Monday: 10 October 2011
Today and tomorrow are binary days - in YYMMDD format, 111010 and 111011. Next month we’ll have 111101, 111110, and 111111 and those will be the last binary days of the century.
Yesterday I predicted I wouldn’t find any box turtles, but the humidity was marginally good, the temperatures warm, and I found this fellow making his way across SBS Creek. He wasn’t happy to see me.
Perhaps it was because we’d never met before. He’s a new turtle, the fourth such in a row that I have found for the first time in the last few days.
And that brings up a new point - what is the probability that I would find four turtles in a row that were not turtles I’d seen before?
First, given the data since mid July of this year, I’ve reevaluated the mark and recapture results I wrote about at that time. At the time I estimated 40 turtles on the 20 acres under study. With the discoveries since then, I’d now up that to about 50 turtles, four or five of which are rediscoveries in the “recapture” period.
Second, in the last six years of observation, I’ve discovered 28 unique turtles. So the probability that the next turtle I’d find would be one I’ve found before would be 28/50 or about 56%. That means the probability that the next turtle I’d find would be a new one would be 100-56 = 44%. Finding four new turtles in a row is a probability of about (0.44)4, or 4%.
It depends on what you consider an acceptable probability but the most rigorous standards usually require a 5% cutoff to reject random coincidence. It just seems very unlikely that this could be a coincidence, everything being random (and I see no reason why it’s not).
One tentative explanation for this is that there are a lot of new turtles invading the study area, all of a sudden. This makes it much more likely that I’d pick up a new one rather than an old one.
It turns out that toward the end of the warm seasons, many box turtles will leave their summer residence (where I would not discover them during most of the turtle season) and return to their hibernacula, their winter residence which might not be the same place they spend most of the summer. The hypothesis here is that here in October is an influx of turtles that have spent May-September elsewhere, and are just coming home for a winter rest. I’m now finding them.
The hypothesis suggests a plan for a new census schedule, much more rigorous than the last few years when I’ve just been farting around. I’m thinking four periods of a week of daily searching. Two of these periods would be at the beginning and end of the season, and two would be in the middle. Next year would be my “capture and mark” year, and the following year would be my “recapture” year. The early spring and late fall periods would test the winter residents, and the two mid season periods would test the summer residents.
It looks like the weather is developing as planned , with rain just beginning and lasting through Wednesday, and warm temperatures continuing through the weekend. If so, I should be seeing more turtles on a daily sampling.