The Túngara Frog (Engystomops pustulosus) is a fascinating little frog from the family Leptodactylidae (the "Southern" Frogs). They range from tropical parts of southern Mexico all the way south into northern South America. They are small "warty" frogs that remind me more of a toad than a member of the Leptodactylidae.
This frog is one of the foam nest breeding frogs. The adult males whip up a nest of foamy material from their backs and the material surrounding the eggs. The eggs then float in this foam nest until the babies hatch and swim down into the water. This prevents fish and other aquatic predators from preying on the defenseless eggs. They call and breed in ponds, roadside ditches, flooded grasslands, etc.
These little guys that I recorded were calling from a narrow, shallow muddy roadside ditch that was only a foot wide and maybe two inches deep. It had rained heavily earlier in the day and these guys were calling from this ditch right in front of a noisy local bar. I wonder if the loud music of the bar interfered with their chances of attracting "the ladies"?
The call of the Túngara Frog seems totally out of character to their size and shape. You don't have to be a frog fanatic to love the call of this little species! It sounds like a ray-gun sound effect from a cheap science fiction movie. It is a loud descending "peuuww" that carries long distances. The end of the call is often punctuated with short buzzy "dit-dit" or "dit-dit-dit". So the whole call sounds like "peuuuw-dit-dit". The little "dit-dit" at the end of the call apparently makes them more attractive to females.
Looking at the spectrogram here you can see the descending nature of the "peuuuw" followed by the abrupt "dit-dit".
The calls of these frogs have been intensely studied. One aspect that has been well studied is the way certain predatory bats use these calls to find these frogs and prey on them. Research has shown that the extra "chucks" (my "dit-dit") added to the calls increase the response of females, but also make it easier for the bats to track down the ripples on the water produced by these sharp sounds. But evolution has led to an interesting arms race between the frogs and the bats and the frogs are capable of modifying their calls to reduce the chance of attracting predatory bats.
Other studies of these frogs calls have looked at the complexity of the female's mate choice decisions based on variation in the calls of the males. There's just a lot of people interested in these little frogs! I'll put a few of the published studies below, but there's a lot more of them if you look around the web.
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© Chris Harrison 2023
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