Golden Gate Park Gophers Still Burrowing, Predatory Birds Flop
By Ryder W. Miller
The growing gopher population at Golden Gate Park is a continuing problem that has still not been remedied despite the presence of predatory birds that live and use the park. The gophers eat the roots of ornamental plants and reproduce in large numbers.
While walking through Golden Gate Park, it is hard not to keep your eyes on the flowering bushes, birds and trees, but when you look off the walkways it is obvious the gophers have been busy. Off the walkways and surrounding athletic fields are thousands of dirt piles that are active or former gopher holes.
Phil Rossi, integrated pest management coordinator, estimates that there are more than 1,000 gophers in the park. Rossi estimates that $100,000 is spent by the SF Recreation and Park Department each year on the problem (a percentage of the 70 gardeners' salaries spent removing gophers).
"A thousand certainly," said Rossi. "Your talking over $100,000 of salary ... as a percentage of the labor involved."
Since gophers are covered by fleas they are unsafe to touch, and they are even more of a health threat when they are dead.
Rossi said the gophers are a prolific breed which can have a new batch every 10 weeks. Many have one to three litters per year. Away from the trails the gopher population can be much bigger.
"It is more of a concern on our athletic fields. It can result in injuries," Rossi said.
Observations of the athletic fields in the park revealed that they had not been encroached upon recently, but the gopher threat is imminent.
Some of the methods used to control the gopher population include Macbee traps (a two pronged pincer trap) and "baiting" (the use of poison pellets).
Rossi relayed that Rec. and Park is using a milder chemical, diphacinone, instead of the more dangerous strychnine, at a dose of half of one thousandth of a percent because of their concern for bird life. Poisons through biomagnification make their way up the food chain and become concentrated in the predators at the top, in this case birds of prey.
"It's a real tough one," said Alan Hopkins, former president of the Golden Gate Audubon Society. "Integrated pest management will never get rid of 100 percent of the species they are trying to eliminate. The predators can never kill 100 percent of the prey species."
Around athletic fields a perimeter of baiting has been created as a line of defense.
Efforts were made to introduce Barn Owls to Golden Gate Park as a gopher predator, but they were unsuccessful.
"The park was too noisy for them," said Rossi. "They took a hike."
They were also disturbed by raccoons that climbed into their nests.
"The habitat isn't really correct for barn owls," said Hopkins.
They prefer large expanses with open fields to hunt. Some of the owls have found homes at Hunters Point.
Botta's pocket gopher (Thomomys bottae) is the most common gopher in the park, said Rossi. Studies reveal that gophers damage plants by eating their roots. At least 46 subspecies of pocket gophers have been observed in California. The diversification of the gophers results from its wide geographic distribution and ecological flexibility. Pocket gophers are found from southern Oregon to northern Mexico and eastward to the Rocky Mountains.
The great blue heron, red tailed hawk and red shouldered hawk are some of the natural predators that live in the park.
"I wish we had more of them in the park," Rossi said.
Gardeners will be getting some help with the gophers from the north. A species of birds called migratory raptors will be trickling through the area beginning in August, reaching their peak by mid-December. The numbers will dwindle through the winter.
The Golden Gate Raptor Observatory notes that large die offs of raptors have occurred recently at Skaggs Island in the San Pablo Bay National Wildlife Refuge, but there is no answer as to the cause.
Recent counts have overestimated the number of sharp shinned hawks and underestimated the number of Cooper's hawks that passed over the Marin Headlands last year.
The recent success of the peregrine falcon, which has been an environmental success story due the discontinued use of DDT, has not had an impact on the gophers because they have not made their way into the park in large numbers.
"They don't use the park a lot because it is not their habitat. Their habitat is the bridge, tall buildings, etc.," Hopkins said. "They use cliff faces ... adapt to tall buildings ... eat shore birds, ducks and pigeons."
While they are not a pleasant sight at athletic fields and trails, gophers are good for turning over the soil in wild habitats.