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One Square Mile - The Sequel

Posted: January 6, 2015

In a previous post we warned you that not all buck home ranges are 1 square mile. Home range size depends on where a deer lives in Pennsylvania and you may be surprised by how much home range size varies.

A recent graduate of our program, Mr. Tyler Evans, recently completed his M.S. degree investigating deer home range size because it has implications for how chronic wasting disease can spread. Tyler took all of the GPS location data we had for white-tailed deer in Pennsylvania to look for patterns. And he found something really interesting.

Tyler found that as the forests on the landscape became more fragmented that home ranges of deer got smaller. He defined four types of forest landscapes: highly fragmented, fragmented, divided, and contiguous. We'll show you what we mean by each type.

We collared deer in Gettysburg National Military Park where the forested habitat is highly fragmented. Notice in the image below how the patches of forest consist of small woodlots or narrow strips along streams. 

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We also collared deer in Armstrong County and up in WMU 3C where the forests are fragmented, but not to the extent they are in Gettysburg.

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Our current study areas on the Rothrock and Bald Eagle state forests in the Ridge and Valley region of Pennsylvania, are where the forests are divided - with forested ridges and non-forested valleys.

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And the opposite of fragmented is found on our study areas on the Susquehannock State Forest - contiguous forest - which is simply a fancy name for the Big Woods. The only non-forest habitat here is only temporary - when timber is harvested.

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So what did Tyler find? I first show you data for females, just because we happen to have more data and the patterns are easier to see. In the boxplots below the dark horizontal lines are the average home range size, the boxes represent the middle 50% of home range sizes, and any extreme home range sizes are open circles outside the whiskers.

nullNotice how as the forest becomes more fragmented the home ranges get smaller. In the Big Woods (contiguous forest) the average home range is about 1 square mile (for females!). And we almost never found a female with a home range less than half a square mile.

But in Gettysburg (highly fragmented) most home ranges are less than a quarter square mile in area! And we never found a female with a home range bigger than half a square mile.

So what about males? Well, we don't have quite as much data (in fact we lack any males from the fragmented landscapes) so it's more difficult to detect a pattern. But look how male home ranges average 2 square miles in more forested habitats but less than one square mile in Gettysburg (highly fragmented).

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An important question is why do home ranges differ so dramatically? Tyler hypothesized that in fragmented landscapes there are more food sources available so deer don't need as big a home range. Also, deer densities are higher in places like Gettysburg compared to the Big Woods - that means a male doesn't have to travel as far around Gettysburg to find the same number of females.

Consider this. In Gettysburg an average buck home range (~0.5 sq. mile) encompasses about 2 female home ranges. In Susquehannock State Forest, an average buck home range (~2 sq. miles) encompasses about 2 female home ranges!

As I warned in my previous post about deer home ranges, the rule of thumb that a buck's home range is one square mile is most often wrong. Home range size varies greatly depending on the landscape where a buck lives - and that goes for doe too!

-Duane Diefenbach

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