Detectability of Caiman latirostris (Crocodylia, Alligatoridae) during night count surveys in Argentina

PORTELINHA, T.C.; VERDADE, L.M.; PIÑA, C.I.

Manila

Congreso; 21st Working Meeting of the Crocodile Specialist Group; 2012

Crocodile Specialist Group

Night count surveys are one of the most used methods to study distribution and determine some populations? parameters in crocodilians. However, there are some difficulties and biases during the sampling preventing the visualization of animals submerged or hidden among vegetation. We investigated the proportion of caiman available to be observed during a night count survey based on the positions of eight adult females of Caiman latirostris in which we have installed radio transmitters (VHF, GPS and UHF). Field work was carried out in a protected area with a natural stream and lagoon (30º11?26?S 61º0?27?W) between January/2011 and March/2011. We only considered for analysis locations acquired during night (between 18:00h and 05:00h) and those acquired inside vegetation were considered undetectable. Lagoons with greater availability of vegetation (cattail) can offer refuges and therefore more than 80% (100-60%) of the animals were hidden and not able to be visualized during surveys, on the other hand in the stream 100% of the caiman were located in an area where they could be observed. We did not observe a relationship between female body size and the possibility to be visualized. The best hours to do a survey seem to be between 22:00h and 03:00h.