Occurrence of Caiman latirostris and Caiman yacare in the Middle Delta of the Paraná River, Argentina

Abstract

There are two species of caiman in Argentina. The yacare caiman Caiman yacare, which is found in the provinces of Chaco, Corrientes, Formosa, Misiones, Salta and Entre Ríos, and the broad-snouted caiman Caiman latirostris that inhabits Chaco, Corrientes, Entre Ríos, Formosa, Jujuy, Misiones, Salta, Santa Fe and Santiago del Estero (Prado et al., 2012). Both species are listed as of Least Concern in the IUCN Red List (Siroski et al., 2020; Campos et al., 2020). There have been anecdotal reports of both species in various localities of the Middle Delta of the Paraná River in the north of Buenos Aires (Chebez, 2008). Caiman occasionally use rivers for dispersal, thus reaching more southern latitudes than is usual for them, these are generally adult individuals, often males that move south in the summer, but it is unknown if they manage to survive the winter (Restivo et al., 2011). It has been proposed that between 30° and 34° south latitude, the thermal conditions may be incompatible for the feeding and digestion of C. latirostris for about 5 months of the year (Diefenbach, 1988). This is because, during winter and into early spring, the air temperatures and limited sunlight (due to short daylight hours, and a high frequency of cold and overcast days) do not allow the animals to reach their preferred body temperature. Furthermore, a critical limitation for the survival of C. latirostris eggs is the strong seasonality, with minimum temperatures dropping below 0 °C in winter (Simoncini et al., 2009; Viotto et al., 2022). The objective of the current study was 1) to record caiman occurrences in the Middle Delta of the Paraná River during the extraordinary low water of the Paraná River that occurred between 2020 and 2022, and 2) confirm the winter survival of caiman in this area.