Amphibians of Laguna del Tigre National Park
Laguna del Tigre National Park is a challenging environment for amphibians. For a tropical forest it receives relatively little annual rainfall and most of that falls within just a few months each year. Due to high temperatures and porous bedrock, after about three days without rain the forest dries considerably. For a few months each year, from January to March, the forest is at its driest. Many species of trees lose their leaves to save water and all but the deepest lagoons dry up. So this limits the activity of most water loving amphibians.
When the rainy season starts however, amphibian activity can go through the roof. It is quite amazing to see just how many individuals suddenly appear to make use of the favourable conditions and breed. It always makes me wonder where they all go during the dry season.
There are 24 species of amphibians recorded in Laguna del Tigre, and many of them are regular favourites like Mexican treefrogs (Smilisca baudinii), leopard frogs (Rana brownorum), sheep frogs (Hypopachus variolosus), and of course red-eyed treefrogs (Agalychnis callidryas).
However, every now and then a real treat turns up. And this year (2017) we got REALLY lucky! Two species of frogs that are infrequently seen turned up. Both species are specialists of drier environments, and spend most of the year hiding away, waiting for the rains to bring them out.
After several years of abnormal weather, drought, followed by El Niño and La Niña, we finally had a “normal” rainy season that started roughly on time in June. That brought amphibians out in their masses. Huge choruses of treefrogs were seen around Las Guacamayas and on the trails in the lower forests. Multiple choruses calling all at the same time made a cacophony so loud it difficult for us to hear other members of the Indigo field team.
Most of the commonly seen species came from the treetops. Small-headed treefrogs (Dendropsophus microcephalus), mahogany treefrogs (Tlalocohyla loquax), Mexican treefrogs (S. baudinii), Staufer’s treefrog (Scinax stauferri), and red-eyed treefrogs (A. callidryas) were seen in great numbers and at pretty much every suitable water body for two months.
But for a short while on a small section of trail in the low forest we were lucky enough to see a very strange frog indeed. The first one we saw was on a small branch high up in a tree. With the naked eye it looked different from anything else we had been seeing, but it was difficult to tell.
A photograph with a telephoto lens helped confirm it was a casque-headed treefrog (Triprion petasatus).
Casque-head’s, as they are affectionately known, are considered to be a common inhabitant of the wider Yucatán Peninsular. However, they are not commonly seen due to their habit of spending most of the year tucked up in tree hollows waiting for the rains and the onset of the breeding season.
It was not long before we were finding more of them. We had not seen this species since the very first expedition we ran way back in 2013, so to finally find them again was particularly exciting.
Another unusual amphibian we encountered is even harder to find. As well as there being lots of treefrog activity, terrestrial frogs and toads were also out in force. Tungára frogs (Engystomops pustulosus), fringe-toed frogs (Leptodactylus melanonotus), white-lipped frogs (Leptodactylus fragilis), and Gulf Coast toads (Incilius valliceps) frequently added their voices to the choruses of the treefrogs.
While taking the 7km walk to the Mayan ruins of Wak’a we experienced the results of a successful breeding season. The path was covered with newly metamorphed toads (Incilius valliceps). We really had to watch our step in order to not tread on the tiny toads. After about 20 minutes of assault course like walking I noticed something different about the way one of these toads was moving. It didn’t have the same gait as the rest. By tiny, I mean no bigger than my little finger nail. I crouched down to get a closer look. I quickly confirmed that not only was the little amphibian moving differently, it looked very different too. It was a baby Mexican burrowing toad (Rhinophrynus dorsalis), a very strange looking amphibian indeed.
Mexican burrowing toads spending most of the year underground feeding on ants. They only come the surface to breed for a few hours each year. The males call by inflating the large globulous bodies and floating on the water’s surface. The noise the make can best be described as a loud ‘whooooooaaaaa’ that sounds something like a UFO landing.
Soon after the first one had been spotted we realised that this section of path was covered in tiny Mexican burrowing toads. It was a very exciting moment, it was only the third time I have seen them in Laguna del Tigre!
In total, over two months this summer we saw 16 species of amphibians, approximately 66% of all species currently known from the park. Quite amazing, especially with the appearance of two rarely seen species.