volunteered), and from vehicles on public roadways within the study area. The deer are tracked until they are unconscious. A recovery team recovers and transports the doe to a temporary surgical sterilization site.  A licensed and trained veterinarian then performs the ovariectomy and gives the deer injections of long-acting antibiotics and pain medication.

All sterilized deer are fitted with numbered ear tags, and selected mature does are radio-collared to facilitate future capture efforts, track migration rates and patterns, and assess survival rates. Data regarding size, age and condition is also collected.

Treated deer are then returned to the area where they were captured (in locations with the lowest likelihood of human disturbance during recovery), administered a reversal agent, and are monitored for complications with recovery.

The entire process, from initial darting to release, takes approximately 1 to 2 hours per deer.

The team coordinates its activities as appropriate with local law enforcement  Back to top

Is the procedure humane? What is the surgical 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 species. It is recognized as safe and humane for use in deer by The Humane Society of the United States. The surgical mortality rate, as reported by The Humane Society of the United States and in White Buffalo studies, is less than 1% (although mortalities related to the capture itself,  as, for example, in the case of capture myopathy, can sometimes occur).  Sterilized deer appear to be healthier and calmer than fertile deer because they don’t experience the physical stresses of being chased by bucks during mating season and of pregnancy, birth and nursing. Back to top

Why are you sterilizing female deer and not males?

buckUrban 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 (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 as many female deer, across multiple herds, as several unsterilized males, there is little advantage to sterilizing males in open urban environments unless every single male over a large geographic area can be located, captured and sterilized. Back to top

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 the forest canopy cover provides minimal visual obstruction; 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. Back to top

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 in the field have determined that deer are not harmed by post-surgical release into cold weather conditions. Back to top

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 150th day of pregnancy (the 5th month), the ovaries are necessary to sustain a deer’s pregnancy, so sterilization will 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 150th day of pregnancy, the ovaries are not necessary to sustain pregnancy. A deer sterilized after the 150th day of pregnancy can be expected to give birth to the fawn(s) she is carrying in the Spring, but will thereafter be infertile. Back to top

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.

It is White Buffalo’s practice to only do tubal ligations when a deer is found to be in late state gestation and switching to a tubal ligation is necessary to protect maternal or fetal health. Because White Buffalo does not perform sterilizations after March 1st, these occurrences are quite rare. Out of over 500 sterilizations performed by White Buffalo since 2009, tubal ligations have only been necessary in 22 cases (about 4.4% of the time). Back to top

Why choose sterilization over immunocontraception?

While both methods are viable alternatives to lethal population control, 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 the better choice in the future. Until then, in an open urban environment like Clifton, we determined that sterilization offers the most practical and most cost effective method of fertility control. Back to top

Which is more invasive – immunocontraception or sterilization?

It depends on how one defines “invasive.” Sterilization involves a 20 minute surgery, but only occurs once in the deer’s lifetime and does not involve chemically altering the deer’s reproductive processes. Immunocontraceptives do not involve surgery, but do require repeated darting of the deer throughout their lifetimes with contraceptives that chemically alter their reproductive processes. Back to top

Will we eventually run out of deer?

In an open urban environment like Clifton, there will always be some unsterilized deer migrating into the area.   Once population goals are reached,  a decision will be made as to whether migrating deer need to be sterilized in order to maintain a healthy population level with neither too many -or too few – deer. Back to top

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

People with different sensibilities about animals can view this project differently.  Some think the deer were here first, that the problems with deer are caused by humans, and that people should adjust themselves to the deer’s presence and leave them alone.  Others view deer simply as pests and opportunities for sport hunting and food.  CliftonDeer.org takes a path somewhere in between.  It respects the Parks goal of protecting our complex and threatened eco-systems, which include the deer, and accepts the research showing that bow-hunting alone cannot achieve eco-sustainable deer population levels.

As with programs for the arts and other philanthropic ventures, CliftonDeer.org seeks to contribute to the holistic health of the community, in this case by preventing the unnecessary suffering and sometimes terrifying death of deer in our small urban parks.  It is heartening to know that so many folks are committed to improving the quality of life for our whole community. Choosing one path does not need to mean the demise of another. We can choose both.  Back to top

An exciting, innovative, and humane deer fertility control pilot program