The dark side of the black caiman: Shedding light on species dietary ecology and movement in Agami Pond, French Guiana

Abstract

The black caiman is one of the largest neotropical top predators, which means that it could play a structuring role within swamp ecosystems. However, because of the difficulties inherent to studying black caimans, data are sorely lacking on many aspects of their general biology, natural history, and ecology, especially in French Guiana. We conducted a detailed study of the Agami Pond black caiman population using a multidisciplinary approach. The aim was to better understand the species’ dietary ecology and movements in the pond, and thus its functional role in pond system. We gathered natural history data, tracked caiman movements using satellite transmitters, and characterized feeding ecology via stable isotope analysis. Our study was carried out over three sampling periods and spanned both wet and dry seasons, which differ in their hydrological and ecological conditions. Our results show that black caiman abundance and age demographics differed between seasons in Agami Pond. In the dry season, Agami Pond is one of the only areas within the marsh to hold water. It thus contains large quantities of different fish species, which form the basis of the black caiman’s diet. Caiman body size, a proxy for age class, was around 1.5 meters. During the wet season, which corresponds to the breeding period for migratory birds (e.g., Agami herons), adult black caimans are present in Agami Pond. Adults were most abundant in the inundated forest. There, most individuals measured up to 2 meters. They also exhibited a particular “predatory” behavior near bird nests, preying on fallen chicks and adults. Juveniles and subadults were present during both seasons in the pond’s open waters. These behavioral observations were backed up by stable isotope analysis, which revealed ontogenetic variation in the caiman’s isotopic values. This isotopic variation reflected variation in diet that likely reduced intraspecific competition between adults and young. The telemetry and microchip data show that different age classes had different movement patterns and that seasonal variation in the pond may influence caiman prey availability and reproductive behavior. The new information gathered should help predict this species’ responses to potential ecosystem disturbance (e.g., water pollution, habitat destruction) and inform the development of an effective conservation plan that involves locals and wildlife officials.

Relationships between stable isotopes and trace element concentrations in the crocodilian community of French Guiana

“…Except for M. niger stable isotopes, which were analysed as described in Caut et al (2019), all nitrogen and carbon stable isotopes were determined in freeze-dried whole blood (aliquots mass: ~0.3mg) with a continuous flow mass spectrometer (Thermo Scientific Delta V Advantage) coupled to an elemental analyser (Thermo Scientific Flash EA1112). Results are presented in the usual 𝛿 notation relative to the deviation from standards (Pee Dee Belemnite for 𝛿 13 C and atmospheric nitrogen for 𝛿 15 N), in parts per thousand (‰) following the formula…”

Home range and habitat use of two sympatric crocodylians (Melanosuchus niger and Caiman yacare) under changing habitat conditions

“…Campos (2002) radio tracked 18 individuals of C. yacare for seven months and found that HR varied from 3 to 248 ha, well above our mean HR for C. yacare (0.47 ha). Caut et al (2019) reported an average HR of 1.21 ha for M. niger in French Guiana studying four individuals for one year. This same study reports that M. niger HR averaged <1 ha in most months, except in December, when it reached 13.31 ha.…”

Landscape features affect caiman body condition in the middle Araguaia River floodplain

“…Therefore, we created circular buffer areas with 500‐m, 1‐km and 3‐km radii centered at each capture point to calculate landscape metrics for characterization, assessment and measurement of human‐modified landscapes. Based on home range studies that estimated caiman home ranges between 0.048 and 3.5 km 2 , we considered buffer zones as a utilization area of caimans (Ouboter & Nanhoe, 1988; Campos et al ., 2006; Caut et al ., 2019; Marques et al ., 2020b).…”