The Floreana Mockingbird, Mimus trifasciatus, is currently listed as Critically Endangered on the basis that it had a tiny population size. The species is found only on the islands of Champion and Gardner-by-Floreana in the Galapagos, Ecuador (EOO currently estimated as 17km2), having gone extinct on Floreana at some time between 1868 and 1880 (Curry 1986; Steadman 1986). A Conservation Action Plan was developed in 2007 (Charles Darwin Foundation 2008) and a new one produced in 2013 (Ortiz-Catedral 2013); with reintroductions to Floreana planned (Charles Darwin Foundation 2013).
Its extinction on Floreana was likely a result of depredation by invasive species such as feral cats, dogs and Black Rats (Rattus rattus), as well as goats causing habitat loss (Harris 1973; Curry 1986; Grant et al. 2000). Black Rats are present on other nearby islets, and their introduction to either of the two remaining populations is a continuing threat (G. Jiménez-Uzcátegui in litt. 2007). There are a range of other potential threats facing this species; for instance the Smooth-billed Ani (Crotophaga ani) is known to predate other bird species and has been seen on both islands where the mockingbird persists (G. Jiménez-Uzcátegui in litt. 2007); the parasitic fly Philornis downsii has been recorded in mockingbird nests (Wiedenfeld and Jimenez-Uzcategui 2008; Charles Darwin Foundation 2013); and additionally climate can have a large influence on the species with dry La Niña years leading to increased adult mortality, and the increasing frequency of dry years being put forward as the cause of large population fluctuations (Grant et al. 2000; D. Wiedenfeld in litt. 2010). Finally, disease is another threat to this species as avian pox is thought to lead to mortality (see Grant et al. 2000) and transmission of disease from introduced chickens could also pose a threat (Deem et al 2012).
The population declined on both of the islands where it remained extant such that between 2003 and 2008 the population on Champion varied from 20-52 individuals (only 12 mature individuals in 2006) (Jiménez-Uzcátegui et al. 2011); and on Gardner-by-Floreana the population was estimated to have varied between 65 and 179 individuals (estimated only 29 mature individuals in 2007) (Jiménez-Uzcátegui et al. 2011). The overall lowest population size within this time period was in 2007 when it was estimated that only 46 adults remained (Jiménez-Uzcátegui et al. 2011). However, the population size has since increased, aided by rains triggering increased breeding activity, although large fluctuations could still occur as a result of climatic conditions (Hoeck 2009, Charles Darwin Foundation in litt. 2009, D. Wiedenfeld in litt. 2010). As of 2012 the population was estimated at 756 individuals (roughly equivalent to 504 mature individuals and placed in the range of 250-999 mature individuals), with the global population >50 mature individuals possibly since 2008 (when the global population size was estimated at 107 mature individuals). Therefore, the population no longer meets the criteria for listing as Critically Endangered, with the population size having been >>50 mature individuals for over 5 years, and so the species warrants downlisting. However, its highly restricted range, being found at only 2 locations with the possibility of climate-induced extreme (at least ten-fold) fluctuations in the number of mature individuals, means that this species would still warrant listing as Endangered under criteria B1ac(iv)+2ac(iv).
We welcome any comments regarding this proposed downlisting.
Charles Darwin Foundation. 2008. Action Plan to Save the Floreana Mockingbird of Galapagos.
Charles Darwin Foundation. 2013. Reintroduction of the Floreana Mockingbird Mimus trifasciatus. Charles Darwin Foundation.
Curry, R. L. 1986. Whatever happened to the Floreana Mockingbird? Notícias de Galápagos 43: 13-15.
Deem, S.L., Cruz, M.B., Higashiguchi, J.M. and Parker, P.G. 2012. Diseases of poultry and endemic birds in Galapagos: implications for the reintroduction of native species. Animal Conservation 15: 73-82.
Grant, P. R.; Curry, R. L.; Grant, B. R. 2000. A remnant population of the Floreana mockingbird on Champion Island, Galápagos. Biological Conservation 92: 285-290.
Harris, M. P. 1973. The Galápagos avifauna. Condor 75: 265-278.
Hoeck, P. 2009. Encouraging news from 2009 Floreana Mockingbird survey – The dodo blog, Durrell Wildlife Conservation Trust.
Jiménez-Uzcátegui, G; Llerena, W.; Milstead, W. B.; Lomas, E. E.; Wiedenfeld, D. A. 2011. Is the population of Floreana Mockingbird Mimus trifasciatus declining? Cotinga 33: 1-7.
Ortiz-Catedral, L. 2013. Action Plan for the Floreana Mockingbird Mimus trifasciatus 2012- 2015. Charles Darwin Foundation and Durrell Wildlife Conservation Trust.
Steadman, D. W. 1986. Holocene vertebrate fossils from Isla Floreana, Galápagos. Smithsonian Institution, Washington, D.C.
Wiedenfeld, D. A.; Jiménez-Uzcátegui, G. A. 2008. Critical problems for bird conservation in the Galápagos Islands. Cotinga: 22-27.