The distinctive splayed antlers of black-tailed deer bucks have become an increasingly rare sight in California, particularly if you are accustomed to spotting the appendages through a rifle scope.
The California deer population has plummeted over the past two decades - by 46 percent - if the yearly count of bucks killed by hunters is a proper measure.
A team of scientists led by the California Department of Fish and Game is fanning out across the rugged mountains of Mendocino, Glenn and Lake counties in an attempt to figure out just what is going on.
"The deer population harvest has been steadily declining," said David Casady, an associate wildlife biologist for the Department of Fish and Game. "One of the things we're studying is whether the population has decreased or just the harvest. Most likely it's the population that has decreased and the harvest is just tracking that."
The Columbian black-tailed deer, or
Odocoileus hemionus columbianus, is the smallest, darkest and most common of the three deer species that are prevalent in California, with bucks weighing up to 200 pounds and does topping out at 140 pounds. The other two most abundant deer species in the state are the California mule deer and the Rocky Mountain mule deer.
Black-tailed deer, combined with mule deer, inhabit about 75 percent of California's wildlands. They thrive on the edges of forests, where they can find the underbrush and grasslands they prefer and still find places to hide from predators.
Antlers, venison sought
The males grow multipronged antlers, which, along with the promise of venison, is a primary reason they are the state's most popular game mammal.
The number of bucks taken by hunters in California dropped from 27,846 in 1989 to 14,895 in 2009, according to Fish and Game statistics. That was out of 164,753 hunters who pursued deer in 2009.
The three-year study, which is being done in coordination with UC Davis, is documenting habitat changes, vegetation, predation, land use patterns and other factors that might affect black-tailed deer. It is focusing on the mountains east of Covelo (Mendocino County) because that area has historically had some of the best deer habitat in the state and has, for the most part, been unaffected by human encroachment.
57% drop in area
The area has nevertheless seen one of the biggest declines, from 3,013 deer harvested in 1989 to 1,297 in 2009, a 57 percent drop, according to state statistics. The state estimated that 38,037 people hunted deer in the area in 2009.
Heiko Wittmer, a UC Davis adjunct professor and senior lecturer in conservation and ecological restoration at New Zealand's Victoria University of Wellington, said he and several doctoral students began capturing deer last year and equipping them with collars and tags with radio and global positioning satellite technology.
So far, he said, 40 fawns have had their ears tagged and 26 adults have had collars placed around their necks.
The equipment alerts trackers if four or more hours pass without any movement, an indication that the animal has died. The researchers then use an antenna to find the animal. The goal is to perform necropsies within 24 hours to determine the cause of death and use DNA analysis to determine what, if any, predator was involved.
"We are trying to estimate survival rates for fawns and for adults," Wittmer said. "Once we have that information, we can accurately measure death and birth rates and see if all of that together would result in a decreasing population."
Cougars, bobcats, black bears and coyotes are known to feed on deer. Remote cameras are being used to monitor coyotes and other predators, but only the mountain lion is known to have taken down a full-grown deer. That's why researchers have also collared a female mountain lion. They are planning to collar and track five additional mountain lions during the study, which is funded through June 2012, Wittmer said.
"One neat aspect of this study is that we are simultaneously looking at predators and prey," Wittmer said. "There is a lot of debate right now about whether the lion population is too high."
Hunting groups have claimed there are too many predators because of harvest restrictions and the elimination, albeit a long time ago, of bounties on mountain lions and coyotes.
Another theory, espoused by a fair number of biologists, is that the brush, grasses and foliage that deer feed upon are being choked out by nonnative weeds. The lack of food, the hypothesis goes, is being exacerbated by California's vigorous suppression of wildfires, which historically served to renew the state's grasslands and forests.
Forces of nature possible
The plummeting deer population could also be the result of a combination of factors, Casady admitted, including the tendency of hunters to fill with lead any buck with big antlers that they spot. Could it be that only the ugliest, nerdiest bucks are left and the does are simply turned off?
"It doesn't take many males to make sure all the females are bred," Casady said. "If the population was really that bad off, I think they would still breed with the ugly ones."
It may turn out in the end, Wittmer said, that the declining deer population is simply a reflection of what is normal in a balanced ecosystem.
"Maybe," he said, "if we want to have both healthy deer populations and healthy predator populations, then these densities are more natural."
The decline of black-tailed deer
-- Hunters killed 27,846 black-tailed deer in California in 1989 compared with 14,895 in 2009, a 46 percent decline.
-- Hunters killed 3,013 black-tailed deer in the study area in the forested mountains of Mendocino, Glenn and Lake counties in 1989 compared with 1,297 in 2009, a 57 percent decline.
-- Deer, which inhabit 75 percent of California's wildlands, are the most popular game animal in the state, attracting as many as 200,000 hunters a year.
-- Researchers have tagged 40 fawns and placed radio collars equipped with global positioning technology on 26 adult deer.
-- Cougars, bobcats, black bears and coyotes are known to prey on black-tailed deer and all four killed or scavenged fawns during the study, but the mountain lion is the only predator known to have taken down a full-grown deer.
-- A female mountain lion has been fitted with a satellite GPS collar and five others will be collared during the study, which is expected to continue through June 2012.
Source:
SF Chronicle
