Les hommes ont oublié cette vérité. Mais tu ne dois pas l'oublier, dit le renard. Tu deviens responsable pour toujours de ce que tu as apprivoisé.
Le Petit Prince, chap. 21

Saturday 13 April 2013

Socorro island's endemics and cats

Arnaud, G., A. Rodriguez, A. Ortega-Rubio, S. Alvarez-Cardenas. 1993. Predation by Cats on the Unique Endemic Lizard of Socorro Island (Urosaurus auriculatus), Revillagigedo, Mexico. Ohio Journal of Science, 93 (4): 101-103

During 1990 the distributions of the endemic lizard (Urosaurus auriculatus) and the feral cat (Felis catus) of Socorro Island were observed and scats of the last species were collected. A total of 46 cat scats were analyzed, showing that lizards were an important prey item, varying in frequency from 33.33% in February to 66.66% in November. Because of the impact of sheep (Ovis aries) on the natural vegetation and because of the impact of cat predation, we recommend that a plan be developed for the removal of exotic species and the restoration of natural vegetation to Socorro Island.

Jehl, J.R.& K.C. Parks. 1983. 'Replacements' of landbird species on Socorro Island, Mexico. Auk 100: 551-559.
The endemic dove Zenaida graysoni of Socorro Island, an oceanic island in the Pacific south of Baja California, became extirpated between 1958 and 1978 and the endemic mockingbird Mimodes graysoni diminished during the same years and was approaching extinction by 1981. The mainland mourning dove Z. macroura became established on Socorro between (probably) 1971 and 1978 and the mainland northern mockingbird Mimus polyglottos between 1978 and 1981. Superficially an instance of replacement of island endemics by mainland relatives through competitive exclusion, the case is actually more complicated. It is argued that extermination of the endemics was probably caused by predation by feral cats introduced in 1957 or later. There is no evidence of any actual competition between the pairs of species and their preferred habitats overlap only slightly. The nearly concurrent establishment of the 2 invading species, known to have occurred frequently as casual visitors to Socorro and other islands is attributed largely to the provision of fresh water made available as a result of human settlement. Simple comparison of island species lists compiled at intervals is an inadequate base for theories of island species turnover.

More info about Socorro's threatened birds:
BirdLife International (2013) Species factsheet: Zenaida graysoni. Downloaded from http://www.birdlife.org on 12/04/2013.
BirdLife International (2013) Species factsheet: Mimus graysoni. Downloaded from http://www.birdlife.org on 12/04/2013. 

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