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(8-8-11) - Note to readers: Click HERE for more detailed analysis on where in the Tidewater area that alligators might move in and not be forcibly moved out in the next decade or so......
So, I've been following my web traffic with my little buddy Sitemeter. I've seen some interesting trends develop over just the last month or two since I installed it. The most unexpected has been the volume in web traffic I receive from people searching for "alligators in Virginia" and finding my first post on the topic. Since apparently this is a hot topic among internet users (who knew?) I thought I'd look into the topic a little further (as I've been meaning to do for over a decade). Remember that I mentioned the USFWS Habitat Suitability Index Model for Alligators? Well, I downloaded it, read it, and figured out the model. It's an interesting one. The results are in the excel worksheet above, but what fun is that? Here's what I learned....
So, I've been following my web traffic with my little buddy Sitemeter. I've seen some interesting trends develop over just the last month or two since I installed it. The most unexpected has been the volume in web traffic I receive from people searching for "alligators in Virginia" and finding my first post on the topic. Since apparently this is a hot topic among internet users (who knew?) I thought I'd look into the topic a little further (as I've been meaning to do for over a decade). Remember that I mentioned the USFWS Habitat Suitability Index Model for Alligators? Well, I downloaded it, read it, and figured out the model. It's an interesting one. The results are in the excel worksheet above, but what fun is that? Here's what I learned....
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First of all, as I sort of mentioned before, we have to blissfully ignore and/or accept three admissions made by the creators of this habitat model. First, though I suspect they were tasked by USFWS to create this model for the entire country, the authors created a habitat model only for the northern Gulf of Mexico (TX, MS, LA, FL panhandle). Second, a lot of geographic assumptions in their text are based on a 1958 field guide to reptiles and amphibians. That's more embarassing than the first thing, for sure. Third, the authors admit (I missed this on my first read) that they never actually field tested the model. And as a habitat ecologist, I can say that that's incredibly pathetic. But you know what? It's better than my model, because I don't have one.
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So I entered all of their variables for these sites into their mathematical model for 15 sites near the NC/VA border where alligators are not recognized to exist naturally, 2 sites in NC where they are recognized to be reproducing successfully, and 1 site on the Gulf in TX that is supposedly renowned for its gator population. I did not use 5 sites out of the 18 because once I started working with the HSI model, it was clear that they would score very poorly. As the authors of the HSI recommended, I did my analysis of each habitat "factor" through a combination of memory of some of these areas, photographs I could find, and aerial photos (I used Google Earth). So, are there gator-compatible habitats in Virginia, based on a mathematical model created by the USFWS, who propose that alligators do not live in Virginia?
.Absolutely. But I was surprised by the results. You'll recall (links above) that the two closest reproducing populations are at Alligator River NWR (on Albemarle Sound, 60 miles south of the VA border) and Merchant Millpond State Park (in the inland forested swamps, less than 25 miles south of the VA border, with gators occasionally - and officially - spotted within 12 miles of the border at Dismal Swamp State Park).
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So what? Well, according to the HSI scores (see below), the highest quality alligator habitats near the VA-NC border are where Back Bay meets the Currituck Sound.....60 miles north of Alligator River NWR. Inland, this is not true, as marginal, patchy habitat occurs just over the VA line within the Dismal Swamp. This probably goes a long way toward explaining why alligators have not moved north faster. A pretty basic conclusion is this: Alligators expanding northward on the coastal sounds are likely to settle on other territories far south of the VA line - they need to go no further. Alligators expanding northward in the interior swamps are likely to find low-quality habitat, and any net progress northward is haphazard.
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The HSI scores backed up my analysis...the three reference sites (known gator habitat) scored between 0.57 and 0.75 (out of a possible 1.00 for optimal habitat). 6 out of 7 sites in the far-flung coastal area of Virginia Beach & Chesapeake met or exceeded that range. 0 out of 4 sites in the much closer interior flooded swamp (and rivers like the Nottoway) met that range, although 3 sites were close.
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A marketing analogy is easy - would you be more likely to drive 1 mile for a cheap, grizzly hamburger, or an unknown but longer distance to get a delicious steak dinner, cooked just the way you like it? That's exactly the type of decision that sub-adult male alligators are having to make when they get kicked out of their territory and consider a swim north.
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I'll polish up this analysis soon with some final predictions for where-exactly, and when-approximately, I believe alligators are likely to first naturally settle and reproduce in Virginia. As a teaser, here are the habitat suitability rankings of the wetlands I analyzed (this is assuming that alligators were air dropped on each site at the same time). Remember that I omitted 99% of the actual area of southeastern VA, concentrating only on "reasonably possible" habitats. These all represent marginal (ranks 14-8), good (ranks 7-2) , or near-optimal (#1) habitat.
19 - 15 Omitted
14. Impoundment at Cavalier WMA
13. Great Dismal Swamp @ Dismal Road
12. Mackay NWR Impoundments (NC)
11. Great Dismal Swamp (Lake Drummond)
10. Camp Mill Impoundments
9. Great Dismal Swamp (NC) (Existing gators - Reference Site)
8. North Landing River - lower reach
7. Aransas NWR Sloughs (TX) (Reference Site)
6. Northwest River - Hog Island (NC)
5. Northwest River - Irrigation Ponds
4. Merchants Millpond (NC) (Reference Site)
2. Ponds & marshes along the Albemarle & Chesapeake Canal
2. Large stormwater ponds along West Neck Ditch
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and the #1 ranked site is......