Non-lethal Deer Management Project in San Jose

A deer sterilization project starting in 2013 was approved by the California Department of Fish and Wildlife to control the deer population at a retirement community in San Jose.  Some does had ovariectomies while others had tubal ligations.  A cull using archers was the original plan, but with a large public outcry outside of the community and concerns about public safety, the sterilization project was approved.   Although the initial cost of the sterilization approach was higher than the use of archers, no follow up has been required going into 2021.  Culls using archers often require annual maintenance and can be difficult to execute given safety restrictions and deer learning to evade the archers.  Over time both approaches may cost about the same with large variations in cost related to factors such as the to the use of volunteers. 

It was expected that deer from outside the community would migrate in, so all does were sterilized, but no new deer migrated into the community.  The population fell below a target the community later set.  This project, supported by San Jose State University, started in 2016 with a goal of understanding why there was no migration of deer into the community using trail cameras to monitor the deer.  

As shown at right, openings were created in fencing to encourage migration of new deer into the area in an effort to restore some of the population.  Two fawns were later born from sterilized does, sterilization is not typically 100 percent effective, but one was a buck and one died at a young age.  Over the three years of this project, no does permanently entered the community but one doe spent some time near one of the openings in the fence.

This article by Hasan Z Rahim gives some history of the project.  This peer reviewed research paper also provides a summary and a deer population model. The paper describes a startling difference in the results at this site and a similar project done by Cornell University, where they reported a dramatic increase in the buck population.  As the data reported below show and as discussed in the research paper linked above, the buck population at this location fell dramatically.

Deer Count:  At the start of the sterilization project in January, 2013, the deer count was 175 with 105 does and 70 bucks, falling to 47 deer in spring, 2019, with 42 does and 5 bucks. Reporting stopped after Spring, 2019.  At this point there was a discussion about culling deer in the future.  

Spring, 2019 deer count (April):   42 does and about 5 bucks, 47 deer including a few does photographed (some on this page) after the count.  All of the sterilized does had been tagged, making them easy to count and making it easy to spot any untagged does that might have migrated into the community.

Fall, 2018 deer count:   56 inside the community, 50 does and about 6 bucks.  The count was done later than in 2017, during October when deer are in the rut (mating) and moving more often. 

Spring, 2018 deer count:   49 deer inside the community, 42 does and 6 or 7 bucks in April.  A few deer are spending time outside the count area.

Fall, 2017 deer count:   55 deer, 49 does and 6 bucks in August.  

Two Fawns Born

The trail camera photo below verified the reports of the first fawn seen in the area for years, pictured below her mother, Doe 100. See more on her page.  According to the records, Doe 100 had an ovariectomy at a very young age.  Doe 100 was found dead on September 10, 2016, no apparent cause. She seemed fatigued in the last video recorded. 
A test on one of the approximately 10 deer that died starting in September, 2016, came back positive for Blue Tongue, a hemorrhagic disease that is not infectious to humans or other deer, but is spread by insect bites. The video below shows the fawn nursing, clear evidence that this was her fawn.

Doe 100 Nursing Her New Fawn

Other does were seen keeping watch over the orphaned who was old enough to survive on his own.  The fawn was sighted two times during the deer count at the end of October and also on November 6, then throughout November.   The photo below of the fawn, showing the beginning of antlers, was taken at the end of November, 2016. 

A second fawn at the Villages:  During the summer of 2019 there were reports of a tagged doe with a fawn.  Photos from one resident confirmed that Doe 16, who had received an ovariectomy, was taking care of a fawn.  Speculation was that this was an orphaned fawn born outside the area.  Reports that Doe 16 had been seen nursing the fawn were confirmed by photos that the doe was lactating, demonstrating conclusively that she had given birth to the fawn.  The fawn died of unknown causes a few months later.  

Trail cameras were used to keep traffic of conditions and movement of these deer from summer 2016 to summer 2019.  Impressive antlers on this buck, photo taken in July, 2017.

Doe 11 likes to move around a lot.  She frequently moved in and outside the fenced area, showing that in-migration of local deer could easily happen. She is one of the does equipped with a radio collar allowing her movements to be tracked remotely.

Tagged Does Using Fence Opening Created to Encourage Migration of New Does into the Area to Increase the Population

The tagged does in the video above were all sterilized and are easy to visually distinguish from fertile, untagged does outside the fence.  This community is fenced except for a large open gate at the front entrance that also allows for deer to move in and out of the area.  After three years of no observations of new deer moving in the area, the community agreed to do a survey to find a good location for an opening to encourage deer migration into the community.  The video above shows the first opening that was designed to be high enough to prevent feral hogs from entering, but low enough that deer could jump in and out.   

Although deer were observed outside the opening, few deer ventured in.  One reason may be attributed the the "placeholder effect" where resident deer will discourage outside deer from entering their territory.  As shown in the video below, Doe 53 became the gatekeeper of the first opening, chasing untagged deer from outside the neighborhood back through the opening.

Doe 53 Chases an Untagged Doe Out of The Area

Given the lack of success at the first opening, a second opening was created at another location.  As with the first opening there were deer observed outside of the opening and some ventured in but none stayed.  The two videos below show first an untagged doe jumping in, then jumping back out only a few minutes later.  

Untagged Doe Jumps in at the Second Opening

Untagged Doe Jumps Right Back Out.

The number of deer seen outside declined over the three years that trail cameras were in operation.  Competition from feral hogs and dry weather were contributing factors.  At the beginning of the sterilization project, fences were reinforced eliminating openings that the deer had used to migrate into the areas which was much better habitat than outside. The video below shows three untagged does in a field outside the fenced area during the California winter.  In California, the dry summer is the most difficult time for deer to find food and water.

Three Untagged Does in a Field Outside the Fence

Although the fence openings were placed where no feral hogs were observed in the camera surveys used to select locations, the hogs appeared outside the second opening for a few weeks.  The fence design proved to be effective as while the hogs came right up to the opening, none were able to jump the fence.  See the video below.

Feral Hogs at Fence

As this picture of a buck in flight below shows, deer were able to use the opening to enter. The opening proved to be an effective hog filter.

Damage to landscaping was the reason the Villages gave to the California Department of Fish and Wildlife (CDFW) for their original proposal to cull the deer population.  The community contains a lot of well landscaped terrain and a golf course on the edge of dry foothills.  It was originally an important part of the deer habitat in the southeast of the Santa Clara Valley (Silicon Valley).   As part of the project, the CDFW allowed the community to make piles of clippings from the gardeners to draw deer away from the landscaping.  This approach has been used successfully and often to protect farm crops.  Below are a few examples of the deer making frequent use of the clipping piles which the community continued to pay for as part of their landscapping contract.  The first shows the fawn born to Doe 100 with some of the does in the community who took care of her when her mother died.

Fawn 100 Eating from a Clippings Pile with Does 51 and 43.

Does Eating from a Clippings Pile