Thursday, September 19, 2013

Why do turtles bask?

 Redneck, my favorite Red-eared Slider Turtle (Trachemys scripta elegans) is spending a lot more time basking than he did earlier this summer.
 There are a number of reasons that turtles bask.  The primary reason for turtle basking is that basking strengthens the shell and reduces algae growth on the shell.  A clean healthy shell is less susceptible to bacterial and fungal infections.
 In these photos Redneck basks on the side walk around our 5,000 gallon pond (the Big Pond; 19,000 liters).  He has been spending almost all his time in or around the Big Pond, presumably because this is where he is planning to overwinter.  It is now mid-September and while the temperatures remain in the 90°s F (34° C) the days are getting shorter and the turtle has evolved an understanding of the changing seasons.
These reptiles do not hibernate.  Instead they brumate, becoming less active, but occasionally rising for food or air.  Red-eared sliders brumate over the winter at the bottom of ponds or shallow lakes;  they become inactive, generally, in October, when temperatures fall below 50° F (10° C).  We have many weeks before nighttime temperatures drop into the 50°s at this latitude (maybe late November?).
 During warm periods in winter the turtles will rise to the surface and bask anew, only to return to the bottom of ponds when temperatures drop.  During brumation, Redneck will survive for weeks, producing ATP from glycolysis (essentially living off of his stored fat).  His metabolic rate will drop dramatically, with heart rate and cardiac output dropping by 80% to minimize energy requirements.  Lactic acid produced while he's subsisting underwater will be buffered by minerals in his shell, preventing acidosis.
I've noticed that Redneck is staying at the farthest end of the Big Pond and doesn't respond to my calls some days.  I suspect this is the beginning of his transition into brumation.

Redneck, nor any of our other turtles, are able to leave the area for larger, more natural ponds as everything is dry from the persistent drought affecting east central Florida.  The 700 acre lake behind our property remains mostly dry.

Turtle Joke

At a public lecture, a scientist explains the earth's orbit around the sun, and the sun's around the galaxy.

"That's wrong," a woman in the audience says, "The earth is a flat plate resting on a turtle's back."

"What's the turtle standing on?" the scientist asks.

She replies, "It's turtles all the way down."

There is a lot of other activity around our ponds which I keep hydrated despite the dry weather.  Above:  An Eastern Pondhawk Dragonfly's eyes glow green in the camera's flash.  Also known as Erythemis simplicicollis, these dragonflies are abundant this season.

Native to the eastern two-thirds of the USA and southern Ontario, Canada, this species of dragonfly is distinguished in that the female is bright green and the adult male has a blue abdomen with a green face and green and blue thorax.  I'd guess this one is a male.

One of our two Red-tailed hawks (Buteo jamaicensis) sits atop the swing annoying all the animals in the garden.   This was a pretty good shot considering that I took it through two sets of screens and a dirty glass door. . . some testament to the ability of the latest generations of digital cameras to compensate for bad photography.  The other of this pair of Red-tailed haws is pictured at this link.
 A family of raccoons has a burrow behind the first pond.  This too might be why Redneck has been staying away from this more shallow pond.  The juvenile raccoons can see me even through screen and glass and are very shy.
 Below:  Most of my photos of the raccoons moving in and out of their burrow come out looking something like this (blurry).  Because of their timidity I do not see them emerge from the burrow unless I go inside the house.
 As the days get shorter the sky becomes more interesting.  Notice how there are absolutely no clouds in the late evening sky.  Very unusual weather for the peak of hurricane season in Florida.  A couple of days ago the crescent moon and venus were visible almost together in the western sky at sunset.

This particularly uneventful hurricane season and the persistent dry air is being partly blamed on the historic drought ongoing in Brazil.  Whatever it is, we'd be happy to have a few rainy weeks.