Camera trap, line transect census and track surveys: a comparative evaluation
Introduction
Efficient and reliable methods for rapid assessment of species richness and abundance are crucial to determine conservation priorities. Tracking animals by following footprints in dust, mud, sand or snow, is probably the oldest known method of identifying mammal's presence in an area (Bider, 1968). Counts of dung, nests, trails, calls and direct observation along line transects are also widely used for richness and abundance estimates (Eberhardt and Van Etten, 1956, Gannon and Foster, 1996, Fragoso, 1991, Fashing and Cords, 2000, Barnes, 2001, McNeilage et al., 2001). In the past years, new surveying techniques, using remote triggered photographic camera units, have become popular. The method is efficient for inventories, especially of cryptic animals, as well as for population studies of species for which individuals can be individually recognized by marks (Karanth, 1995, Carbone et al., 2001). Photo-trapping has also been widely used in population studies of tigers (Karanth and Nichols, 1998) and bears (Crooks et al., 1998; Kucera and Barrett, 1993, Mace et al., 1994). Capture–recapture models using photo-marked individuals have also been proposed for monitoring populations (Mace et al., 1994, Karanth and Nichols, 1998). Thus, camera-trapping furnishes an important non-invasive tool for assessing patterns of abundance throughout space and time, and their link with activity patterns, habitat use and reproductive information, which are key elements for wildlife conservation.
Despite the variety of field techniques that can be used for terrestrial mammal surveys, not all can be efficiently applied in every ecosystem and for all species. Some landscapes can be so remote, steep or so densely vegetated that only a few methods could be practicable. Sometimes the choice is limited not by technique efficiency, but by field costs. Track surveys are efficient and usually involve low costs, but depend on suitable field conditions and trained personnel (Burnham et al., 1980, Smallwood and Fitzhugh, 1995). Camera-trapping is more costly at the beginning, but is not so dependent on the environment to be sampled, constant assistance or even experienced field staff (Rappole et al., 1985).
There is an increasing need for comparing methods to be used in rapid faunal assessment, due to urgent conservation needs worldwide. In this paper, we evaluate camera-trapping, track survey and transect census efficiencies in detecting Cerrado fauna in Emas National Park, central Brazil.
Section snippets
Study area
This study was carried in Emas National Park (ENP) (18°19′ S, 52°45′ W), located in the central-western Brazilian plateau. The Park's 132,000 ha are composed mainly of grassland habitat (98%) covering a flat landscape. ENP is widely known for its rich and abundant grassland fauna (Redford, 1985) and is considered one of the country's best Cerrado Park (Erize, 1977).
Sampling
A total of 440 km of dirt roads is distributed across Emas Park. For this study we selected a segment of road in the north-central
Results
We accumulated a total of 24,840 h of camera-trapping, 30,600 h of track census and 28,050 h of faunal census (line transect) in the entire area. Of the 28 terrestrial medium–large sized mammal species found in the Cerrado grasslands of ENP, 19 (68%) were detected through track surveys, 17 (64%) through camera-trapping and 16 (57%) through direct observation. Track census was the most effective surveying method for detecting richness through time, reaching an asymptote after only 12 days (Fig. 1
Discussion
Track counts have proved to be the most efficient rapid method for detecting species richness and relative abundance in Emas Park, but some considerations should be taken into account. This method needs the minimum of two persons (a driver and an observer) and a vehicle, to cover extensive areas. The field personnel needs to have considerable experience with signs of the local fauna. Climate and ground conditions can be relevant limitations, and too wet or too dry ground can determine the
Acknowledgments
We thank Cyntia Kayo Kashivakura, Marcos Tortato, Thiago F. Rangel and all the volunteers that contributed with data collection and analysis. We also thank two anonymous reviewers for critical reading that greatly improved previous versions of the manuscript. We are also deeply indebted to Paulo Gustavo Prado, from Conservation International, for providing the necessary support to make this study possible. Work by J.A.F. Diniz-Filho was supported by CNPq. We are thankful to IBAMA for providing
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