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
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.
Giant Toad call from 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?
© Chris Harrison 2015