Another Year’s Squirrel Data

by Carl Strang

At the end of March I completed my third year of collecting data on habitat preferences of fox and gray squirrels at Mayslake Forest Preserve. The basic question is whether the usual preference of fox squirrels for savanna habitat and gray squirrels for forest will hold in an area where the savanna is high quality and the forest is low quality.

Fox squirrel

Over the first two years it was clear that both species preferred the savanna, but that preference has been stronger in the fox squirrel. This year the results were a little different. The area involved, 54.6 acres altogether, is 64% savanna and 36% forest. In the first year, 82% of fox squirrel observations were in savanna, 90% in the second year and 92% in this year just ended. The corresponding numbers for gray squirrels were 73%, 79% and 65%. That last number was perhaps the most remarkable, gray squirrels in the past year appearing in the exact proportions of the two habitat types on the preserve.

Gray squirrel

That is the only number in this entire study that shows no statistically significant difference from expected values (actually, the chi-squared test statistic is calculated from the numbers of observations rather than the percentage values; this year I had 157 observations of fox squirrels, 75 of gray squirrels). I continue to gather these data each year because the preserve continues to change, thanks to the efforts of the restoration team. High quality savanna is improving, and low quality forest is being cut back.

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