Are playback-aided surveys of the buffy-tufted-ear marmoset (Callithrix aurita) improved with the use of handheld thermal cameras?

Obtaining accurate data on occurrence, abundance, and population density of endangered species is of paramount importance. Accordingly, we need a continuous effort to improve current survey methodologies. One such possibility is the use of handheld thermal cameras to assist in playback-aided surveys. Here, we tested this possibility with our model species, Callithrix aurita, a small, endangered primate that inhabits the Atlantic Rainforest of southeastern Brazil. We hypothesized that the thermal camera would allow: (1) the identification of non-responsive groups or lone individuals; and (2) the detection of more individuals in cases where the groups approach the playback location. We surveyed four Atlantic rainforest fragments using the playback-aided active search methodology, complemented with scanning the surroundings with a handheld thermal camera. We did not identify any unresponsive groups/individuals, and were able to identify 51 individuals with the naked eye and 43 using the thermal camera, a non-significant difference, rejecting both hypotheses. We believe this result was due to the survey being carried out by a researcher highly trained on the study species. Therefore, on these grounds alone, our study does not support the use of thermal cameras in similar situations. However, on two occasions, we obtained more sightings of primates through the camera. Thus, the use of the device may result in an improvement in the quality of playback-aided surveys of Callithrix aurita populations, for which accurate data is crucial. We discuss the limitations and possibilities of use of thermal cameras with other primate species (e.g. fearful, living in large groups, nocturnal, unresponsive to playbacks, small-sized, cryptic or elusive, or that use hollows), and point directions where future research is needed.