OK, so this blog post is going to start off with a correction to a previous blog post. My previous blog post about the Cane Toad (Rhinella marina) discussed the Cane Toad as being a species native to Texas, Mexico, Central America, South America and introduced to a variety of places worldwide. But a recent study based on mtDNA and skull morphology has shown that this "species" is actually two species of toad! So I am changing my old blog record to cover Rhinella marina and will make a new post for the Texas species, Rhinella horribilis. The Giant Toad (Rhinella horribilis) is a massive toad occuring from South Texas down into Mexico, Central America and along the northwest coast of South America (west of the Andes).
Giant Toad (Rhinella horribilis) Costa Rica
In Texas, this species is restricted to the lower Rio Grande Valley, occurring along the river and inland from Laredo down to the mouth of the Rio Grande. In South Texas it is a fairly common species.
Adult Cane Toad Chiapas, Mexico
These are massive toads. Adults have exceeded 5 pounds in mass and been over 15 inches long.
The call of the Giant Toad is actually what you would expect for a huge toad. Toads generally have trilled calls. Smaller toads have faster, high-pitched trills and big toads have slower, low-pitched trills. The bigger the toad the lower pitched the trill. The trill of the Giant Toad is so slow and low pitched that it is drum-like. This individual was from north of Aguas Zarcas, Costa Rica.
Here's a slightly longer section of call from an individual near Caño Negro, Costa Rica.
For newcomers to frog calls, one of the first problems to be faced is how to know if the sound you are hearing is actually a frog or a bird or an insect or a distant car alarm, etc..
In general, I have found that most frog and bird calls are pretty easy to distinguish if you know what to listen for. Generally bird calls are short and often variable. Birds may repeat the same call but they will often do so in short bursts. They rarely have a very long call for the simple reason that their metabolic rates are higher than amphibians and so they need to breathe more often. Frogs and Toads can call longer. Another difference I find is that bird calls are more variable. Birds don't necessarily repeat the exact same "phrase" over and over again. They can, but they often vary them a bit. Frogs and Toads tend to stick to one call and repeat it over and over. Frogs and Toads can have more than one call or "ramp up" to their main calls, but they generally have a recognizable pattern that is repeated. Frogs and Toads are more likely to call in constant choruses as well. Furthermore, Frogs and Toads will call in the day or night whereas most birds will restrict their calls to a particular period of daily activity. Of course, there rules are made to be broken. Last year, I was listening to some bird calls online at that wonderful repository of online bird calls, Xeno-Canto.org. I was trying to find a call of the Lesser Nighthawk, a crepuscular/nocturnal bird that occurs in my area during the summer and active frog breeding seasons. I was quite surprised when I heard some of the recordings because I realized that if I had heard those recordings in the field, I would certainly have been likely to assume they were the Giant Toad (Rhinella horribilis).* The Lesser Nighthawk (Chordeiles acutipennis) is a "goatsucker" in the bird family Caprimulgidae along with more familiar birds like the Eastern Whip-poor-Will and Chuck-will's-widow. Lesser Nighthawks are crepuscular aerialists that fly erratically in the evening skies catching insects on the wing. During they day, they generally sit motionless on the ground or along a tree limb hoping to go unnoticed due to their camouflaged patterns.
Lesser Nighthawk (Chordeiles acutipennis)
Port Aransas, Texas
While some species of Caprimulgids are noisy, the Lesser Nighthawk is generally fairly quiet. However it does have a long trilled call and it is this call which is reminiscent of the Giant Toad in many aspects. To confound the issue, the Giant Toad and Lesser Nighthawk have a very similar range and would be actively calling at the same times of day.
Here is a recording of a Lesser Nighthawk from Xeno-Canto.org. This recording was made in Southern California by Lance A.M. Benner.
I have copied the preceding recording in its entirety to my website under the terms of the Creative Commons License that applies to Xeno-Canto calls. This call can be seen directly from the Xeno-Canto website at http://www.xeno-canto.org/176666.
Although a Giant Toad (Rhinella horribilis) doesn't look much like a Lesser Nighthawk, their calls are surprisingly similar.
Here is a recording of a Giant Toad from Costa Rica for comparison. Of course the length and volume of the overall call may vary, the general sound is very similar to my ear.
Here's a call from an individual near Caño Negro, Costa Rica.
Here is a few seconds of the Lesser Nighthawk followed by a few seconds of Giant Toad -
So it is worth listening carefully if you think you hear a Lesser Nighthawk or Giant Toad trilling in the scrubby areas of Central or South America. You might be calling one species the other?
My thanks to Lance Benner for letting me use his Lesser Nighthawk recording for this comparison.
