A few weeks ago I talked with some biologists at the Wild Things 2009 conference. They told me my backyard had been invaded by Gray Squirrels — and I had totally missed it!
The last time I paid attention to our backyard squirrels was years ago, as the boys were first getting interested in birds. Ethan pointed out a gray looking squirrel among the many rusty looking Fox Squirrels. I think I wrote it off as just a color variation. Little did I realize that we had seen the vanguard of a force that was gradually pushing Fox Squirrels from our neighborhood, replacing them with slightly smaller Gray Squirrels.
Biologists from University of Illinois at Chicago documented this invasion. They used walking surveys and citizen scientists to collect their data. The team has resumed collecting data on their Project Squirrel website, so I just submitted our first results: Gray Squirrels 8, Fox Squirrels 2. In 2002 less that 1 in 10 squirrels in my neighborhood were Gray Squirrels; my 2009 results found 8 of 10 were Gray — an almost complete reversal. I’m so embarrassed that I missed this big change in our neighborhood!
I think we missed the change for several reasons. We are birders now, with our own kind of tunnel vision. We didn’t look at squirrels very closely, and when we did we only saw their backs. Most Gray Squirrels here have rusty patches on their backs; we never noticed that their bellies were white. (If you want to learn to differentiate Gray and Fox Squirrels, go to this page on the Project Squirrel site.)
So, we’ll be submitting data to Project Squirrel several times a year. It’s a really easy process — you should give it a try! We’ll also be watching squirrel behavior much more closely: What natural foods do we see each species eat? Which species get eaten by hawks or canines at Columbus Park? Which species reproduce successfully this year? We’ll keep you up to date with our results.
Note added May 1, 2009: I submitted another observation, for today, May 1, 2009: Gray Squirrels 4, Fox Squirrels 2. That’s pretty typical of the last month. There have been fewer Gray Squirrels visible at any given time. I’m wondering if their numbers are really reduced, or if they’re not all coming at once because at least one parent stays with the nest of young.
Also, we have not yet seen baby squirrels this year, as far as we can tell. We’ll submit again when we do.
Note added May 5, 2009: An article about Project Squirrel appeared in the Chicago Tribune‘s online edition today. Go here to read the article. (The link may only be good for a few weeks.)
Note added June 8, 2009: At 6:15 a.m. Aaron and I saw five Fox Squirrels in our backyard at once, without a Gray Squirrel in sight. That’s a record for this year! Then they got into a fight and chased each other into the neighbor’s pear tree. (Now there’s just one Gray Squirrel.)
The Fox Squirrels all looked full sized, but we wondered if some might be this year’s young.
Some background information and references:
In addition to looking at the Project Squirrel website and talking with biologists at Wild Things, I also read two scientific papers written by Project Squirrel researchers (see below). Both studies included field work in our hometown of Oak Park, Illinois. The 2005 paper has maps showing changes in Oak Park squirrel distribution between the late 1990s and 2002.
van der Merwe, M., Brown, J. S., & Jackson, W. M. (2005). The coexistence of fox (Sciurus niger) and gray (S. caroliniensis) squirrels in the Chicago metropolian area. Urban Ecosystems, 8(335-347).
van der Merwe, M., Burke, A. M., & Brown, J. S. (2007). Foraging ecology of North American tree squirrels on cacheable and less cacheable foods: A comparison of two urban habitats. Evolutionary Ecology Research, 9, 705-716.