Early Summer Rains Bringing On Frog Calls

10 Jun 2020

Heavy rains brought about by Tropical Storm Cristobal started our wet season earlier than usual. Although the beginning of June is the official beginning of hurricane season and the wet season, in recent years we have not had as much accumulation of rain, from the normal rain pattern, until mid-to-late July. 

Early tropical storms that fill in ephemeral wetlands with water bring about mass amphibian reproduction, which in our case involves frogs and toads. Frogs congregate in these areas as males use their voice or frog calls to attract females in to breed. 

Like bird calls, frog calls among different species are unique and you can determine presence/absence and density of these species by being able to identify these calls. SCCF conducts frog call surveys on Sanibel over the summer to keep tabs on extant frog species and their abundances which helps us determine the health of wetlands.

Sanibel is home to nine species of frogs and toads with three of them being exotic species.

On most of the island, especially near the residential areas, the most commonly heard frogs over the summer after heavy rains are the exotic Cuban treefrog (Osteopilus septentrionalis) which sounds similar to rubbing your fingers down the side of an inflated balloon and the greenhouse frog (Eleutherodactylus planirostris) which is a subtle clicking sound that sounds like crickets.  

The large, Cuban treefrogs are often seen clinging to walls near lights at night and greenhouse frogs are very small frogs that are commonly found under debris outside homes such as pool equipment, toys, buckets, etc.

 As far as native species, if you live close to permanent to near-permanent water you will hear pig frogs (Lithobates grylio) which sound like a snorting pig or alligator usually in repetitions of three (er-er-er). The green treefrog (Hyla cinerea) and seldom heard squirrel treefrog (Hyla squirella), pictured below, are often called rain frogs in the south. 

They are both usually green and begin calling right before it starts raining. Their calls can be very loud in a chorus and sounds like “quonk-quonk or quank-quank” with the squirrel treefrog being raspier. The easiest frog to identify by sound is the little narrow-mouthed toad (Gastrophryne carolinensis), pictured below, which is not a toad at all, but a microhylid which is a family of very small frogs that can either be arboreal or terrestrial. Their obvious call resembles a sheep or lamb bleating (baaaahhh).

The two types of toads on the island, the native southern toad (Anaxyrus terrestris), pictured below, and the exotic cane toad (Rhinella marina) look very similar, especially as newly metamorphosed juveniles, but the cane toad gets much larger. The southern toad chorus sounds like a choir humming a high pitch extended note. The cane toad is similar but with a lower pitch and a percussive aspect to it, kind of like a 1950’s movie depiction of a UFO taking off.