Agalychnis spurrelli

It would truly be an understatement to say that the Gliding Leaf Frog is a rare find in Drake Bay. It was not collected in Costa Rica until 1967 and until recently was only thought to exist in the southern Pacific region of the country. They are, however, also found on the southern Caribbean Slopes of Costa Rica.

It was a misty night in late July that we discovered our first Gliding Leaf Frog. As we walked down the trail just past La Paloma Lodge, the silhouette of a tree frog perched on a leaf caught the corner of my eye. The frog was off the trail on a leaf about two meters off the ground.

We were having a great frog night, and I nearly passed it by thinking it was a Masked Tree Frog (Smilisca phaeota) or a Gaudy Leaf Frog (Agalychnis callidryas), both of which we had already seen. I decided to have a look anyway and approached the frog, convinced it was a Gaudy Leaf Frog the closer I got. As I took it in my hand, it surprised me by letting out a deep, baritone "Grrrrt!". I could not believe my eyes as I inspected the beautiful frog and realized it was a Gliding Leaf Frog. Knowing what we had, Tracie and I were by far the most excited people in the group that night. The frogs featured on this page are those two wild individuals encountered in Drake Bay during the Night Tour.

Gliding Leaf Frogs are the largest members of their subfamily (Phyllomedusinae) in Costa Rica, with adults measuring between 67 and 95 millimeters. Frogs on the Pacific side are slightly smaller than on the Caribbean and also differ in that their belly has an yellowish-orange coloration. They are similar in appearance to the Gaudy Leaf Frog (Agalychnis callidryas), to which they are closely related. At first glance, one striking difference is their huge, highly webbed hands and feet as well as the yellowish-orange coloration covering their hands, feet, belly, and sides.

They are strictly canopy dwellers, which explains why they are so rarely encountered in their forest habitat. Their common name is derived from a very peculiar mode of locomotion they employ. When these frogs are in a hurry to get down to the ground or are fleeing from a predator, they will freefall from their treetop perch. As they fall, they will spread their extensively webbed fingers and toes, breaking their fall. Studies have shown that frogs released at a height of 4.5 meters achieved nearly a 45 degree angle of descent and traveled up to 4 horizontal meters during their fall!

Gliding Tree Frogs are nocturnal and normally only descend to ground level during their mating season. At this time, large congregations of frogs gather at temporary ponds, flooded with rainwater. Gatherings can number into the thousands and huge numbers of frogs are literally draped throughout the vegetation from 1.5 up to 10 meters above the water. This usually takes place during or after a heavy rain. Breeding starts at night, but will sometimes continue until direct sunlight reaches the breeding area, the next morning.

A few of our friends guiding in Corcovado National Park have been lucky enough come across these incredible scenes. To their bewilderment, entire trees are swarming with thousands of mating frogs, their branches bending under their weight and their leaves overwhelmed with egg masses.

Once daylight crashes the party, the frogs disappear into the canopy just as quickly and suddenly as they emerge. Just as we have a few friends who have witnessed these amazing reunions, we have other friends who have been guiding in the area for decades and have never seen a single Gliding Tree Frog.

The egg masses are laid on the upper surface of leaves and normally contain between 14 and 67 eggs. They will develop on the leaf for about six days until the tadpoles wiggle out of the egg mass and into the water below. This will be their home for the next two to three months until their metamorphosis is complete and the little tree froglets leave the water to continue their lives in the forest canopy.

Gliding Tree Frogs are only know to exist in Costa Rica, Panama and Northwestern Ecuador. 

References:

Kubicki, B.  2004  Leaf-frogs of Costa Rica  Editorial INBio

Savage, J.  2002  The Amphibians and Reptiles of Costa Rica   University of Chicago Press