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THE INFLUENCE OF WEATHER ON OBSERVATIONS OF PALEOSUCHUS TRIGONATUS (SMOOTH-FRONTED CAIMAN)

Hallie Cowan

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Paleosuchus trigonatus is a species of small caiman that inhabits small streams in the canopy-covered jungles of northern South America. There has been little research done on this habitat specialist including their behavior and how they adapt to their unique environment. Using data collected by the Secret Forest Research Station on the Tambopata River in the Peruvian Amazon we looked at how cloud coverage, rainfall patterns and temperature affect their activity. This study analyzed 15 reports of P. trigonatus between April 2020 and May 2022 made by the Secret Forest herpetology team. We found most of the caimans were detected on nights with relatively clear skies, little to no rain during the day and an air temperature of 26 degrees celsius. This data on their preferred weather conditions is important as the climate in the region changes. Data from the study could suggest how this habitat specialist could be affected as the frequency of their preferred weather conditions change.

Blue pin represents Secret Forest research station where data was collected. The blue line represents roughly where the surveyed stream is located.

ABSTRACT

BACKGROUND

  • We hypothesize that variables like temperature and cloud cover affect P. trigonatus less than other crocodilians because, unlike other crocodilian species, they don’t need to bask. They have lower body temperatures and nesting temperatures because of their preferred habitat, which are streams in the canopy covered rainforest (Magnusson et al., 1985). This also makes them harder study subjects, making there limited information on them.
  • Although they are of least concern on the IUCN Red List, their habitat in the Amazon is at risk of heavy human disturbances and climate change.
  • Data was collected between April 2020 and May 2022 at the Secret Forest Research Station situated along the Tambopata River in the Madre de Dios Region of Peru.Larger caimans were caught with snare poles, hatchlings, juniniles, and small sub-adults were hand grabbed. These captures were authorized under SERNAMP.
  • Most data was collected during transect surveys along a 1 kilometer long section of stream, though some data reported is from occasional opportunistic sampling events.
  • Biometrics were taken at the capture site including snout-vent length, weight, and total body length. They were PIT tagsged and released right away. Environmental conditions were also recorded that night including temperature, rainfall that day and cloud cover. Rain was recorded on a scale from 0-5 based on how much rainfall there was during the day. Cloud cover was also recorded on a scale from 0-5.

REFERENCES

Magnusson, W. E., & Lima, A. P. (1991). The Ecology of a Cryptic Predator, Paleosuchus tigonatus, in a Tropical Rainforest. Journal of Herpetology, 25(1), 41. https://doi.org/10.2307/1564793

Magnusson, W. E., Lima, A. P., & Sampaio, R. M. (1985). Sources of Heat for Nests of Paleosuchus trigonatus and a Review of Crocodilian Nest Temperatures. Journal of Herpetology, 19(2), 199. https://doi.org/10.2307/1564173

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CONCLUSION

  • The preferred temperature for activity with P. trigonatus is 26 degrees celsius and on nights with no rain
  • 6 out of the 15 captures were recaptures. This demonstrates individuals remain in the same area, potentially because of the territoriality of males (Magnusson et al.,1991).
  • Future work would seek to confirm these initial findings. Captures at different times of the year would also be valuable to see if this behavior is consist or variable according to potential climatic changes.

Nine individual caiman were captured with 6 recaptures. Most of the caimans were found on nights with relatively clear skies and little to no rain during the day. The most sightings occurred when it was 26 degrees celsius. Caimans were also always found either in the water or on the banks, never more than one body length away from the streams or water source.

RESULTS

METHODS

ACKNOWLEDGEMENTS

Photo by Nicholas Hess.

I would like to thank Dr. Ray Ball for helping and supporting me in every step. I would also like to thank Reed Ebbinghaus and Chris Ketola from Fauna Forever for collecting data and working to support the project.