Dr. Enrique La Marca is a professor at the University of the Andes in Mérida, Venezuela. This is the latest report from field researchers participating in CI’s Search for the Lost Frogs campaign. Read our previous blog posts here.
It has been 28 years since my team discovered the elusive scarlet frog (Atelopus sorianoi) in the Venezuelan Andes; eight years later, it was gone. It is difficult to overcome the discouragement of not seeing this wonder of the tropical montane humid forests anymore.
In the course of those early times, the frogs were seen year after year at a single locality. In one opportunity, a massive reproductive explosion took place, and cars smashed dozens of adult frogs while they were trying to cross a road cutting through their habitat. Like some toads in the same family as our harlequin frog, adult scarlet frogs congregated during the rainy season to reproduce. Hundreds of these amphibians moved to streams to find mates and to lay strains of eggs attached to rocks and fallen tree branches and trunks.
1990 was the year when the last large group of frogs showed up. Specimens collected in 1998 carried a pathogen fungus that has proved to be lethal to amphibians. Perhaps this was the ultimate cause for the population crash.
In the search for this lost frog, our exploring team detected other factors that also could account for the decline and possible extinction of the population where it was originally found. In spite of being the middle of the rainy season, skies were cloudless even at times of the day when in the past there was heavy fog or clouds. We saw that massive land transformation had taken place nearby, with forests cleared for agriculture or cattle fields. Forest clearance may account for the lack of cloud formation, directly affecting the microclimatic conditions that prevailed for centuries. With less cloud cover, the solar radiation gets stronger, raising temperatures and diminishing the amount of humidity in the environment, thus creating adverse conditions for frogs.
Nowadays, extreme precipitation events seem to occur at a higher rate than in past decades. Frog populations may be washed out during those events, causing reproductive failure. We saw several landslides in a road heading to and close to the survey site, and a huge landslide erased the entrance to the trail leading into the site, making our survey there an experience that required mountain climbing equipment and techniques.
We have not discarded the possibility that the scarlet frog still may survive in some of the forest remnants nearby. There are some cloud forests within a national park that seem to be in pristine condition. If the loss of humidity and the presence of the lethal pathogen have not affected those potential populations, there is still hope that we can find the scarlet frog. Indeed, locals told us of the presence of some orange frogs they saw a couple of years ago in a nearby forest. We are heading there next.