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Eleutherodactlyus marnockii vs. E. cystignathoides

Posted: May 10th, 2012, 9:01 pm
by chrish
I live in an area occupied by two species of Chirping Frogs (Eleutherodactylus) - the introduced Rio Grande Chirping Frog (E. cystignathoides) from the lower valley and the native hill country Cliff Chirping Frog (E. marnockii).

When you see these two species, they are easy to tell apart as E. marnockii is at least 2-3 times the size of E. cystignathoides.

Token photos -

E. marnockii - rocky, hill country canyons

Image

E. cystignathoides - usually a suburban backyard frog (but spreading rapidly)

Image


The problem is that I often record vouchers for NAHerp of calling frogs and there have been a few cases where I was in habitat that suggested E. marnockii, but close enough to a residential area to make me suspect E. cystignathoides.

So I set out this summer to record both and figure out the difference. In case you care, here's what I learned.

Both species have two "types" of calls. More complex trill like calls which are easy to tell apart and their single chirp note calls which sound almost the same to me.

So I recorded some known individuals and compared their calls and spectra of those chirps, and here's what I learned.

I cut and pasted a series of chirp calls from different frogs and different localities (and different dates) in the following order. See if you can hear the difference. The order is

marnockii - 6 chirps
cystignathoides - 4 chirps
marnockii - 1 chirp
cystignathoides - 6 chirps
cystignathoidess - 4 chirps
marnockii - 4 chirps (with crickets)

Click this link to hear the call comparison.


The difference is obvious when you hear them together. The question is can I learn to distinguish when I only hear one species?

If you look at the spectra for this recording, you can see the difference. E. marnockii's calls are all right around 2000-2500 khz while E. cystignathoides range from 2500 - 4000 khz.

Image

(In case you care and aren't used to reading spectra, the small vertical bars labeled represent the chirps and the Y axis is the frequency (pitch) in khz. The bars for the E. marnockii calls are lower than the E. cystignathoides calls because the call is lower in pitch. The X axis is time. Play the recording again and watch the spectra, counting the chips as they call.)

I doubt I will ever learn to distinguish whether the call was above or below 2500 khz, but I can always check the spectra if I record it I guess.

Anyway, just thought it was interesting. Another herp ID tool for me at least.

In case anyone cares, all the cut-and-paste recording and the spectrum were produced in the free (and awesome) audio program Audacity.

Chris

Re: Eleutherodactlyus marnockii vs. E. cystignathoides

Posted: May 11th, 2012, 12:57 pm
by Tom Lott
Chrish,

As one of the other handful of people who are interested in this topic, thanks for taking the time to put this together. I have been working on this also with another sound analysis program, but my results haven't been as illustrative as yours.

I still don't completely trust my ability to aurally distinguish between the two when I hear only a single calling individual in an area where either may occur. I have always personally characterized the call of marnockii as a bit softer than cystignathoides, with the chirps sounding somewhat like drops of water.

Additionally, one would think that there are probably some hybrids out there in such areas of sympatry as you mentioned, along with places like Brackenridge and Olmos Parks in San Antonio, where marnockii occurs completely surrounded by cystignathoides.

Tom Lott

Re: Eleutherodactlyus marnockii vs. E. cystignathoides

Posted: May 11th, 2012, 2:31 pm
by chrish
Tom Lott wrote:Chrish,

As one of the other handful of people who are interested in this topic, thanks for taking the time to put this together. I have been working on this also with another sound analysis program, but my results haven't been as illustrative as yours.

I still don't completely trust my ability to aurally distinguish between the two when I hear only a single calling individual in an area where either may occur. I have always personally characterized the call of marnockii as a bit softer than cystignathoides, with the chirps sounding somewhat like drops of water.

Additionally, one would think that there are probably some hybrids out there in such areas of sympatry as you mentioned, along with places like Brackenridge and Olmos Parks in San Antonio, where marnockii occurs completely surrounded by cystignathoides.

Tom Lott
I'm headed out tonight to an area that should have marnockii and which received a lot of rain yesterday. I hope to get some more Chirper calls to analyze and hopefully be able to lay eyes on the vocalists (tough with Eleutherodactylus in general). (EDIT - not a single chirping frog calling where I went. :( . Lots of frogs, just no chirpers)

I don't know if the two could hybridize due to the size difference between the adults, but I'm not sure. I don't even know if they have the same number of chromosomes?

As for programs, Audacity is pretty good for a free program. I have used Raven as well which is also available free and supposedly more sophisticated, but I find Audacity works great for me and is easier to use in its free version.

Re: Eleutherodactlyus marnockii vs. E. cystignathoides

Posted: May 14th, 2012, 7:30 am
by Gluesenkamp
Great information. Thanks for posting.
Andy

Re: Eleutherodactlyus marnockii vs. E. cystignathoides

Posted: May 22nd, 2012, 11:10 am
by Reptiluvr
This was a very cool post. This is the first time I have ever visited the S Central Chapter board too. Very cool that you put in this much work and showed it to us. Not that I plan to ever be in the area, but maybe now I could distinguish the two by sight and sound.

Re: Eleutherodactlyus marnockii vs. E. cystignathoides

Posted: May 25th, 2012, 5:15 pm
by Mike VanValen
Nice post and something a little different than the usual stuff. :beer: