The Cricket Frogs
Genus Acris

Blanchard's Cricket Frog (Acris crepitans blanchardi)
There are three species of Cricket Frogs in the United States.  The Eastern Cricket Frog (Acris crepitans) is widespread in the eastern 1/3 of the US east of the Mississippi and Ohio Rivers, occurring from the Great Lakes to the Gulf Coast.  It is absent from New England and from peninsular Florida.

Known range of the Eastern Cricket Frog (Acris crepitans)

The Blanchard's Cricket Frog (Acris blanchardi) replaces the Eastern Cricket Frog west of the Mississippi and north of the Ohio Rivers.  It is physically identical to the Eastern Cricket Frog and is separated by its genetic distance and presumable some of the characteristics of its call.

Known Range of the Blanchard's Cricket Frog (Acris blanchardi)
In the southeast, there is a third species, the Southern Cricket Frog (Acris gryllus).  It differs from the Eastern Cricket Frog in aspects of its coloration and leg length as well as having a different call.

Known range of the Southern Cricket Frog (Acris gryllus)

All three species are highly variable and very difficult to distinguish without capturing them.  There is a difference in the relative length of the hind limb with the Southern, but this is impossible to determine without capturing the frog in areas where the ranges overlap.

Traditionally, there have two subspecies of Southern Cricket Frogs (Florida and Southern) and two subspecies of Northern Cricket Frog (Northern and Blanchard's).   Current taxonomy treats the Blanchard's Cricket Frog as a separate species.

Southern Cricket Frog (Acris gryllus)

Although these species are almost impossible to distinguish physically, there is a subtle but consistent difference in their calls.   Both species make a "click-click-click" call that has been likened to two pebbles being hit together.   At first, those two calls also sound very similar.  However, by listening carefully, you can learn to distinguish the two species.

Here is a recording of a "Blanchard's" Cricket Frog (Acris crepitans) from Texas.  Notice how "broad" the clicks are.  It sounds like someone hitting two stones together at a slight angle so that they are actually scraping against each other for a fraction of a second.

Contrast that call with the shorter, sharper clicks of the Southern Cricket Frog (A. gryllus), this time from Pasco County, Florida.  Once again, it sounds like two stones or marbles striking each other, but this time they are hitting straight on so the contact is shorter in duration.

The following recording contains a single typical "click" recording from a Northern and Southern Cricket Frog.  Each recording has been repeated 5 times so you can compare the length of each click.  The first 5 clicks are the Blanchard's Cricket Frog (A. crepitans) and the last five clicks are the Florida Cricket Frog (A. gryllus).

Notice that the call of the Northern/Blanchard's Cricket Frog is longer and more complex than the sharp click of the Southern Cricket Frog.

Here is a spectrogram comparing the two individual calls.  The first call is a single click from a Northern Cricket Frog (Acris crepitans/blanchardi) and the second is a single click from a Florida Cricket Frog (Acris gryllus dorsalis).  Both segments of the spectrogram represent the same time period (0.1 secoonds).  What you can see from the comparison is that although the clicks are superficially similar, the click of the Northern Cricket Frog is actually longer in duration.  The click of the Southern Cricket Frog is much shorter and sharper.

In some Northern Cricket Frogs, the clicks appear to be two separate sounds a few hundredths of a second apart.

© Chris Harrison 2012

No comments:

Post a Comment