Detectability of Caiman latirostris (Crocodylia: Alligatoridae) in Night Count Surveys

Abstract

Night count surveys are one of the most used methods to study distribution and population parameters in crocodilians. However, there are some methodological constraints that prevent the visualization of animals submerged or hidden behind vegetation. We studied the proportion of caimans that were detectable to observers during night count surveys based on the monitoring of seven adult Caiman latirostris females with radio transmitters (VHF, GPS, and UHF). Fieldwork was carried out in a protected area with a natural stream and a lagoon (30°11′26″S, 61°00′27″W) between 12 January and 29 April 2011 in Santa Fe, Argentina. Only locations acquired at night (18:00-05:00) were considered for analysis, and those acquired within vegetation were considered potentially undetectable. As the lagoon is mostly covered with vegetation (e.g., cattail), most of the animals were not visible to observers (62.5-100%, average > 80%). In contrast, virtually all individuals (100%) were potentially visible in the stream. The use of data collected in telemetry studies can be useful to estimate detectability of cryptic species such as the broad-snouted caiman. An understanding of animal detectability is necessary, as counts of individuals is often used in decision-making for crocodilian conservation, sustainable use, and control.