Villages, San Jose, Update on Progress of Deer Sterilization Program November 19, 2014 California

California Urban Deer Management News and Information Archive

Update on Progress of Deer Sterilization Program at the Villages in San Jose, California

In 2007, the Villages, a gated community with semi-permeable fencing, proposed thinning their deer herd by using archers.  Protests prevented the plan from going ahead.  After discussions, it was agreed that the company White Buffalo would tranquilize the does and perform ovariectomies [some tubal ligations were also performed].  The process began at the end of January, 2013, and was completed in early February.  Below is a recent update on the success of this project.  Based on a prelliminary population estimate and two follow up estimates, there has been about a 20 percent reduction in the deer population in the first year with another reduction of about 20 percent in the second year based on an estimate done in November, 2014 -- about a 40 percent reduction in the population over less than two years. 

The recent report summary appears below.  A complete copy of this report, including data tables, is attached as a word document at the bottom of this page.


Deer Distance Sampling Estimate, The Villages Golf and Country Club, San Jose, California, by White Buffalo, Inc. 11 November 2014


     We used a population estimation method called Distance Sampling as we have over the past 4 years.  This approach is based on the premise that you can determine the width of a transect traveled by creating a detection probability from the field observations (i.e., number of deer and distance from the transect).  In simple terms, the software program projects the area sampled and then integrates the the number of deer observed in that area to determine density.  We used the same non-overlapping spotlighting route that was defined during the population estimate conducted in September 2010, October 2012, and September 2013.  Spotlighting surveys were conducted from 1530-1800 h on 5-9 November 2014.  The transect was 9.1 miles long and was surveyed once each evening.
     While driving 10 mph spotters searched their respective side of the road.  Upon sighting deer, the number in each social group, age and sex of the individuals, ear tag number if present, and the perpendicular distance to the group was recorded.  These data were then entered into a software program (Distance-Version 6.0) that estimated the deer density.  

Distance analysis
     We counted 26–49 deer (14-19 groups of deer) on the 4 transect replicates.  Deer were observed from 0-158 yards from the road, with most observations occurring <60 yards.  The weather was consistent during the observation period; a light wind, clear, and temperatures 65-75 degrees F.   The estimated density for the area surveyed was 86 deer/mile2 (range 65-114).  As was the case in all previous years, deer appeared to be concentrated in the southern and eastern areas of the property, as is evident by the observations recorded on the attached data sheets.   The ~20% reduction is slightly higher other suburban deer mortality rates; typically ~15%.

Detection rates and demographics
     The demographics of the population are ~70% yearling/adult females, ~0% fawns, and ~30% yearling/adult males based on observations during the survey.  In addition to Distance Sampling, we used observations of tagged and radio-collared deer to create a population estimate, given that a high-percentage of the population is marked.  We verified that four collared females died since last October (2013).  We observed 7 of the 9 collared females inside the fence (one is outside - #73) without intentionally tracking them, a 78% detection rate.  We observed 60 tagged females.  If we extrapolate the radio-collared deer detection rates, then we would expect ~75 tagged females to be inside the fence.  This is consistent with observations made this past summer by local volunteers (76 tagged females inside the fence).  We observed 2.45 females for each male.  If there are ~72 tagged females inside the fence (~72 adult females based on mortality since observations this summer), then there are ~30 yearling/adult males remaining (~40% of the number of females observed).  We also counted individual antlered males and took photos of each to tally the known number of adult males present.  We counted a minimum of 26 individually identifiable males.

Fawn recruitment, immigration, mortality, and population estimate
     We did not observe any fawns or untagged females.  We observed 12 relocated deer inside the fence (including one relocated male - #42).  We know of 8 double white tagged deer that have died since October 2013 (#12, 28, 80, and 107; and 4 collared females: #4, 76, 104, and 106) and two relocated deer (927Y/7W, 941W/37W).  There are several females that have not been observed for over a year that could either be dead or emigrated.
     We estimated there to be ~128 deer inside the fence at the completion of our efforts in October 2013, and there are ~102 deer inside the fence presently (~72 adult females based on mortality since observations this summer, and ~30 adult males).  This compares closely to the distance sampling projections that estimate there to be ~95 deer in the 700 acre fenced area (86 deer/mile2 X 1.1 mile2).  Therefore, there has been a net population change of ~20% over the past year.  After the second year it is still very clear that it is imperative to maintain a near 100% sterilize rate to experience a significant population reduction where densities are high relative to the goal (i.e., the Villages’ goal is 40-60 deer).