20 June, 1999
Charles Darwin Research Station
Howard L Snell

(Click frog for larger image)

The natural fauna of the Galapagos Islands contains four of the five classes of vertebrates. Various species of fish, reptiles, birds and mammals have been present in the Islands for the last several million years. One class, amphibians, has been unable to colonize the remote oceanic archipelago during all of that time primarily due its intolerance of salt water. Recent human activity and climatic fluctuations may have combined to alter the situation and frogs are now another introduced species within the Galapagos.

It appears that reproducing populations of frogs have become established on at least two of the five populated Galapagos Islands. A small (2 - 3 cm) arboreal frog of the Tree frog family Hylidae has been found increasingly frequently in Puerto Ayora, Isla Santa Cruz since 1998. The species, Scinax quinquefasciata, is a common frog of coastal lowlands in Ecuador. Seven individuals have been captured from three general areas within Puerto Ayora, the busiest port in the Galapagos. Additional observations and captures have occurred in Villamil on Isla Isabela, and observations of an apparently similar frog have been made in Puerto Baquerizo Moreno on Isla San Cristobal. One individual has been captured aboard a local boat, and another observed aboard a second vessel. Over the last 20 years individual frogs of at least two other species have been occasionally sighted within the ports of Galapagos, but breeding populations were apparently never established.

These populations represent the first known colonization by amphibians of the Galapagos Islands. Amphibians are generally conspicuously absent from the native faunas of oceanic archipelagos because their permeable skins place them in a negative water-balance with salt water. When in contact with the sea amphibians dry out as they lose fluids via osmosis to the more concentrated saltwater. Because of their inability to withstand even brief periods in salt water amphibians rarely survive long enough to reach oceanic islands by natural means such as rafting with floating mats of vegetation or floating across expanses of ocean. However, increasing human activity within the Galapagos archipelago requires large amounts of materials from continental Ecuador. Materials reach the islands as freight aboard one of five cargo ships making monthly calls to Galapagos ports or airfreight aboard one of the three jets arriving daily. Some of the frogs mentioned above where found within packages of vegetables from the continent and in standing water in stored automobile tires, others were found active upon the ground or in trees calling at night.

There is little published about the ecology of Scinax quinquefasciata, although a captive individual reportedly lived for nearly four years. Other species of the genus Scinax are resistant to desiccation and inhabit terrestrial environments where water is not always available. Breeding occurs in small temporary pools where females their eggs, which hatch quickly into tadpoles. The larval stage is relatively short and metamorphosis into froglets occurs quickly. Small pools of water and moist soil are common in gardens and around cisterns and leaking pipes within Puerto Ayora. Moist soil and pools of water are more common in the highlands of Santa Cruz, but there have been no frogs captured there yet. While no tadpoles have been discovered yet, the numbers, distribution, and sizes of adults within Puerto Ayora and Villamil suggests that breeding is occurring.

The first observations of this species within Galapagos occurred during 1998 at the height of the 1997-1998 El Nin~o event. Conditions were wetter during parts of those years than at any time since 1983. Severe flooding occurred throughout the coastal regions of Ecuador and reports of unusually dense populations of frogs were common. The current hypothesis of the dispersal of this frog to the Galapagos proposes that abundant populations in the continental port of Guayaquil allowed individuals to take refuge in materials bound for Galapagos by ship or plane. Once they arrived in the islands the unusually wet conditions allowed establishment which has persisted due to the increased availability of suitable microhabitats associated with human habitation.

It is impossible to predict the potential impacts of these frogs on the indigenous fauna of Galapagos. Frogs are mostly insectivorous so this species is presumably eating a variety of Galapagos insects and other invertebrates but we have no idea of the numbers nor species being consumed. Many frogs have poison glands within their skin, and introduced frogs have caused striking declines in the populations of naive native predators in other parts of the world. At this time we don't know if Scinax quinquefasciata possess such glands, nor if any Galapagos organisms are eating them. However, the general policy of the Galapagos National Park Service is to treat all alien species as potential threats to the natural biological diversity of Galapagos and to promote their eradication or control.

The current priorities concerning this newly introduced species aim to determine its distribution and rate of dispersal, compile information about potential means of eradication (any suggestions based upon experience are welcome - see contact information listed below), search for breeding sites, and perform some simple experiments to explore the potential toxicity to indigenous predators. All frogs found during these activities will be preserved, none will be left in the field. The Charles Darwin Research Station and Galapagos National Park Service are using this introduction in public awareness campaigns demonstrating the need for effective quarantine programs to protect the natural biological diversity of the islands.

We have produced a 450 k JPEG image of two specimens of these frogs. The image is available as an attachment to an automated response system. If you wish to receive the JPEG as an attachment please send a message to howard@fcdarwin.org.ec - Make sure that the subject line contains the phrase

send frog image

the body of the message should be empty (no one will read it).

We thank personnel of the Galapagos National Park Service and residents of Puerto Ayora and Villamil for collecting several of the frogs mentioned above. We also thank Drs. Robert Reynolds and Thomas H. Fritts of the U.S. Geological Service, and Dr. John Simons of the Natural History Museum of the University of Kansas for identifying the species from a specimen and photographs.

While a short account of this introduction has been published (Snell and Rea 1999), a more detailed account is in preparation. For more information please contact the following:

Aspects of this introduction:
Howard L. Snell (howard@fcdarwin.org.ec)
General Information about the Charles Darwin Research Station:
cdrs@fcdarwin.org.ec

Snell, H.L., and S. Rea. 1999. El Niño 1997 - 1998 en Galápagos: Se puede estimar 120 años de variaciones climáticas con estadisticas de 34?
In: P. Ospina and E. Munoz (eds.), Informe Galapagos 1998 - 1999, pp 65-71,
Fundación Natura, Quito, Ecuador.

This announcement was prepared by Howard L. Snell, Cruz Marquez and Marco Altamirano of the Vertebrate Ecology and Ecological Monitoring Department of the Charles Darwin Research Station. H. Snell and M. Altamirano are also of the Biology Department and Museum of Southwestern Biology of the University of New Mexico. The Charles Darwin Research Station is the operative branch of the Charles Darwin Foundation for the Galapagos Isles.