This discussion was first published on Dec 22 2010 as part of the 2011 Red List update.
Initial deadline for comments: 31 January 2012.
Thick-billed Parrot R. pachyrhyncha is listed as Endangered under criterion C2a(ii) on the basis that its population numbers fewer than 2,500 mature individuals and is suspected to be declining due to the clearance and degradation of its habitat. The C2 criterion stipulates that certain conditions regarding sub-population structure must be met; for this species, all mature individuals are thought to form one sub-population (also suggested by the findings of Guerra et al. 2008).
Although the species’s breeding range is estimated at 600 km2, it does not qualify as threatened under the B criterion because it is considered to occur at more than 10 locations and habitat fragmentation is not regarded as severe, i.e. over 50% of suitable habitat in patches too small to support viable populations. The species, however, is regarded as having three main breeding sites (S. G. Maciel Ortiz in litt. 2010). Note that for the purposes of the Red List criteria ‘location’ defines a “geographically or ecologically distinct area in which a single threatening event can rapidly affect all individuals of the taxon present. The size of the location depends on the area covered by the threatening event and may include part of one or many subpopulations. Where a taxon is affected by more than one threatening event, location should be defined by considering the most serious plausible threat.” In considering whether a species is severely fragmented, note that the existence (or even a large number) of small and isolated patches is not sufficient to consider the taxon severely fragmented. For meeting this criterion, more than half of the individuals (or, more than half of the occupied habitat area) must be in small and isolated patches (IUCN 2001).
The latest population estimate known to BirdLife suggested that there were c.2,800 mature individuals, derived from the statement by Ortiz Maciel and Cruz Nieto (2004) that an estimate of up to 140 nests in the Bisaloachic-Cebadillas region represented c.10% of the total known breeding population. Not all of the nest cavities surveyed are used every year (M. A. Cruz Nieto et al. in litt. 2007), thus the number of mature individuals is estimated in the range 2,000-2,800. Recently, concerns have been expressed to us that this population estimate may be incorrect by an order of magnitude, as there are apparently fewer than 100 active nests each year (J. Gilardi in litt. 2010). Up-to-date estimates of both the total number of mature individuals in the population and the number of pairs that breed each year would be very useful. In addition, it is necessary to correct the population trend for a period of three generations. The rate of decline is currently estimated at 30-49% over 10 years; however, for the forthcoming assessment the population trend will be estimated over a period of the past 33 years (three generations). A rate of decline of at least 50% over three generations would make the species eligible for at least Endangered under the A criterion.
Guerra, J. E., Cruz-Nieto, J., Ortiz-Maciel, S. G. and Wright, T. F. (2008) Limited geographic variation in the vocalizations of the Endangered Thick-billed Parrot: Implications for conservation strategies. Condor 110: 639-647.
IUCN (2001) IUCN Red List Categories and Criteria: Version 3.1. IUCN Species Survival Commission. Gland, Switzerland and Cambridge, UK: IUCN.
Ortiz Maciel, S. G. and Cruz Nieto, M. A. (2004) Flying Emeralds. Birdscapes: News from International Habitat Conservation Partnerships. Spring/Summer 2004: 10-11.
The following document was sent by Pronatura on 16 February 2012: Rhynchopsitta pachyrhyncha Pronatura Feb12