Giant Anteater (Myrmecophaga Tridactyla) Population Survey in Emas National Park, Brazil-A Proposed Monitoring Program

Article excerpt

Abstract

The population density of giant anteaters (Myrmecophaga tridactyla) at Emas National Park in central Brazil was estimated to determine the most suitable method to monitor this population. The data obtained is expected to underpin a more thorough evaluation of the population's recovery rate following a fire in 1994, and factors possibly affecting its numbers significantly. Population estimates were based on: 1) linear terrestrial transect surveys (distance method), which led to a density estimate of 0.396 [+ or -] 0.069 (se) individuals/[km.sup.2] for the park's flat area; 2) aerial surveys with double count correction, showing an estimated 0.209 [+ or -] 0.104 and 0.196 + 0.065 (se) individuals/[km.sup.2] for the Park's central and flat areas, respectively. A preliminary giant anteater population-monitoring proposal was outlined based on aerial count data. A power analysis indicated that, to achieve a > 90% probability of detecting a 5% annual population decline, a monitoring program would have to be established using five transects repeated five times a year for 18 years, four times a year for 17 years, or three times a year for 21 years. Terrestrial transect surveys seem more appropriate for more accurate estimates, although aerial surveys may be the best option in most cases.

Introduction

The giant anteater (Myrmecophaga tridactyla L. 1758) is the largest extant representative of the order Xenarthra, with adults weighing 20 to 40 kg (Emmons 1990; Nowak 1999; Eisenberg and Redford 1999). Currently, large known populations of giant anteaters in Brazil are restricted to a few sites, e.g., Serra da Canastra National Park (SCNP) in Minas Gerais state (Shaw, Carter and Machado-Neto, 1985), Emas National Park (ENP) in Goias state, and the Pantanal wetland areas (Medri and Mourao, 2005). This species is considered at risk for extinction (vulnerable) in Brazil (MMA 2003) by the International Union for the Conservation of Nature and Natural Resources (IUCN), and is listed in CITES Appendix II (IUCN 2004).

Estimates of giant anteater population size or density are scarce, and available data precludes direct comparisons since they were obtained by different methods (Shaw et al. 1985, 1987; Coutinho et al. 1997). However, population surveys are the basis of population monitoring, which is essential for underpinning management strategies (Sutherland 2002a; Greenwood 2002). Mourao et al. (2000) suggested the use of standardized monitoring plans based on aerial surveys for some vertebrate species of the Pantanal region. Similarly, Tomas et al. (2001) emphasized the need for terrestrial surveys to monitor pampas deer populations in the same area. Information on monitoring methods for giant anteater populations is virtually nonexistent.

Habitat deterioration and reduction are the main causes for the decline in populations (Fonseca et al. 1999), although brush and forest fires may significantly impact this species (Silveira et al. 1999). In August 1994, 97% of ENP was destroyed by fire, including all of its grasslands. Silveira et al. (1999) estimated the death rate of large mammals, particularly giant anteaters, using the distance method and park roads as transects. This study reported a death toll of 332 giant anteaters resulting directly from this fire and a surviving population of around 100 individuals a few months after the fire. Because population estimates were unavailable prior to the fire, its impact could not be fully assessed. Morevoer, the lack of continuous post-fire monitoring precludes any precise recovery estimates for this population.

This study purported to estimate the population density of the giant anteater in Emas National Park and determine the best method to monitor the park's anteater population. The resulting data may provide important information to better evaluate this population's recovery rate following the 1994 fire and pinpoint possible factors that may affect its numbers in the future. …