Tracking Trinidad's Treefrogs

Leaf nesting frog (Phyllomedusa trinitatis) from Trinidad. Photo by Renoir Auguste

One of the fundamental aspects of assessing the ecology of an animal, is to track its movement. Often, this is difficult as animals cannot be observed continuously. One way to off set this disadvantage, is with the use of tracking devices. However, tracking methods can have both advantages and disadvantages.

The leaf nesting frog (Phyllomedusa trinitatis) is a frog found in Trinidad and Venezuela (Murphy et al. 2018). An evaluation study on tracking the movement of this species was undertaken at Simla, in the Arima Valley in Trinidad (Gourevitch and Downie 2018). Tracking devices consisted of (1) harness made of cotton with bobbins, and (2) radio-tags. Observations on the frogs were conducted in lab and in the field.

Twenty-six frogs were assessed, with 16 of these successfully tracked. Both methods presented challenges. However, the locations of where the 16 frogs (1 female and 15 males) rest during the day were revealed and gives greater insight to the habitat use of these frogs. Further, the female that was tracked appeared to move further away from the breeding pool than the males. Though both tracking methods appear to not work perfectly for Phyllomedusa trinitatis, the study emphasizes the need to test out tracking methods on different species in their respective habitats.


Citations:

Gourevitch, E.H.Z., and Downie, .J.R. 2018. An evaluation of of tree frog tracking methods using Phyllomedusa trinitatis (Anura: Phyllomedusidae). Phyllomedusa: Journal of Herpetology 17: 233-246.

Murphy, J.C., Downie, J.R., Smith, J.M., Livingstone, S.R., Mohammed, R.S., Auguste, R.J., Lehtinen, R.M., Eyre, M., Sewlal, J.N., Noriega, N., Casper, G.S., Anton, T., Thomas, R.A., Rutherford, M.G., Braswell, A.L., and Jowers, M.J. 2018. A field guide to the amphibians and reptiles of Trinidad and Tobago.  Trinidad and Tobago Field Naturalists’ Club. 336 pp.

The elusive and important freshwater turtles of Trinidad

One of three native freshwater turtles on Trinidad: Gibba turtle (Mesoclemmys gibba) Photo by Renoir Auguste.

Trinidad and Tobago are well known for the nesting marine turtles along the coasts. There have been numerous conservation efforts to highlight their importance thanks to local community groups, and international bodies. Typically, when a local person thinks of 'turtle' the Leatherback (Dermochelys coriacea) might usually come to mind more often than any other. However, Trinidad has three native freshwater species of turtles. Surprisingly, not many people are aware of these three turtles’ existence on Trinidad. 

The first of the three native species is perhaps currently the most commonly encountered: The Galap or painted wood turtle (Rhinoclemmys punctularia) from the family Geomyididae. This family is the most species rich family of turtles globally with about 75 species recorded. They are represented with species across Europe, Asia, Africa and Central and South America. The Galap is the sole species from the family here. Individuals grow to an average size of about 20 cm. They can be identified by having red blotches on the crown of their head, yellow reticulations near the ear, and yellow or red spotted scales on the forelimbs. The Galap appears to be mainly found in south Trinidad with populations north centrally as well. Their habitat mainly consists of ponds or streams in forests, and can also be found at road side ditches. They are omnivores, and are known to act as seed disperses as they feed on fruits thus contributing to plant growth which benefits plants, other animals, and humans. 

Galap (Rhinoclemmys punctularia) feeding on fruit in south Trinidad. Photo by Renoir Auguste

The second of the three native freshwater turtles is the scorpion mud turtle (Kinosternon scorpioides) from the family Kinosternidae. This family has 25 species and are restricted to the western hemisphere. The scorpion mud turtle is the sole species on Trinidad currently, although subfossil remains hints at another species once being here. They grow to about 27 cm. The turtle can be identified by their domed carapace (shell) which varies from light brown to olive, with a brown-yellow head. They appear to be distributed across the south and northern basins of Trinidad; similar to the Galap. They may be found in temporary or permanent freshwater habitats, roadside ditches, and stream impoundments surrounded by forests. Although it may be relatively common, they are not always commonly seen and this may be because they bury themselves in the bottom of the pond or stream where they reside when it dries up, or are almost always under water when wet. Like the other two species they are nocturnal but may be active during the day. They are predominantly carnivores feeding on insects, molluscs, crustaceans, fish, frogs, worms, and mammals, but will consume algae and plant matter, including fruits thus also making them potential seed disperses.

Scorpion mud turtle (Kinosternon scorpioides) from central Trinidad. Photo by Rainer Deo

The third native freshwater turtle species is perhaps the rarest on the island and rarely encountered: the Gibba turtle or side neck turtle (Mesoclemmys gibba) from the family Chelidae. There are about 53 species restricted to Central and South America. They are able to move their necks sideways into the shell (hence the common name). All are highly aquatic with the capacity to stay submerged for long periods of time. The Gibba turtle grows to about 30 cm. They can be identified by having a wide and flattened head with two barbles on the chin, dark brown or black carapace or shell and extensive webbing in the feet. Very little is known about this species locally. Previous literature suggests it is an uncommon lowland species. A survey published in 2010 found that they were restricted to the South Oropouche catchment based on anecdotal evidence from locals. However, as of 2018, individuals have been spotted by myself not far from the Aripo Savannas Scientific Reserve which is designated an Environmentally Sensitive Area in Trinidad. Like the other two species, they prefer areas with stagnant waters in forests, however with closed canopy. This suggests they would be susceptible and sensitive to habitat alteration. They are also nocturnal and are omnivores: also feeding on fruits like the other two species.

Gibba turtle (Mesoclemmys gibba) from northern Trinidad. Photo by Renoir Auguste

Given the high precedent to marine turtle conservation, these three freshwater turtles should also be considered for priority conservation in Trinidad. They are an important component of the local fauna and ecosystems because of their seed dispersing capabilities and varied diet. They also comprise an important component of freshwater ecosystems. Greater effort towards learning more about their ecology is needed, which would not only benefit the local population of turtles but the freshwater ecosystems where they reside, other wildlife, and people.

Murphy, J.C., Downie, J.R., Smith, J.M., Livingstone, S.R., Mohammed, R.S., Auguste, R.J., Lehtinen, R.M., Eyre, M., Sewlal, J.N., Noriega, N., Casper, G.S., Anton, T., Thomas, R.A., Rutherford, M.G., Braswell, A.L., and Jowers, M.J. 2018. A field guide to the amphibians and reptiles of Trinidad and Tobago.  Trinidad and Tobago Field Naturalists’ Club. 336 pp.

The frog Leptodactylus nesiotus is no longer endemic to Trinidad

Leptodactylus nesiotus from Trinidad. Photo by Renoir Auguste.

As of 2014, the island of Trinidad was known to have four species of endemic frogs: Trinidad stream frog Mannophryne trinitatis, Urich's litter frog Pristimantis urichi, Golden tree frog Phytotriades auratus and Trinidad thin-toed frog Leptodactylus nesiotus. 

In 2015, there were now three endemic species after the discovery of the Golden tree frog (Phytotriades auratus) in Venezuela (Rivas and de Freitas 2015). Now, at the end of 2018, the number of endemic frog species is down to two after Leptodactylus nesiotus were discovered in the Guianas (Guyana, Suriname and French Guiana), South America.

The Trinidad thin-toed frog (Leptodactylus nesiotus) is a member of the Leptodactylus melanotus group. They are known from swampy areas in south west Trinidad and also from the Nariva Swamp. Jairam and Fouquet (2018) reported on specimens occurring along coastal savannas and swamps on mainland South America, along the Guianas. Given the very wide distribution and continuity of habitat, the authors suggest that specimens of L. nesiotus may have been mistaken for L. validus or other species of the L. melanotus group. They also suggest that specimens are also likely to occur in Venezuela and may even occur in Colombia and Brazil. 

Little is known about the biology of the species from Trinidad and prior to its discovery in South America, it was given the IUCN Red List Status of Vulnerable. With an extension of greater than 1000 km, perhaps the status of Vulnerable now needs to be reassessed to Least Concern. 

It is unsurprising that L. nesiotus is not an island endemic to Trinidad, especially given its main population in south western Trinidad is less than 20 km from Venezuela. Also, in Trinidad, the species has been observed to live alongside L. validus. Perhaps further investigations of other endemics may reveal a much wider distribution, which further highlights the biogeographical link to the Trinidad and South America fauna.

Literature Cited

Rivas, G. and de Freitas,M. 2015. Discovery of the critically endangered Golden tree frog Phytotriades auratus (Boulenger, 1917), in eastern Venezuela, with comments on its distribution, conservation, and biogeography. Herpetological Review 46: 153-157.

Jairam, R. and Fouquet, A. 2018. First records of Leptodactylus nesiotus (Anura: Leptodactylidae) for Guyana, Suriname and French Guiana. Herpetology Notes 11: 997-999.