Renard du Brésil

Only two studies have previously estimated population densities of the Hoary Fox. Rocha et al. (2008) used linear transects at two locations in Mato Grosso and estimated 1.21 individuals per km² in an area covered by shrub savannah and 4.28 individuals per km² in an exotic grass pasture. However, these estimates should be cautiously interpreted since it is possible that the difference in density is biased by: i) the species' detectability in the different environments, and ii) the timing of sampling in different reproductive seasons. The 4.28 density was estimated in the second semester, when foxes are known to be denning and foraging with puppies together, and this may have overestimated density at the pasture site. Rezende (2018), using capture-recapture models accounting for imperfect detectability, estimated 0.41 individual per km² in a fragmented area comprising a matrix of exotic pastures in south-eastern Goiás. In the same region/population, Lemos and Azevedo (unpublished data) registered offspring mortality greater than 50% in cohorts monitored during 12 years, with potentially negative demographic impacts.

To estimate the population size of the Hoary Fox, the total area of suitable habitat was determined taking into account remnants of Cerrado habitats (grassland, savannah, and other non-forest), and 50% of the area of pastures, within the species’ current range, yielding an area of approximately 120,000 km². Considering the limited information on density for the species in disturbed and natural habitats (0.41 individual per km², Rezende 2018; 1.21 individuals per km², Rocha et al. 2008), the habitats known to be used and the anthropogenic threats across most of the range, it was estimated that the Hoary Fox population might be approximately 49,200-96,000 individuals (based on a mean density of 0.8 individual per km²). Number of mature individuals may vary according to species life stories, degree of habitat specificity, mortality rates, and how isolated subpopulations are. There are no available data on the number of mature individuals among different Hoary fox subpopulations. From a monitored subpopulation of Cumari, south-eastern Goiás, not all adults were able to find a mate and breed annually, and mortality of adults and dispersing young was high. Breeding males and females represented about 20-25% of monitored individuals annually (Lemos and Azevedo, pers. obs). On the other hand, genetic data obtained from Cumari and a second subpopulation from Araguari, western Minas Gerais, suggest high genetic diversity of individuals (He = 0.816, Silva 2015), despite the high degree of human disturbance in sampled areas. On a wider phylogeographic perspective, Garcez (2019) also infers that the population of Hoary Foxes is structured in only one population along Brazil, not showing signs of isolation or fragmentation. Therefore, considering 20-25% of the population is capable of reproducing, the high mortality rates of adults and dispersing young, and the low densities registered, the number of mature individuals is estimated to range between 9,840 and 19,200 mature individuals.

Considering the joint impacts of ongoing loss of habitat, road-kills, persecution, killing and transmission of diseases by domestic dogs, retaliation for the alleged predation of domestic fowl, high mortality of pups/juveniles in different populations along unprotected areas, and that this is common throughout the species distribution, it is not unreasonable to estimate that in 12 years (three generations) a decline of at least 10% of the population could occur.