Studying black caimans in and out of their pond
Crocodilians are tropical wetland ecosystems’ top predators, but they are rarely studied. Black caimans, which live between Central America and the northern part of South America, saw their population drop by 90 % in the 20th century. To have a better understanding of their behavior, scientists used Argos PTTs to track them in a nature reserve in French Guiana.
Wetland top predator
The black caiman (Melanosuchus niger) is a predator living in wetlands areas of the tropical regions of the Americas. They prey on fish, birds, mammals, etc. During the 20th century, they were heavily hunted, in particular for their hide. They are now fully protected In French Guiana, but not fully understood. Black caimans are easily disturbed animals, difficult to observe in the wild, since they spend long periods of time submerged and/or out of sight. All those traits make remote monitoring tools especially useful to study them, even if using satellite telemetry is not easy on crocodilians.
In the middle of a series of large mangrove swamps lying between the Amazon River estuary in Brazil and the Cayenne Peninsula in French Guiana, Kaw-Roura Marshes, a biodiversity hot spot natural reserve, are the most distant from the Amazon River estuary. A few permanent areas of open water (ponds) are fond there among water bodies covered by floating vegetation. Among those ponds, the Agami pond holds a population of black caiman. It undergoes seasonal variations — in the dry season, it is one of the only areas within the marsh to hold water. A floating scientific platform was built in 2001 to study this unique and largely uncharacterized ecosystem.
A multidisciplinary study
A multidisciplinary black caiman study was conducted there, including survey of the caimans with DNA and stable isotopes analysis, direct observation and Argos satellite telemetry. The aim was to better understand the species’ dietary ecology and movements in this particular pond, and thus its role in pond ecosystems in general.
Four black caimans were tagged with Argos PTTs, one female and three males. Their behaviors were different depending on the sex, and also on the seasons and the food availability. The fact that the Agami pond is a major nesting site for a number of water birds seems to entice the caiman to stay there till June. The three tracked males then left, possibly for breeding, going in different directions up to about 4 km away, while the female stayed (possibly not breeding that year). The two males still tracked the following year went back at the time the Agami herons also returned.
It is important to understand black caiman home range dynamics to develop and implement feasible conservation plans for such top predators. Findings on the trophic ecology and movement patterns of Agami Pond black caimans are a first step towards the better conservation of this species in French Guiana. However, further research is needed, since we still know very little about their movements, breeding and nesting sites.
Caut S, Francois V, Bacques M, Guiral D, Lemaire J, Lepoint G, et al. (2019) The dark side of the black caiman: Shedding light on species dietary ecology and movement in Agami Pond, French Guiana. PLoS ONE 14(6): e0217239. https://doi.org/10.1371/journal.pone.0217239
Male black caiman with an Argos satellite transmitter attached to its head (photo S Caut)