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Davis, California

Saturday, March 2, 2024

UC Davis to test birth-control on squirrels

Apparently nothing gets hormones pumping like climbing trees – or they’ve all maxed out their 10 free condoms per week from the Love Lab. Whatever the reason, it’s been the eastern fox squirrels’ time of the season for loving for too long – and their campus population has become unmanageable, spawning a birth-control research program.

“They’re an invasive species in California,” said Sara Krause, the doctoral student in the department of ecology in charge of the program. “They’ve only been here seven years and they have no natural predators in the area, especially not on campus.”

Krause said there’s no definitive answer as to how a squirrel that belongs in upstate New York made its way to California. Speculation is that they came by car, either as someone’s pet or as stowaways.

“And then they arrived safe and happy, and the birds and the bees took over,” said Sal Genito, director of the Buildings and Grounds division of Facilities Management.

Eastern fox squirrels (Sciurus niger) are between 10 and 15 inches long, and weigh between 1.5 and 2 pounds. They can be identified by their orange-brown color coat and bushy tails with reddish topped hair, according to Americazoo.com

A birth-control research program to combat the population explosion will begin next week, in which traps will be laid under trees and around lawns. Ensnared squirrels will be looked at, marked with a dye and freed to be observed by researchers through fall and winter.

Squirrels with dyed tails will be brought back in summer and given a hormone injection to prevent reproduction, while others will be given a placebo for comparison. If squirrels administered the real injection act differently, it will prove the hormone successful.

The program intends for the population of eastern fox squirrels to then plateau, before declining to a small, sustainable number in five to 10 years.

Birth control is the most non-invasive, humane way to go about limiting the population, said Krause. The traps are simply wire mesh inviting the squirrels in to eat the acorn before the box shuts. The boxes give them room to move around, and will be covered with canvas – about as comfortable as a temporary shelter for a squirrel can be.

The birth-control idea was a product of public outcry to the previous eradication method of poison bait.

“Lethal control is very challenging, because it’s socially unacceptable,” said Krause. “Poisons are also difficult to aim and it’s hard to ensure they don’t end up in non-target species.”

Not administering birth control puts the campus community at risk for several things, including injuries.

“More and more eastern fox squirrels are approaching students on the Quad and at Lake Spafford,” Krause said.

While nobody has been hurt yet, encounters are dangerous because of the bacteria squirrels carry and the skin infections or stomach and intestinal illnesses that can result from scratches or bites.

Crops threatened by overpopulation include almonds and walnuts at campus research farms and orchards, and the bark of redwood trees in the arboretum.

Ecologically, the non-native squirrels cause competition with plants and animals that are native to the area, said Krause.

“Eastern fox squirrels eat the same foods as native gray squirrels and birds,” she said. They have also been known to eat eggs and baby birds.

Genito said they’re entrusting the student body to be respectful of the experiment.

“We’re hoping people see these traps around campus and leave them alone,” he said. “There’s a lot of passion on both sides of the issue – other people want to leave it to nature and let the population take over, so it should be an interesting couple of years seeing how this goes.”


MIKE DORSEY can be reached at adbonde@ucdavis.edu.







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