Phenology: Crooning Frogs and Perilous Chelonians

Yesterday (March 13, 2012) marked the first day of the year where I heard a full-blown caucophony of Chorus Frogs (Pseudacris triseriata).  They were calling heavily in the wetland near campus, and they have an unmistakable call (often likened to the sound produced from running one's fingers up the teeth of a metal comb).  They are one of the first, if not the first, species to call here in the spring.  The males have migrated down to the ponds and wetlands from their overwintering locations and began making that melodious advertisement....in the hopes of attracting a mate. 

Soon to follow should be the Wood Frogs (Rana=Lithobates sylvatica), the Northern Leopard Frogs (Rana=Lithobates pipiens) and the Spring Peepers (Pseudacris crucifer).  In fact, in some locations, the Wood Frogs and Peepers will start first or at the same time as the Chorus Frogs.

In general, I'd say these Chorus frogs are calling earlier than I've heard in past years 'round these parts.  Looking back at my field notes, I have the following dates of when I first heard these fellas....

2001: April 14th
2002: April 6th
2004: March 28th
2005: April 7th
2006: April 12th
2007: April 27th
2008: April 8th
2009: April 14th

For the last two years, we've lived out of state, so I didn't get the dates when these critters were first heard calling.

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One of the roads I follow when I head to work runs parallel to a creek for a ways (on the east side of the road).  On the west side of this same road is a large grassy hill and beyond that, a shallow wetland.  Last fall, it didn't take long to realize (after observing numerous turtles on the road.....alive or otherwise) that the wetland was a good summer habitat, but come winter....it was better to be somewhere else.

Why?

That shallow wetland is very likely to freeze solid during the cold winter months.  This isn't good news for an overwintering turtle (i.e., you can only burrow down so far in the sediments to escape from freezing solid).  You also likely have to deal with anoxic conditions, or very low oxygen levels, in wetlands that are completely covered in ice (i.e. no oxygen exchange between the surface of the water and the air).  Some species are particularly good at dealing with anoxic conditions in the winter (see Ultsch and Reese, 2008 for information on the Common Snapping Turtle; Chelydra serpentina).  But, if the option exists to avoid freezing and anoxic conditions in the winter.....if you're a turtle....I suppose there's no reason not to jump at it!

Thus, fall migrations to a flowing stream, which has a low potential for freezing solid and likely high oxygen content in the water, makes perfect sense.  It also makes sense to hang out in the wetland during the summer.  High nutrient levels and warmer water usually mean wetlands are very productive habitats (i.e., food is plentiful!).  So...come spring, you crawl out of the stream and start the treacherous journey back to the wetland. 

Yet....what happens when a road exists between your winter habitat and your spring/summer habitat?  Well, you try and cross it.  For a slow-moving turtle, this is a difficult task.  So difficult, in fact, that many do not survive.

Today marked the first day of spring that I found a Painted Turtle (Chrysemys picta) trying to cross this road (heading east to west, from the stream to the wetland).  Luckily, I caught him at the beginning of his journey and was able to pull over, pick him up and help him across the dangerous part.

Amazingly, the picture I snapped before picking him up also happened to perfectly capture the turtle's primary antagonist when crossing these roads.

More to come!

Literature Cited:

Ultsch, G.R, and S.A. Reese. 2008. Ecology and Physiology of Overwintering. In Steyermark et al. (eds.) Biology of the Snapping Turtle (Chelydra serpentina). John Hopkins University Press.

There is a wealth of literature on the impacts that roads have on turtles.  The following is a great place to start.

Andrews, K.M., J.W. Gibbons, and D.M. Jochimsen. 2008. Ecological effects of roads on amphibians and reptiles: a literature review. In Mitchell, J.C. et al. (eds.). Urban Herpetology, Herpetological Conservation No. 3. Soceity for the Study of Amphibians and Reptiles.