Dendropsophus ebraccatus

Hourglass Tree Frogs are one of Costa Rica's most sought after frogs by nature photographers. They simply make great subjects. With their blend of coppery orange and golden yellow, these beautiful little frogs are true jungle gems.

Their common name comes from the hourglass shaped pattern which is usually present on the frog's back, as can be seen below. The pattern could also be described, perhaps more accurately, as the portrait of a sitting cat. Their arms and legs are normally boldly patterned, but their thighs are always a solid yellow color. This explains the species name, ebraccata, which in Latin means "without trousers".

Hourglass Tree Frogs are small frogs, with adult females measuring 35 millimeters at their largest and adult males only 27 millimeters. They inhabit the humid lowlands on the Caribbean and Pacific slopes of Costa Rica and are apparently absent from the drier Guanacaste Province in the northwest of the country.

They spend the dry season in the forest canopy, and two individuals were once collected from a bromeliad about thirty meters above the forest floor! Once the rainy season begins, Hourglass Tree Frogs descend to temporary ponds which have flooded with rain water.

Males will generally space themselves about a meter apart and call from vegetation near the pond, usually overhanging the water. Calling usually takes place throughout the night. Their call is a very loud, harsh "creek, creek". It serves both as an advertising call, intended to attract a female, and as a territorial call, intended to keep rival males at a distance.

Sometime during the evening, a gravid female will approach the breeding site. She may sit and listen for up to three hours until she decides on which male she likes. She will make this decision based solely on his call. At this point she will make her way towards her chosen mate, perhaps passing several other calling males along the way.

Although she has already made up her mind on her future mate, competing male frogs are not so easily deterred. Invasive male frogs will often try to intercept a passing female and position themselves on her back, in mating position. If this occurs, females will generally struggle to free themselves. One such case was observed where a female was squeezing through a tiny gap between a fallen branch and the ground, knocking off her assailant in the process!

Once a female is finally in close proximity of her chosen mate, she will turn her body sideways and waits until the male climbs onto her back and clings to her near the base of her arms. This position is called axillary amplexus and can be observed in the photograph on the left.

She will then make her way through the vegetation, with the male clasped on her back, until she reaches a suitable spot to lay her eggs. This is normally on the top side of a leaf overhanging the temporary pond. Egg clutch sizes may vary from 15 to 296 eggs.

The eggs will develop on the leaf until the little tadpoles wiggle out of the jelly mass and fall into the water. They will develop in the temporary pond for another four to six weeks, when the little tree froglets complete their metamorphosis and leave their watery home to take up residence in the trees. Hourglass Tree Frogs range from Southern Mexico to Western Colombia.

References:

Leenders, T.  2001 

A Guide to Amphibians and Reptiles of Costa Rica  Zona Tropical

Savage, J.  2002 

The Amphibians and Reptiles of Costa Rica   University of Chicago Press