Population control | Although the Richardson’s ground squirrel can cause havoc, researcher stresses humane control
She is in the mood for love for only two hours on one afternoon of one day per year.
That is the surprising biology of the female Richardson’s ground squirrel.
The male’s sexual lot is only slightly better: he produces sperm for four weeks of the year and must time his mating activities with those precious two hours per year when the female will accept him.
Given those restrictions, why do ground squirrels, commonly but incorrectly called gophers, seem so plentiful?
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Gail Michener, professor emeritus at the University of Lethbridge who has made a career out of studying Richardson’s ground squirrels, told a Nov. 30 lecture that the mobility of males and the ability of females to mate with multiple males is part of the reason for ground squirrel numbers.
Ground squirrels have only one litter per female per year of six to eight offspring per litter.
Even so, there may not be as many of the rodents as farmers seem to think, depending on conditions.
“The big problems have happened in recent years where we’ve had these drought years,” Michener said in an interview after her lecture.
“Two things happen under drought conditions, one of which is the crops don’t do very well,” she said.
“Ground squirrels of course evolved here on the Prairies so they can cope with drought. And you can see them more easily amongst the sparse crop, so there may not necessarily be more of them but they are easier to see and the farmer has already got a problem with growing a crop that’s not thriving under those conditions.”
Michener has studied Richardson’s ground squirrels for 30 years at three sites in southern Alberta. Little was known about the life cycles and behaviours of the ubiquitous prairie rodents until her ground-breaking research began.
“In the 1960s, little was known about them except how to kill them,” said Michener.
The mammals’ habits of digging holes and eating crops make them the common bane of farmers.
Michener amassed a wealth of information from years of in-field research, in which she trapped, ear-tagged and painted the rodents with hair dye for identification.
Her admiration of the species was evident in her lecture, although she is aware that her research can be used in part to kill ground squirrels that are considered troublesome.
“I certainly accept that there are situations under which the numbers of ground squirrels reaches the point where it’s definitely going to have an impact,” she said.
Strychnine is a commonly used poison to kill ground squirrels. Though effective, it won’t eliminate them for long periods because they will re-invade when there is an existing burrow system and when environmental conditions are right.
Michener said farmers need to accept some loss to ground squirrels, just as they accept some grain losses out the back of their combines.
“You make a compromise there, and so there’s probably compromises that we can make with the ground squirrels, too. Tolerate this many, and once it gets to that many, do something about it.”
Ideally, adults should be controlled in early spring, before many of them have mated. Females generally become pregnant within 10 days of emerging from hibernation. About one month later, there are six to eight times as many ground squirrels.
“Now you’ve got a big task and it’s not really the right time to deal with it because you’ve got a bigger job than you would have had if you’d taken action in the spring.”
Adult males enter hibernation in June and females in July, so poisoning in summer will kill juveniles but has no impact on adult populations.
“They will come back next year even if you manage to get rid of the juveniles,” Michener said.
She said farmers may not consider it,but there is a humane element in the timing of control efforts.
“What I really hate is when people do their controlling when the females are lactating because I know the baby ground squirrels are sitting underground waiting for their mommy to come with milk. She never comes and they slowly starve to death.
“I think farmers should be humane, and so if they’re going to control, they should control first thing in the spring, as soon as the animals are coming out of hibernation.”
