Whistling coqui on bromeliadPhoto William Stelzer.
Imagine young lovers calling out to each other in the darkening woods, looking forward to meeting up for a night of romance under the stars. Suddenly a bright light appears above them, which seems to be coming from the forehead of an enormous dark figure stalking noisily through the underbrush. As they hesitate, startled and confused, one of them is snatched up and carried off.
A short distance away the captive is poked and probed, and then something sharp snaps, taking off a couple of toes. The victim jumps and squirms and manages to escape – hopping off into the dark with an improbable tale about a frog-snatching, toe-biting monster lurking in the forest.
What sort of creature would do this?
It turns out to be a young woman wearing a miner’s light strapped to her head – Pearl Cales, one of the graduate students from the College of Staten Island in New York City doing research periodically at the Virgin Islands Environmental Resource Station (VIERS). She has been studying the frogs’ songs and calls, and also has a good eye for spotting them. She finds them hiding on low parts of trees in forested areas, inside bromeliad plants, or in the leaf litter on the ground. It takes quick hands to catch them.
Pearl Cales taking DNA sample from tree frog. Photo William Stelzer.
But why is she snipping their toes? Apparently it is difficult to identify the different types of native tree frogs just by their calls. The toe samples are used for DNA analysis.
The dominant type of frog on St. John is the Whistling Coqui (Eleutherodactylus cochranae), which is found only in Puerto Rico and the Virgin Islands. These frogs are quite small (about the size of a quarter) and are brown or gray with small brown spots on their throats and legs. They mostly sleep in bromeliads during the day and eat insects at night. They also lay their eggs in the bromeliads. The eggs hatch after about two days, without turning into tadpoles, so these frogs do not need to breed near a body of water.
The Red-Eyed Coqui (Eleutherodactylus antillensis) is a similar tree frog, also mostly found only in Puerto Rico and the Virgin Islands but not as common. In addition to its red eyes, it also has distinctive black streaks in front and back of its eyes. During the day, these frogs are generally hiding on the ground, but at night they get up on low bushes and branches to catch insects. After a rainstorm, the female will lay eggs in the wet leaf litter. These eggs too will hatch without any tadpole stage.
Unlike a coqui, the Caribbean White-lipped Frog (Leptodactylus albilabris) is semi-aquatic and needs to be close to water for breeding. The eggs are laid on the ground near a stream or a ditch suitable for tadpoles. Pearl found lots of these tadpoles in large puddles of water along the road by VIERS.
One of things Pearl is investigating is whether there are impacts on local frogs due to the introduction of three non-native species: the Puerto Rican Coqui, the Cuban Tree Frog, and the Cane Toad (Bufo marinus).
St. John is a small island and, as everyone knows, non-natives can be quite invasive, disrupting the domains and routines of the locals, and encroaching on or destroying their habitats.
Most people in St. John are already familiar with the Cuban frogs, which are much larger that the native ones. So far Pearl has not seen much impact from them on local St. John frogs, though in the British Virgin Islands coqui populations seem to be declining where Cuban frogs have spread into their customary habitats. (These big frogs can also cause lots of trouble for homeowners by squeezing into the water pipes – and even breeding in swimming pools).
Pearl Cales with Cuban Tree Frog. Photo Richard Veit
The even larger cane toads are of more concern. They have been showing up in Coral Bay, probably arriving in plants imported from Florida (like a number of other invasive species). These toads are voracious predators and will eat the native frogs, along with many other small creatures. (If threatened, they also produce a toxic secretion that can burn your skin and poison your pets.)
These introduced invaders seem to be the really dangerous coqui snatchers.
Cane toad. Photo Wikipedia
Here are some interesting links for learning about frogs and listening to their calls:
Different coqui frog calls: www.caribherp.org/index.php?il=Puerto_Rico-VI&fa=Eleutherodactylidae&vw=y&dd=n&so=sound&mob=y
Caribbean White-lipped Frog: www.youtube.com/watch?v=iWFYrSE_KqI