Microhylids or Narrow-mouthed toads are represented by three species in Costa Rica.

They are probably best known by their loud buzzing vocalizations, to me reminiscent of a motor running at a high RPM, or a propeller plane moving by. Following periods of heavy rains microhylids will come to ponds and puddles to breed, to lay eggs.

Frogs as a group try to avoid ponds with fish. These are creatures which will eat the eggs young. While bodies of water will offer some advantage to eggs and tadpoles, they do not ensure safety to the adults which congregate at them and advertise their presence.

(Gastrophryne pictiventris) calls from the water surface, the frog to the left is holding on to a pond side leaf, while calling outward. Perhaps as a defensive measure, the calls of one male, run into and overlap others. Making it difficult to pinpoint the individual vocalist.


Costa Rica and Biogeography
A definition of biogeography as the word indicates, is the study of life, (organisms, and species), relative to where it is found now, and over time.

The number of species found in an area, ecosystem or region, is known as biodiversity. And to understand why Costa Rica has such a high biodiversity–that is so many species within the borders of a republic which is roughly the size of Denmark or West Virginia, requires an understanding of this country’s location, history, climate now, and in the past. Obvious geographic facts point to Costa Rica’s perch on the Isthmus of Central America, between the continents of South America and North America. It is also located between two oceans–the Pacific to the west, and the Atlantic Ocean and Caribbean Sea to the east.

I’ve stood on a high mountain peak in alpine tundra or paramo along continental divide on a clear day, my finger tips were cold, and there was frost at my feet, and looked out over the Caribbean and Atlantic ocean on one side, and then turned to see the peaceful Pacific Ocean on the other. From such a vantage point with the crisp morning air cool enough to see my breath, I could look out across mountains, and foothills, to the lowlands, and hot humid rainforests on both sides.

From such a vista, very little of the amphibian world is truly visible. These peaks, mountains, foothills and lowlands, with their different soils, and differing rainfall amounts, all harbor plant communities adapted to the changing conditions and microclimates. The result is a very high number of plant species, compressed across just a few miles.This high species diversity in plants in turn provides habitat and niches for a high species diversity of insects, of animals, and all that comes with these tropical forest zones, or ecosystems.

Costa Rica (map adapted from Google Earth)
Costa Rica is shown with the Caribbean Sea and Atlantic Ocean to the East and the Pacific Ocean to the west. To the north, beyond Central America and Mexico, is the rest of North America. To the south, beyond the Isthmus of Panama, you find South America.

The tropics are defined as those the latitudes occurring between the Tropic of Cancer south past the Equator to the Tropic of Capricorn. Costa Rica is situated north of the Equator and south of the Tropic of Cancer roughly between 8° and 11° North in latitude. This part of the globe gets more direct sunlight, greater energy from the sun (or solar insolation) than areas further from the equator. This in short makes places like Costa Rica, warm. Moving up in elevation however, is a lot like moving further from the Equator. That is, the higher up a mountain you climb, the cooler it gets. Here, there is less air to trap heat radiated from the earth’s surface. Think of there being less of a blanket of air or atmosphere at higer elevations. Ironically their is less air and atmosphere to protect you from the suns rays..

Costa Rica with four mountain ranges, and peaks rising over 10,000 feet, or 3100 meters, then contains areas of warm, as well as areas or ecosystems of cooler more temperate climate. Costa Rica with its great elevational range over comparatively short distances, as well as regions with distinctly different amounts and patterns of rainfall. These same mountain ranges, and their effects upon prevailing winds, also affect the climate, the temperature and the amount of rainfall. To the northwest it is warm, and for part of the year dry, or less humid. Here we have dry forest and humid forest in the lowlands and foothills of the Pacific Slope. Further south along the Pacific Slope of Costa Rica moving towards Panama, it becomes more humid, with impressive rainforests again surrounding Golfo Dulce, and the Osa Peninsula. Where the tradewinds move up this Pacific Slope, as they rise, the air cools, and mist, fog and light rain occurs forming pre-montane wet forest, or more famously named “cloud forest”.

Differences in climate, results in areas with different plants, forests, and forest creatures. Costa Rica also owes elements of it’s biodiversity to species originating in South America, as well as North America. Long periods of stability in climate, provides an environment in which creatures can fine tune their niches, they can specialize to a particular forest and resource over the thousands of years that it remains stable. This may result in greater specialization, and accordingly speciation, the formation of distinct types of animals, of new species. Mountain ranges may also act as islands in biogeographical terms. Areas cut off or isolated from other populations of the original form on an organism or group. Again, over the millennia, these isolated populations may change slightly, diversify, and specialize to the point of forming new species over time. And so this is in part how biogeography plays a role, in how many species are in a place, and why.

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