Native Plants, Habitat Restoration, and Other Science Snippets from Athens, Georgia

Sunday: 26 May 2013

A Better Way  -  @ 17:55:55
A lot of my working efforts in the last few weeks have been in improving my system of box turtle surveillance, sampling, and measurements.

Surveillance and sampling: I've extended the study area to include the west ridge between the old and new properties, and the new property. I've been swingblading some trails into the new property floodplain, and circumnavigating it, so as to increase the ability to spot turtles in the thick ground vegetation. More about this later.

Measurements: I could kick myself for falling into the same old trap so many do - there's no point in starting something long term *now*, just because I didn't start it ten years ago. Although I've been observing turtles, first casually and then with more care, since 2005, I never bothered weighing them or measuring their dimensions. Once I never bothered, I continued to increasingly not bother.

Well, I finally remedied that. On the left, below, is a spring or hanging scale. I have a sock cradle that the hook grabs, and when I put a turtle in the cradle, the spring is pulled down along the calibrated scale, and I subtract the weight of the sock cradle from the total mass. This one measures up to 1 kilogram to 1 or 2% accuracy. So far the smallest turtle is 300 grams, and the largest is 440 g.

On the right is a pretty simple system for measuring length, width, and height. The ruler itself (lab techs will recognize the beloved Fisher six-inch plastic ruler) isn't enough, because the turtle isn't a regular polyhedron. It's hard to measure overall length for an irregular solid.

A lot of folks use vernier calipers for this, but I wasn't thrilled with the range of calipers I saw, nor the expense.

So I cut the stiff 4" wire rods from a plant flag we use to mark specimens in the field. To measure the turtle's length, I put him on the ground, and push into the ground one rod just ahead of his shell, and one just behind, both touching the shell. I do the same with two rods marking his sides at the point of greatest width. I then remove the turtle from his prison and measure between the rods.

On Thursday, after a very nice warm rain, I ran across Reuben and Ernest, both for the second time this year. These are two of the handsomest and most charismatic turtles I see. Normally they don't withdraw into their shells when I come across them, and actively continue to run off. They have to be considerably intimidated to get them to cooperate.

I remeasured them just to get a second set for accuracy and precision estimates, and then set them down next to each other.

It didn't take long before Ernest, above top right corner, emerged and started to walk away. As soon as he saw it, Reuben was in instant pursuit.

They ended up under a log, with Reuben on the left behind Ernest. A couple of hours later when I passed by going home, they were clearly in the process of mating.

The explanation as to why Ernest and Reuben would be mating is to be found here. Basically, Ernest is a female, one of the with just a hint of a plastron depression, so hard to be sure of. Our neighbors confirmed this with a photo of Ernest at their house making a nest a couple of years ago. I just never changed the name.

I expect the kids from Reuben and Ernest would be interesting to see, provided any survive.

Sunday: 5 May 2013

Where Are They Now?  -  @ 08:14:21
Last year on July 20, I found this small male turtle for the first time, paddling around in SBS Creek. On April 12 I found him again, 50 feet from his former spot and on the bank of the creek. He's the smallest young adult I've found so far. I'm guessing him to be around 10 years old. He's now called Napolean.

I've been doing a lot of walking this year, compared to last.

The figure at left shows red and green for trips I've taken; red for no turtles and green bars indicating the number of turtles on a given trip. So far, by May 2, I've walked 181 miles and have found 7 box turtles. Of course, 71 miles of the total was Jan/Feb when I found no box turtles, and had no expectation of it.

By this time last year, I'd found 11 turtles. That crude measure of activity is imroved by taking into account the time I'd spent searching for them, a metric I call "box turtle activity," in turtles/hour.

That measure of turtle activity is given in the figure you see below. You can see that April this year is only 1/3 of last year's activity.

The figure below is a 100-point running average of temperatures. This is a moving window of 5-7 days before and after the centered plot points. It smooths out the jags considerably, but also flattens out the actual temperatures to a longer term average.

I'm attributing box turtle activity in the early spring primarily to prevailing temperatures. We've been fairly normal this year, maybe slightly below normal (blue). Last year, though, we had the amazingly warm Month of March, followed by normal and greater than normal temperatures in April, seen here in red.

Going by temperatures, it seems that this April might be normal, and last April the activity was three times higher than normal.

If we go by precipitation, it would seem that box turtles don't like it wet, which I think unlikely. By this time last year we had 9" rainfall, 50% of a normal 18" by May 1. This year we're above normal with 20". It is true though that our warmest March and April days have also been our driest, with cooler than permissible temperatures following periods of rain. So it's complicated by that pattern.

Trying to figure out box turtle emergent behavior in the volatile spring isn't a fool's errand, but it is perplexing. I've even attributed it to not wanting to get out of bed until breakfast is ready. In the end, the box turtles will emerge for good when they want to.

Friday: 3 May 2013

The Month of April  -  @ 12:53:04
It's The Month of April, Number 87 in a series. For us in northeast Georgia, it was a perfectly average April. And I mean average - chi squares were the smallest evah!

Here are the usual temperature anomalies products, at the National Weather Service Climate Prediction Center. Displayed is the mean temperature anomaly. Click on it and you'll get the high and low temperature anomalies on a new page.

Much of the US, especially the Midwest extending south, continued under much colder than normal conditions. The region of unusual warmth in the West shrunk into the southwestern corner of the country. The eastern US warmed just slightly above normal

We find the National Weather Service Climate Prediction Center's precipitation plots here.

The dry conditions of February and March continued in the West, as did the average to above average precipitation seen in the central and eastern US. Most regions in Florida got at least normal rainfall, but the coastal New England states were drier than normal.

For the Athens, GA area:

Here is a plot of our daily temperatures excursions in April, along with precipitation amounts as experienced in Wolfskin. In December and January we had higher than normal temperatures; in February we returned to seasonably cold weather. Cold weather intensified in March, with the average temperature much below normal for much of the month. April returned us to average temperatures. Rainfall was unusually heterogeneous across the Athens area, in April.

The average monthly temperature for April was 61.2 degF, just about average. We had 6 day more than 1 standard deviation above normal highs (4.9 normal), and that was balanced off by 5 nights more than 1 standard deviation below normal lows (5.4 normal). We broke no records. While there were some swings in the daily highs and lows, it all averaged out.

The monthly histogram below shows the breakdown of high and low temperature range counts from April 1948 on. The error bars are just plus/minus one standard deviation, which I arbitrarily set as the limits outside of which are "significantly" anomalous.

You really couldn't get much closer to the average in any of the temperatures ranges.

The figure below shows the Athens precipitation data which are official for our area. As usual the green line shows our actual rainfall, the red shows the average accumulation expected. The black dots are rainfall over the last 22 years, and the river of peach shows the standard deviation.

Our total out here was 3.11", and the official recording in Athens (shown here) was 3.77". 3.15" is normal for April, where we ended up out here. But rainfall was very different for locations not that far apart - it ranged from 2.5" to nearly 5" for CoCoRaHS observers in Clarke and Oglethorpe counties.

Prognosticator stuff:

What is the neat prognosticator telling us? A considerable turnabout in terms of both precipitation and temperatures - the next month will be cooler and wetter, grading to normal for us in northeast Georgia. The overall three month picture through July is for above normal temperatures for much of the US, excepting the northernmost tier of states and the Pacific states. This is countered by normal rainfall for the first half of the summer, except for a swath from Washington southeast to Texas.

ENSO stuff:

The folks at CPC have a version of PDF or HTML that is much different from their previous presentations, but at least it's there and the link isn't broken.

As of April 29, ENSO neutral conditions continue, and are expected to remain neutral into the Northern Hemisphere summer. We've remained ENSO neutral now for over a year. The last such lengthy period was 10 years ago, 2003-2004.

NOAA's Monthly State of the Climate product for March is available. And last year's annual report for 2012 regionally, nationally, and globally is also available.

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