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Long Term Trends in California's Deer Population

The state's deer population has fallen from the peak of about 2 million around 1960 to around 450,000 to 520,000 in 2015.  The graph at right shows an historical population estimate for California deer.  The estimate is part of an effort to build a statistical model to help understand the reasons for the decline of the California population.  Read a peer reviewed research article demonstrating how public management decisions in California have contributed to the long term decline of the deer population.    Although neighboring states have experienced somewhat similar declines (ecological reasons for decline of deer populations), no state in the West or in the rest of the United States has seen their deer population fall as much as California in the modern era.  In analyzing data from other states, it is clear that no state applies as much hunting pressure to their deer herd as does California measured by hunter success rate.  Link to a peer reviewed paper explaining the population model.  
     Also, California has conducted a bucks only harvest in all but a few years since hunting was resumed in 1927.  Although states often adjust the number of does taken in order to manage the population, no other state has pursued this policy to such an extreme for such a long time as California.  While many other states have made an effort to balance the age of bucks taken, California continues to take a large percentage of young bucks resulting in a few mature bucks in the herd.  As a variety of sources in the right column below suggest, the skewed age and sex demographics as for the California herd, are considered to be problems by many deer managers.

The California Deer Population

Habitat degradation due in part to forest management practices have long been associated with the decline of the deer population.  A statistical correlation of the decline in timber sales in California accounts for 55 percent of the variation in the decline of the deer populations from 1978 to 2012.  Fire suppression and other forest management practices have reduced the amount of edge habitat that support deer and other species.

One method used by deer managers to control deer populations is to change the ratio of buck to doe hunting licenses issued. Killing a large proportion of does will reduce fawn production in the following year, putting downward pressure on the population. Since one buck can impregnate many does, reducing the proportion of does killed and targeting bucks is typically used as a strategy to increase herd growth. Each buck can impregnate more than one doe. During the rebuilding of deer herds during the middle of the 1900’s, many states employed a bucks only harvest to enhance population growth.

California is unique in that it is the only state that has pursued essentially a bucks only harvest for almost every year since 1927 when deer hunting was resumed after a 10 year hiatus designed to protect the herd from over hunting. Since California’s sex and age distributions have generally been about the same, this first pass at building a state population model relies on the reported kill (harvest) to population ratio based on the CDFW population analysis for 1990 to 2009 (data from 2010 to current are reported as preliminary by the department so are not used in the analysis). Also used is the 1947 deer population study conducted by William Longhurst and Aldo Leopold who is considered by many to be the father of modern wildlife management. Note that the estimated kill to population ratio for 1947 reported in Table 1 is within the range of the modern period, 1990 to 2009, so it is assumed this ratio has been relatively constant over time.

Table 1.  Historic Harvest (Kill) to Population Ratios

From recent 1990 to 2009 CDFW Model*

High: 0.0456

Low:  0.0244

Median: 0.348 

From Longhurst Study of 1947 Herd


* Harvest numbers from 2010 to 2013 are reported as preliminary by CDFW, so not used in this analysis

The population estimate appears in the Figure at the top of the page and was estimated by creating eight population scenarios, each using one of the four historic kill to population ratios reported in Table 1 applied against the total buck harvest and also the total deer harvest.  In most cases, these numbers are nearly identical.  On average since 1927 the doe harvest in California has been less than three percent of the total population.  In one year, 1956, the doe harvest was 31.2 percent of the population.  As a result the population estimate for 1956 may be a little high and is one issue under consideration as model development moves forward.  To smooth out year to year anomalies that may be related to hunting conditions or other time specific issues, the population estimate is a three year centered moving average.

In their 1921 report [page 23], the California Department of Fish and Game estimated there were 40,000,000 acres of deer country in the state and that assuming one deer per hundred acres would give 400,000 deer. The estimates are very rough, but in line with the graph at the top of the page. Mortality in that year was estimated as 20,000 killed by hunters, 30,000 killed by mountain lions, and with coyotes and disease added, the yearly mortality would be about 100,000.
The 40,000,000 acres of deer habitat in California equates to 62,500 square miles. Delaware currently targets its deer population at 40 deer per square mile. Applying this target to California would give 2.5 million deer, close to the number of deer estimated around 1960, suggesting a carrying capacity for the state.

News and Studies Related to the Decline of California's Deer Population

Bambi vs. the mountain lion October 2, 2015 California, SFGate [reprint of an article from April, 1967]
... The State has an estimated one-and-a-half million deer.  ... [note that the deer model estimated in the graph in the upper right put the 1967 deer population at around 1.5 million, the estimate above was presented before this information became available, providing an indicate of estimate reliability for our deer model] ...Under the bounty system, from 1907 until four years ago, California hunters collected from $20 to $60 each for slaying 12,461 mountain lions. (1963) ... Assembly Bill 940) ...  would replace the four-year moratorium with permanent repeal...

Decline of California Deer, Big changes for Hunter Education in California May 2, 2015, Examiner
... Dave Casady a Dept. of Fish & Wildlife biologist made a presentation on a study he has been working on regarding the condition, and status of the blacktail deer in a 400 sq mile area of the Mendocino national Forest. This data will be covered in full in a later report, however, the main points coming out of the data was as many hunters have suspected the size of the California Blacktail herd is diminishing by about 10% each year, in this area...

...  Between 2009 and 2013, we captured 137 black-tailed deer (Odocoileus hemionus columbianus) fawns and 57 adult females 1 year of age and older in the Mendocino National Forest ...  Predation was the primary cause of fawn mortality, and black bear predation was the largest single source of mortality. Mountain lion predation was the primary cause of mortality of adult females equal to or greater than1 year old. Does had an average pregnancy rate of 0.87 ±0.05 during our study and carried 1.9 fawns. The estimated asymptotic growth rate for the period from 2009-13 was 0.82 (SD = 0.13).
5) Deer contributed 98.6% of prey biomass to the diet of mountain lions ... Adult female deer with greater access to oak habitats experienced lower fawn mortality from coyotes. Deer with larger amounts of forage within their identified home ranges were less likely to die of any cause, including predation... , we found relative densities of 7.80 (±2.60) to 18.20 (±6.88) males/km2 (3.01 to 7.02 / mi2) and 24.58 (±3.48) to 52.45 (±10.75) females/km2 (9.49 to 20.25 / mi2) in high quality summer range.  8) Our results show that deer in the Mendocino National Forest are currently declining in abundance... 

Deer populations continue decline November 3, 2014 California, Siskiyou Daily
... A dramatic decline in the Siskiyou County deer populations over two decades has triggered concern and a proposed management plan in an attempt to find conclusive evidence as to why the declining numbers continue to persist ... increasing trends in selenium deficiency and predator impacts are of interest ...

B-zone deer population holding steady September 17, 2014 California, Lake County Record Bee 
... The hunter success rate in 2013 for the B zones was 23 percent. Greg Giusti of Kelseyville hunted during the bow season in the B zone at Klamath Mountains and his group counted a total of 557 deer, 24 being legal bucks forked horn or better, during a four-day period.  They also counted 60 spike bucks. [About 15% bucks, 4% mature bucks, not a sustainable demographic] ...

     Although the CDFW's own data show about a 50 percent decline in the deer population from 1990 to 2012, CDFW reported to the Mule Deer Working Group that:  "California’s deer population has been stable to slightly declining for at least the last 20  years. Most apparent is the reduction in migratory deer populations in the northern and eastern parts of the state." [see California Status Update].  The goal of the working group is to "to provide an update on the general range-wide status of mule and black-tailed deer."  The California data misrepresents the state's deer status.

California Zone A deer season opens Saturday August 5, 2014 Lake County Record Bee 
... The drought has had a major impact on the county's and state's deer population...  Approximately 250 bucks were taken in the county in Zone A in 2013, a far cry from the 1950s when the county produced 1,500 bucks annually. Drought, loss of habitat, predators and the increasing human population all have taken their toll on the county's diminishing deer herd... the limit is two bucks forked horn or better...

Deer Diary, California Deer History June 18, 2014 California, Good Times 
... the Huichol. Before the arrival of the Spanish in the 16th century, more than 10,000 people lived on California’s coast between Big Sur and San Francisco. Dating back some 15,000 years ... The deer is the most sacred of animals for the Huichols, the symbol for the heart, intuition, and higher self, says Secunda ...

Why no deer hunting during rut in California? January 14, 2014 Willows Journal
... According to Game Species Conservation Program Manager Craig Stowers, seasons are set with certain harvest objectives in mind. Later in the season as the animals go into the rut (breeding period) they become more bold in their attempts to find a mate, and are thus easier to hunt. If the season was held during the rut, the hunter harvest success rate would be higher, and fewer hunters would be able to hunt before the harvest objectives were reached....

Pumas can't order in, so they eat out May 11, 2014 California, San Francisco Gate
... California's deer population has declined from 2 million in the 1960s to 850,000 in the 1990s and an estimated 445,000 this past winter, according to DFW... The big question is for areas where there are hungry mountain lions, yet there aren't enough deer left to go around: What will the lions eat next? ...

Fish and Game Commission Adopts 2014 Big-Game Tag Quotas April 18, 2014 California, CDFW News
... The California Fish and Game Commission (FGC) finalized big-game tag quotas at their April 15 meeting in Ventura. A total of 204,337 deer [FGC has issued about twice as many tags to kill bucks as there are available bucks in the state.  Hunter success in California is estimated at from 9 to 17 percent, the lowest success rate in the United States where average hunter success is about 55 percent.  Other states adjust the number of tags issued in order to maintain deer populations.  If California hunters have the average national success rate the wild herd will be wiped out.],

Reduction in the number of deer tags recommended April 9, 2014 California, The Trinity Journal 
... Concerned that Trinity County deer herds appear to have experienced a drastic decline in numbers over the past 20 years, the Trinity County Fish & Game Advisory Commission has recommended to the California Fish & Game Commission a reduction in the number of deer hunt tags available here from two tags per person to one and a reduced season in the state regulations scheduled for update this year...

Studies planned to monitor Siskiyou deer herds April 4, 2014 California, Siskiyou Daily 
... Siskiyou County’s deer herds have experienced declining population trends, and two large-scale studies are expected ... helicopter surveys in 2009 covering 308 miles found only 163 deer, with males constituting less than 3 percent of the count... there are also efforts underway at the state level to provide a state-wide deer strategy, but it has been stalled multiple times...

California Deer Winter, 2014, The Official Publication of the California Deer Association
... “Where are the deer?”  There were no signs of predators … There has been no development  … The feed was plentiful and in good condition.  The only thing that was lacking was deer sign...

California Black-tailed Deer, where are they? September 15, 2012, Jeffrey Banke 
... As a photographer ... searching for black-tailed deer to photograph became more and more difficult to locate animals this year ... interviewing Sierra Pacific employees who are in the woods logging for months at a time who have seen very few deer confirm this observers own research. It would seem in conclusion, that if we do not have some radical changes in both the wildlife management approach by the DFG ... then we are on a continuing downward spiral... [Jeff Banke is a freelance photographer who has been teaching Hunter Education for the California Dept. of Fish & Game for 18 years, is one of only 7 Master Instructors in the State.]

Predators and Prey—A Case of Imbalance, Mountain Lions and the North Kings Deer Herd "Forest Research West", June 1989
In the study area on the west slope of the Sierra Nevada, apparently mountain lion numbers have increased while deer numbers declined to about one-eighth their peak numbers in the 1950s.. In the study area on the west slope of the Sierra Nevada, apparently mountain lion numbers have increased while deer numbers declined to about one-eighth their peak numbers in the 1950s. Neal, along with George Steger (also with PSW), studied the California mule deer in the Sierra Nevada from 1970 to 1985 as part of an interagency effort to reverse the decline. This effort showed that the decline was primarily due to loss of fawns during the first 6-8 months of life.

A paper describing how changing forest management practices have reduced deer habitat in California, CDFG, Habitat Guidelines for Mule Deer, 2007

Drought May Account for Uptick in Deer Harvest 
The reported deer harvest has risen from the record low of 10,892 in 2010, but the increase corresponds the the persistent drought in California that has worsened significantly into 2014.  Deer searching for food and water are more active and so are more likely to by killed during the hunt.  Deer collisions reported to the California Roadkill Observation System in 2014 have risen dramatcially over previous years, indicating the deer are moving around in search of food and water.

California Drought Greatly Affecting Wildlife May 15, 2014 Guardian Liberty Voice
...  inland California’s already declining population of deer is having a very difficult time with a loss of vegetation and sufficient water supplies. Deer will be forced to migrate to new land in search of adequate food and water ...

Historic Use of Fire

Even in 1542, Southern California's air quality was in question August 22, 2015 The San Luis Obispo Tribune
... During the 19th century, many recent arrivals from the East and Midwest thought the fires were deliberately started by Native Americans to facilitate their killing of wild game ...  historical documents, indicate that Native Americans employed extensive burning of chaparral and shrub lands as a means of land management. They sought to turn the former into native grasslands to promote the proliferation of deer, antelope and small game...

Monterey Bay Area’s Native Amah Mutsun Seek Return to Lost Way of Life July 21, 2016 California, 90.3 Kazu
... The Amah Mutsun Tribal Band wants to restore ecosystems that once flourished here: from the deer herds that roamed the land to the medicinal plants that sustained the tribe...They may use controlled burning to maintain grasslands ...

Analysis of Data Related to the California Deer Population

California has conducted a virtually bucks-only hunt for all but a few years in the since about 1927, the only state following this policy for so many years.

The California Department of Fish and Wildlife (CDFW) estimated 512,000 deer in 2015 up from 443,289 deer in 2014.  The population estimate for 2015 that CDFW presented to WAFWA was a range of 450,000 to 550,00, better reflecting the estimation reliability. 
     Changes in the deer harvest collection process and delays in reporting data from the California Department of Fish and Wildlife make it difficult to estimate the 2015 and 2016 population.   Data from the U.C. Davis Roadkill project point to a "troubling decline" in deer numbers for 2015, consistent with the expected outcome of prolonged drought.   Road kill data had jumped in 2014.  Deer appear to have been to be moving around more in search of food of water in 2014, hunter success went up somewhat in 2014, a common result of scarce food supplies. Nevada estimated a population decline as a result of the drought in 2015. Preliminary California 2015 harvest data is higher, but the state implemented mandatory reporting which is expected to increase the reporting rate.  In January, 2016, the state considered dropping the target number of deer tags for 2016 from 196,680 to 127,000. 
     CDFW declines to explain the details of  its population estimation method. We filed a freedom of information request and got one small, undocumented spreadsheet that seemed to assume a downward future trend for the population.  This peer-reviewed research article, starting on page 159, documents previous information on CDFW's website that significantly overstated the relative abundance of deer in California.   
       CDFW estimated the population at 850,000 in 1991, 1.5 million in 1967.  The graphic below shows the CDFW's estimate for the California population since 1991 compared to the reported deer harvest [click on graph 
to enlarge]. Recent population estimates from CDFW do not track with the declining deer harvest data.   Habitat loss, fragmentation, and fire suppression resulting in denser forests have been major factors contributing to the decline of deer populations throughout the West. The decline in timber sales corresponding to reduced logging activity is highly correlated to the decline of California deer populations.  Buy a paper bag - save a deer.  Also contributing to the population decline in California appears to be the large number of deer tags issued by the Game Commission.  
     In 2014, the Game Commission authorized about twice as many buck tags as there are available bucks in the entire state. Given the history of a large number of tags issued, hunter success in California is often lower than in any other state.  If California hunters had the national average hunting success rate, the wild herd would be wiped out. CDFW generates about $25 million in revenue annually from the sale of tags.  
      Evidence suggests that another contributing factor in California may be the long-term policy of  essentially bucks only hunting, resulting in highly skewed deer population demographics, as might be found in a poorly managed game preserve.  The reported 2013 harvest was 13.8% of the peak harvest reported in 1956.  No other state in recent history has experienced this much of a decline. No other state has followed an essentially bucks only harvest nearly as long as California. [see a peer reviewed journal article documenting these issues] The state also takes a high percentage of young bucks, resulting in relatively few mature bucks. The national management trend is to balance herd demographics. Deer managers around the country often comment to the press about the dangers of persistent skewed demographics. A 2009 study of deer in Siskiyou county found only 3 percent males.  During the 1960's, when Idaho was selling too many tags to sustain the herd and overstating the population numbers.  The people of the state pressured the agency, tag sales were reduced, the herd recovered.  Same basic story in Colorado during the 1990's. 

Read articles from other deer populations related to the probems of deer management in California:  habitat, herd demographics, 

Deer Friendly,
Nov 15, 2016, 5:38 PM