Black Bear Vehicle Strikes

A few weeks ago I wrote a piece on the Florida black bear hunt of 2015. I want to revisit that discussion with some new data that I've been able to find. To refresh, the small sizes of the bears in the northern 3 BMU's relative to the South BMU led me to think that there was a need for the bear hunt to control the population. The small sizes stemmed from a lack of food and a healthier population would be seen if it was smaller relative to the current food supply.

Bear in Woods

Here's a map of the 4 BMU's that had a bear hunting season in 2015:

Florida Bear Management Units

But with statistics there are always questions. All of the bear hunt data is collected in a couple of days. Would the earlier conclusions hold up if we look at bear deaths over a longer period of time?

Today I wanted to look at the data on bears that are struck by cars in Florida. Here's my thought: Maybe some of the information that I found was somewhat self selected. Maybe there's a reason I don't understand for the very small bears in the North Florida compared to the larger ones in the South Florida.

I decided I may be able to get information from the roadkill data. Every year in Florida a large number of bears are killed as a result of car strikes. Would that confirm my hypothesis that the bears in South Florida are larger?

Average Roadkill Bear Weight, 2014-2015

So here's a chart of all car strikes in Florida for 2014 and 2015. A couple of thoughts:

1> The bears here are smaller than the bears in the hunt data. That probably says that the hunters were staying away from the cubs during the hunt. However cars aren't able to avoid them as easily.

2> Overall the size ratios are about what I'd expect with the males being larger in 3 of the 4 BMU's. Only the North has larger females than males and this may be just a function random variation due to fewer data points in the north.

And speaking of few data points in the north here are the total bears killed by cars in the 4 BMU's with a significant bear population:

Roadkill Bears, 2014-2015

Interestingly the Central BMU has roughly the same bear population as the South BMU but has over 5 times as many car strikes. That's probably just a geographic feature. Bears in the South BMU are congregated around the Big Cypress area, a relatively unpopulated part of Florida. In the Central BMU they're found in more fragmented habitat and mixed in the human population much more. 

So, overall I went looking for confirmation that the bears in the northern BMU's were not getting enough food. I found some confirmation in the overall sizes but the smaller number in the roadkill data made for more variation in the numbers. Ah, the life of a statistician -- each new data point brings more questions.

I've just gotten my hands on some hunt data for 2015 from South Georgia that should shed some additional light on the subject. Stay tuned.