This discussion was first published as part of the 2013 Red List update, but remains open for comment to enable reassessment in 2014.
Black-and-chestnut Eagle Spizaetus isidori has an extensive but narrow and altitudinally restricted linear distribution on the coastal ranges of north-central Venezuela (Carabobo and Aragua) and north-eastern Colombia (Santa Marta Mountains), and from the subtropical slopes of the Andes from Venezuela (Mérida and Perijá Mountains) through Colombia, Ecuador and Peru to west-central Bolivia and north-western Argentina (Fjeldså and Krabbe 1990, Thiollay 1994, Roesler et al. 2008). It is classified as Vulnerable under criterion C2a(i), on the basis of a small global population (approximately 1,000-2,499 mature individuals), with all subpopulations believed to number fewer than 1,000 mature individuals, and a continuing decline as a result of the destruction of its montane forest habitat.
It is thought to be rare and its status is very poorly known (Thiollay 1994, Ferguson-Lees and Christie 2001). The population in Venezuela has been estimated in the low hundreds (C. J. Sharpe in litt. 2003). Opinions on the population in Colombia differ: one population alone is thought to support a few hundred individuals (T. Donegan in litt. 2010), or the total population may be fewer than 100 adults (C. Márquez in litt. 2012). The population in Ecuador is thought to consist of a maximum of 200 mature individuals. The global population has been estimated to be both larger than 1,000 individuals (T. Donegan in litt. 2010, Y. Molina in litt. 2010) or fewer (H. Vargas in litt. 2012); complete surveys of this species throughout its range are needed to accurately quantify its global population.
However, recent sources suggest that no Andean country population contains more than 250 individuals (H. Vargas in litt. 2012). Additionally, the population is considered to be declining as a result of habitat loss (Thiollay 1994) and human persecution (H. Vargas in litt. 2012) throughout its range. If there is sufficient evidence to suggest that all subpopulations contain ≤250 mature individuals, the Black-and-chestnut Eagle would qualify for uplisting to Endangered under criterion C2a(i) of the IUCN Red List.
For the purposes of Red List assessments, subpopulations are defined as geographically or otherwise distinct groups between which there is little or no demographic or genetic exchange, i.e. typically one successful migrant per year or less.
Comments on the total population size, size of the largest subpopulation and likely population trends of this species are welcomed.
Ferguson-Lees, J. and Christie, D. A. (2001) Raptors of the world. London, UK: Christopher Helm.
Fjeldså, J. and Krabbe, N. (1990) Birds of the high Andes. Copenhagen, Denmark: Apollo Books.
Ridgely, R. S. and Greenfield, P. J. (2001) The birds of Ecuador: status, distribution and taxonomy. Ithaca, NY and London, UK: Cornell University Press and Christopher Helm.
Thiollay, J.-M. (1994) Family Accipitridae (Hawks and Eagles). In: del Hoyo, J., Elliott, A. and Sargatal, J. (eds.) Handbook of the birds of the world. pp. 52-205. Barcelona, Spain: Lynx Edicions.