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Too many deer leave the San Juans vulnerable to invasive plant species, says UBC study

With their chestnut hides, magnetic black eyes, and twitching nubbin of a tail, the sight of deer against the backdrop of a forest is charming.

Not so charming is their effect on a small parcel of land.

Growing deer populations are fundamentally changing the environment of the San Juan Islands and the Gulf Islands off the coast of B.C., leaving the region susceptible to invasion by non-native plants, according to a recent study by researchers at the University of British Columbia.

“These changes are not the result of natural processes,” says Tara Martin, adjunct professor in the Faculty of Forestry at UBC and lead author of the study. “The environmental changes are an indirect effect of humans. We’ve removed the large animals that preyed on deer and changed hunting policies.”

Researchers looked at the density of black-tailed deer on 18 Southern Gulf and San Juan Islands with forest ecosystems. The study, published in the journal “Biological Conservation,” found that the number of birds and plants decreased on islands with higher deer densities.

Islands with more than one deer per 2.5 acres had half as many birds as those with low deer density. Deer graze on shrubby vegetation for food, and song birds, such as hummingbirds, sparrows and warblers, depend on this vegetation for nesting and feeding. Researchers found that islands with moderate or high deer density had less shrubby vegetation and half as many birds as those with low deer density, or one deer per 247 acres. By reducing or eliminating native plants, deer also facilitate the invasion of non-native species, reducing the biological integrity and aesthetic appeal of the region.

Islands studied in the San Juans were Ewing, Flattop, Little Sucia, Matia, Patos, Sucia, Yellow, McConnel, Sentinel and Jones. Although those islands are primarily unpopulated by humans, the results are likely similar to what is happening on larger islands like Orcas, San Juan and Lopez.

“I suspect, based on my experience, that the situation is similar to identical in much of the San Juans,” said Peter Arcese, professor in the Faculty of Forestry and co-author of the study. “However, it is harder to pinpoint deer impacts on large islands like San Juan or Orcas, because of ‘de facto’ management regimens we are not aware of. E.g., dogs off leash appear to have marked impacts on deer populations and their impacts on vegetation and birds. However, papers ... show that similar processes also occur on large islands.”

One factor on the bigger islands is deer fatalities on county roads. In 2007, public works picked up 135 dead deer. In 2008 that number was 136; in 2009, it was 159; in 2010, it went down to 79.

“On all three islands this last year we mowed back the right of way on the main roads,” said Russ Harvey, operations manager for public works. “It gives people more of a chance to see deer coming.”

Possible solutions

Researchers suggest that changing regulations and sentiments towards deer hunting have allowed populations to thrive, and may lead to greater numbers of local plant and bird species on threatened species lists in the future.

“As plant species decline, it is inevitable that birds, insect pollinators and other species will also decline,” Arcese said. “I work with several small island communities that have seen dramatic change first hand but are prevented from hunting by local bans.”

Joe Gaydos of the SeaDoc Society on Orcas says a study was conducted 10 years ago in the Queen Charlotte Islands produced similar findings.

“This is one of those things where hunting, done in a safe way, offers a solution,” he said. “If people see someone hunting, they should know it’s not necessarily a blood sport. They are helping the environment and providing food for their families.”

Arcese says the results of the study, which was funded by the Natural Sciences and Engineering Research Council of Canada, are considered “old news,” as many regions – both in the U.S. and world-wide – have already linked decline in native vegetation with the overpopulation of deer.

“We’re hoping to convince government that they need to consider new management initiatives, such as limited entry hunting under community supervision, because failing to act is a decision to favor the black-tailed deer over many other species native to our region and valued by humans,” Arcese said.

The Washington Department of Fish and Wildlife’s harvest report says 697 deer were harvested in 2009 from game management unit 410, which includes San Juan County, Whidbey, Camano, and some of the Skagit County Islands. The data is not broken down by island, except for the second deer permits, of which 30 are issued per year. In 2009, 52 deer were harvested from that second pool. The numbers for 2010 are not yet compiled.

Arcese concedes that many people are not comfortable with reducing deer through hunting.

“However, fertility control has proved expensive and ineffective in most situations where it’s been tried,” he said. “Re-introduction of predators we’ve removed from the islands – cougars/wolves – is generally even less popular, though effective. It is very important for people to understand clearly that to avoid dealing with abundant deer in some fashion nearly ensures ... the continued loss of biodiversity and native plant and bird richness.”

Current hunting regulations

To hunt deer in Washington, you must purchase a big game hunting license. There are three ways to kill a deer: shotgun or pistol, muzzleloader, or archery. Local regulations require a hunter to carry written permission of a land owner when hunting on private property. Hunters are allowed to “bag” one deer each season with a valid hunting license and the purchase of a deer tag. Hunters can apply for a second, island specific tag each year. There is a drawing for 30 second deer permits for each of Shaw, Lopez, Orcas, Decatur, Blakely, Cypress and San Juan Islands.

There are different seasons for each method of hunting. For season dates, visit wdfw.wa.gov/hunting.

The jail time and fines for breaking hunting rules is steep. This past November, four men were accused of flouting state rules and hunting deer at night on San Juan Island. Fish and Wildlife typically takes the lead in cases that involve possible hunting violations.

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