Awww. Isn't this squirrel just so cute? You might think that now, but stare long enough at the beady eye of this Eastern Fox Squirrel (Family Sciuridae : Sciurus niger Linnaeus), and you'll see that it's actually a reproducing nightmare overrunning a campus or orchard near you. In fact, the Eastern Fox Squirrel is reproducing so quickly that researchers at the University of California Davis are putting them on birth control.

Sara Krause, a UC Davis ecology doctoral student, will be leading a birth-control research program to prevent a population explosion of these non-native tree squirrels. Krause earned a bachelor of science degree in natural resources at Cornell University (another campus well-populated with tree squirrels).
Her faculty adviser is Douglas Kelt, professor of wildlife, fish and conservation biology, and member of the Graduate Group in Ecology.

"In seven years, we went from having no eastern fox squirrels on the campus to having more than 400, and there is currently no sign that their reproduction is slowing down," Krause said. Eastern Fox
Squirrels are not native to the Davis area. In fact, they more typically find their homes throughout the eastern and central United States, south into northern Mexico, and north into Canada. However, they have been introduced multiple times into Sacramento and Bay Area, so they might have migrated over.

The non-native squirrels are potentially problematic, and if left unchecked, could negatively impact Davis in more ways than one. The campus has 5,300 acres habitats, from dining halls to woodlands and from student gardens to almond orchards. The spread of Eastern fox squirrels threatens agricultural land—they’ve already started chewing the bark of campus redwood trees, which could weaken and even kill a tree. The squirrels also compete with native gray squirrels, and can eat bird eggs and nestlings.

During the program, faculty wildlife experts and students will place humane live traps of wire mesh, under trees and around lawns to capture the bushy-tailed critters. The captured squirrels will then be examined and set free after being marked with a nontoxic dye. Throughout the fall and winter, the tagged squirrels' behaviors will be studied. Later, they will be recaptured. Some will be given birth control hormone injections to prevent them from having offspring, and others will be given a placebo of sterile saline to serve as a scientific control for comparison. All the squirrels will be set free and then studied to see how the hormone is affecting them. If the treated animals exhibit different behavior, but the control
animals do not, this will serve to confirm that any changes were related to the hormone injections.

There already exists a similar Trap, Neuter, Return method to control feral cat populations, where cats are humanely trapped and then spayed or neutered, the difference being in that the squirrels will not be surgically "fixed", but injected with a hormone means of birth control, similar to Depo Provera that women take, which should last about two years as an effective means of birth control.

To identify those squirrels who have been treated and who have not, they'll be tagging them with ear tags, little metal earrings with numbers on them. They'll also use PIT (Passive Integrated Transponder)
tags as a second means of tagging, which are similar to what many vets put into pets.

When they recapture the squirrels, researchers will check their overall condition and examine the injection site. "We want to know if this is an effective and safe means of control. We'll look at reproductive status," says Krause. "In order to test how effective the birth control is, one of the thing you can do is take a small amount of blood and test for hormone levels."

The first injections will begin in the summer, and the program would last for about two years. Ideally, according to Krause, they hope to see, “a decrease in the reproduction of treated individuals. Because that means its an effective means of birth control. Secondly, to test behavioral differences for those squirrels who have not been treated and those who have, and thirdly, to create a scientific model that would indicate what portion of the population needs to be given birth to control for it to be an effective means of birth control.”

“We also want people to understand why this is being done. The squirrels are a threat to human health, threat to native wildlife–they compete with the native western great squirrels, they eat bird eggs and nestlings, and they affect agriculture in the area.”

Contact: Sara Krause (pronounced Krow-zee), Graduate Group in Ecology, (510) 418-7220,