Justification of Red List Category
The last record of an individual of this species in its natural habitat was in 1972. It is therefore classified as Extinct in the Wild. However, there are c.150 birds in captivity and reintroduction of the species is planned.
Fortunately, aviculture has prevented the extinction of the species, with captive populations held in around 30 institutions in the U.S.A., Europe and Mexico, with at least 70 institutions participating at some point in the captive breeding efforts since 1994 (J. E. Martínez-Gómez in litt. 2016). The European breeding programme for this endangered species has monitored the captive population for more than 30 years (J. E. Martínez-Gómez in litt. 2007). The captive population was thought to total several hundred birds, but hybridisation with Mourning Doves Z. macroura became a major problem in the U.S.A. in the 1990s (Martínez-Gómez et al. 2003), and it now appears that many of these U.S. birds are hybrids (J. E. Martínez-Gómez in litt. 1999, 2000, S. G. Stadler in litt. 2012). As a consequence of the occurrence of avian influenza in Europe in 2006, the Socorro Dove Project sent a total of 12 birds to Albuquerque Biological Park to form a second, independent reserve population nearer to the species's native country (S. G. Stadler in litt. 2012). The total captive population is currently estimated at approximately 150 individuals (J. E. Martínez-Gómez in litt. 2016). In 2013 and again in 2014 a number of birds were transferred to Mexico to form a national captive breeding flock ahead of efforts to eventually return the species to Socorro Island (H. Horblit in litt. 2013, J. E. Martínez-Gómez in litt. 2016).
This species has been extirpated from Socorro in the Revillagigedo Islands, Mexico. It was formerly common and observations in 1957 and 1958 gave no indication that it was declining. The last sighting in the wild was in 1972 (Baptista and Martínez-Gómez 1996), and all suitable habitat on the island has been surveyed subsequently without recording the dove (J. E. Martínez-Gómez in litt. 1999, 2000). Several individuals were taken during an expedition to the islands in 1925 and subsequently bred in the U.S.A., with some sent to Europe (Martínez-Gómez et al. 2003).
It was apparently commonest in forested areas above 500 m, dominated by Bumelia, Prunus serotina, Guettarda, Ilex, Psidium and Ficus. It was a highly terrestrial frugivore, and probably depended on an intact understorey of ferns and euphorbias.
The decline and extinction in the wild of this species has been attributed chiefly to predation by cats. However, it was thought that cats became feral on Socorro in the 1950s, but this date has now been revised to the early 1970s (J. E. Martínez-Gómez in litt. 1999, 2000). This suggests that other factors, such as human predation (Martínez-Gómez et al. 2003) and high levels of understorey grazing by sheep, may have been significant. Outbreaks of a permanent locust Schistocerca piceifrons swarm have occurred twice a year since 1994, resulting in damage to the leaves, flowers and fruit of indigenous forests, with at least 30 ha lost to defoliation so far, thus reducing the extent of prime habitat for the species (J. E. Martínez-Gómez in litt. 2007). Locust outbreaks may be favoured by the habitat degradation caused by introduced species (Song et al. 2006).
Conservation Actions Underway
The Revillagigedo Islands were declared a biosphere reserve in 1994 (Stattersfield et al. 1998, Martínez-Gómez et al. 2003). The European Association of Zoos and Aquaria recognised a breeding programme for the species, as initiated by Cologne and Frankfurt zoos (Germany) and the private interest group Wild Pigeons and Doves, as an official European Endangered species programme (EEP), in 1995 (Martínez-Gómez et al. 2003). Modern studbook software has been employed to assist with the genetic and demographic management of the captive population. Individuals have been distributed to zoos and bird parks in countries including Belgium, the Netherlands, U.K., Poland, Austria, Luxembourg, France, Spain, the Czech Republic and Germany (S. G. Stadler in litt. 2007, 2012). Of 672 individuals listed in the studbook by December 2010, 102 were known to be alive (S. G. Stadler in litt. 2012). Since 2006, following an extensive survey of the origin of the founding individuals of the EEP population, major software-based population genetic analyses have been conducted and recommendations for new pairs have been given by the EEP coordinator (S. G. Stadler in litt. 2007, 2012). A special breeding unit for the species has been opened at Marlow Bird Park, Germany (Martínez-Gómez et al. 2003). A proposal has been developed to reintroduce the species (Baptista and Martínez-Gómez 1996, Martínez-Gómez et al. 2003, S. G. Stadler in litt. 2012), along with a restoration programme for Socorro (Martínez-Gómez et al. 2003, Horblit et al. 2006). DNA fingerprinting has revealed extensive hybridisation with Z. macroura in the U.S.A., however it also showed a high degree of relatedness between the European population and pure individuals kept in California (Martínez-Gómez et al. 2003). As a result, the European population will be used for reintroduction efforts. The construction of breeding aviaries on Socorro began in August 2003 (Martínez-Gómez et al. 2003) and was completed by 2005 (Bell et al. 2005a). Resident populations of Z. macroura and Common Ground-dove Columbina passerina (Bell et al. 2005a) were screened in December 2003 and January 2004 to assess the presence of pathogens that might affect the reintroduction programme (Martínez-Gómez et al. 2003, Bell et al. 2005a, 2005b). Avian malaria and trichomoniasis were detected in both species, and as a result recommendations were put forward (Bell et al. 2005a, 2005b). In 2005, plans were outlined to control the locust outbreaks, restore native vegetation and assess the problem of erosion (J. E. Martínez-Gómez in litt. 2005). The arrival on Socorro of the first birds from the EEP was planned for June 2005 (Bell et al. 2005b), with the establishment of a breeding flock by June 2006 (Bell et al. 2005a, S. G. Stadler in litt. 2012). However, there have been problems with import restrictions and permits (J. E. Martínez-Gómez in litt. 2007). In the face of these restrictions a small insurance population was established in the U.S.A. in 2008 (H. Horblit in litt. 2007, J. E. Martínez-Gómez in litt. 2007), forming the basis for the return of the species to Africam Safari Zoo, Puebla, Mexico (S. G. Stadler in litt. 2012). Two groups of birds were transferred to Mexico in 2013 and 2014 to form the basis of a population for eventual reintroduction to Socorro (J.E. Martínez-Gómez in litt. 2016). Some control of feral cats has been undertaken on Socorro (B. Tershy in litt. 1999), and there were plans to eradicate cats in 2009 at the earliest (B. Tershy in litt. 2007). Reports that rats have recently colonised Socorro have proved to be unfounded (J. E. Martínez-Gómez in litt. 1999, 2000). The sheep population was been reduced to c.300 by the Mexican navy (J. E. Martínez-Gómez in litt. 2007). A programme to eradicate feral sheep from Socorro was conducted from 2009 to 2012 (Ortíz-Alcaraz et al. 2016). Cat eradication efforts are ongoing (J.E. Martínez-Gómez in litt. 2016). Techniques to grow four endemic tree species from Socorro have been successful, with 117 tree seedlings planted on the island. These restored areas will be important when birds are eventually released back onto Socorro (J.E. Martínez-Gómez in litt. 2016). The species is included on the 'Watch List' of the State of North America's Birds as a species of high conservation concern (NABCI 2016).
26.5-30.5 cm. Medium-sized, principally terrestrial dove. Male has deep cinnamon head and underparts, with black streak on lower ear-coverts, blue-grey nape and iridescent pink neck patch. Dark brownish upperparts, boldly spotted with black on scapulars, tertials and inner wing-coverts. Dark grey flight feathers. Dark brown central tail, outer feathers grey with black subterminal band and grey tips. Female duller, with smaller blue-grey nape and pink neck-side patches. Juvenile similar to female, except coarse breast streaking and cinnamon-buff tips to upperparts feathering. In all plumages has pale blue orbital ring, pinkish legs and dark grey bill with reddish-pink base. Similar spp. Larger and more heavily built than Mourning Dove Z. macroura, and song very different. Voice Hoarse cooing song, wah-ah ah ah ah ahh-ah.
Text account compilers
Benstead, P., Capper, D., Isherwood, I., Sharpe, C J, Taylor, J., Khwaja, N., Ashpole, J, Martin, R
Tershy, B., Horblit, H., Martínez-Gómez, J.E., Stadler, S.
BirdLife International (2020) Species factsheet: Zenaida graysoni. Downloaded from http://www.birdlife.org on 29/09/2020. Recommended citation for factsheets for more than one species: BirdLife International (2020) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 29/09/2020.