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Rainforests of the World 

October 12, 2010

In the Field: Poison Frogs

This August several Academy biologists, Brian Freiermuth, Victoria McCloskey, Nicole Chaney and Chief of Public Engagement, Chris Andrews, went to Costa Rica. An important outcome of the trip was bringing animals back for our exhibits. However, trips like this are beneficial to staff for a reason even more important than the individual animals they bring back: these trips allow staff to view how the animals behave in the wild. They give the biologist first hand knowledge about the animals he or she studies or takes care of. It is one thing to read about another person’s experiences with an animal in captivity or even in the wild. It is an entirely different and somehow more genuine experience to find animals and plants where they have evolved, where they persist, where they live.
This post is about our experiences with one very popular group of frogs, the poison frogs and how our experiences in the field may lead us to be better caregivers for our frogs at the Academy.
When many people think about poison frogs they think of bright colors and boldness due to the protection given by the poisons these colors advertise. These descriptions are not always wrong, but they are not entirely correct either. While poison frogs are brightly colored in many cases, there are many cases where the bright color of the species is limited to a few streaks of bright coloration or missing all together. This is true of Costa Rica’s representatives from the genus Phyllobates. While the Phyllobates of Columbia may be solid mint green, solid yellow or even orange, the Costa Rican varieties have thin yellow stripes or orange stripes on black backgrounds. These frogs are often on the ground and when startled, they propel themselves into cracks or deep into holes. They do not just sit out and dare predators (or rather slow handed biologists) to grab them up. When startled, they behave like most animals, they move quickly to a safe spot and wait the danger out.

Dendrobatidae

Photo copyright of: Brian Freiermuth

The term Poison Dart Frog is somewhat a misnomer. The name is often used to call out all the colorful frogs in the family Dendrobatidae. However, only three frogs in the entire family are really used to make darts poisonous. This species, Phyllobates lugubris is a member of the genus that contains these three species. However, there is no evidence that P. lugubris has been used by indigenous people for the purpose of increasing the lethality of projectiles.

Phyllobates terriblis

Photo copyright of: Brian Freiermuth

The brightly colored Phyllobates terriblis, regarded by many to be the world’s most poisonous animal, is in the same genus as some of the frogs we saw but is found in Columbia, not Costa Rica.

Phyllobates vitattus

Photo copyright of: Brian Freiermuth

Phyllobates vitattus is found on the western side of Costa Rica.

Possibly the most emblematic of the Costa Rican poison frogs is the strawberry poison frog, Oophaga pumilio. This species has an extremely interesting life cycle wherein the mother of a tadpole brings food in the form of unfertilized eggs to the water vessel where the tadpole lives. In captivity, nobody has been successful in rearing baby strawberry poison frogs on a diet other than frog eggs. Additionally, some forms of these frogs (there are many color varieties which are sometimes associated with a geographic locality) are viewed as difficult to breed. While some forms are rare in captivity, this frog is far from a rare denizen of the deep primary forest. It is extremely abundant where it occurs and is and is more common in fairly disturbed areas than in pristine ones. We found dozens of them in a small area, in a brief amount of time. It was striking how many there were and where they were. I had the best luck finding them in a poorly maintained banana field and around stands of introduced bamboo. It is common dogma that this species requires bromeliads to complete its life cycle. In reality, these frogs will use a variety of water holding plants to reproduce. It is very likely that any small water body will be sufficient. In the localities where we found these frogs there were very few bromeliads.

Oophaga pumilio 'blue jeans'

Photo copyright of: Brian Freiermuth

The blue jeans form of the strawberry poison frog is common where it occurs. Many people who keep this frog in captivity find that this form is more challenging than other forms of strawberry poison frogs.

Oophaga pumilio 'red form'

Photo copyright of: Brian Freiermuth

The red form of strawberry poison frog was abundant in degraded habitats.

Oophaga pumilio

Photo copyright of: Chris Andrews

In less than an hour our group had captured about 40 strawberry poison frogs in one locality. Most of the frogs were female. We sorted through the group and selected six: three males and three females for transport back to the Academy.

The granular poison frog, Oophaga granulifera, is another poison frog that feeds its tadpoles eggs. This species is found on the west coast of Costa Rica and was also not uncommon, though not nearly as common as the strawberry poison frogs. Unlike the strawberry poison frogs we found, these frogs were much more difficult to catch. Males would sit out in the open on top of rocks and call. However, whenever we would get close, they would dive for cover. In many cases they would crawl into a deep crack or hole to the point where we would lose sight of them.
We found this species is two areas. The first, where we found a red form, was between a road and a stream in an area with secondary forest. The habitat was strewn with boulders and bromeliads were uncommon or absent. The second area was alongside a road but on a steep mountainside. Bromeliads were very abundant in the trees and we could hear the frogs calling from them. This was a higher elevation site than the first one and the form at this location was green, a pleasant surprise.

Oophaga granulifera 'red'

Photo copyright of: Brian Freiermuth

One of the target species for our foray to the pacific side of Costa Rica was the red granular poison frog, which we found calling, often on top of boulders, in secondary forest.

Oophaga granulifera 'green'

Photo copyright of: Brian Freiermuth

Green granular poison frogs were easy to hear from the bromeliads above us and below us. However, I was unable to capture any myself. Fortunately, our guide and operator of the Costa Rica Amphibian Research Center, Brian Kubicki was able to capture two males and a female for us to bring back to the Academy.

Bromeliads

Photo copyright of: Brian Freiermuth

Bromeliads were common in the roadside habitat where we found the green form of the granular poison frog.

The largest poison frog we found was the green and black poison frog, Dendrobates auratus. This species, like all members of the family, lays its eggs on land. When the tadpoles hatch they squirm onto the back of the adult who takes them to a water containing vessel. Green and black poison frogs were the only member of the family that we found on both coasts. We found them to be fairly abundant in most of the places where we found other species of poison frog.

Dendrobates auratus

Photo copyright of: Brian Freiermuth

Green and black Poison frogs were found frequently on both coasts of Costa Rica.

The final member of the family Dendrobatidae that we found was the Talamanca rocket frog, Allobates talamancae. The rocket frogs are generally drab in coloration compared to some of the more gaudy members of the family. These frogs aren’t generally kept by hobbyists but they perform many of the same parental care and reproductive behaviors as their more candy-colored relatives. The term rocket frog is definitely applicable to these frogs. The speed at which these frogs hop under cover made them very challenging to try to catch.

Allobates talamancae

Photo copyright of: Brian Freiermuth

This male rocket frog was photographed just after calling. Note the slightly inflated vocal sac.

Seeing these frogs in the wild was a very special experience for us. It allowed us to observe things that just can’t be described in books or blogs. The connection to nature is an intangible thing that has to be experienced to understand. Beyond that, seeing these animals in the wild allows us to understand them better in captivity. For example, the populations of strawberry poison frogs that we observed were heavily scewed towards females. We know from studies of this species in the wild that the females feed locations, not necessarily their own tadpoles. Could it be that having more females in a captive group could increase the success of the young because the tadpoles would not have to rely solely on one female to feed them? One thing that we are trying at the academy now is keeping larger groups of strawberry poison frogs together rather than splitting them into pairs as conventional wisdom would dictate. Time will tell if this experiment will bear fruit.


Filed under: Herpetiles — rainforest @ 7:41 pm

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