Avian Predation on Tortoises in Israel



Faculty of life Sciences, Tel Aviv University, Ramat Aviv 69978, Israel
e-mail: geffene@post.tau.ac.il

        Formerly, the bird most commonly known to prey on chelonians in Israel was the Egyptian vulture, Neophron peronopterus.  Its thin bill enables it to extract the contents of the tortoises’ shells.  However, the extent of this predation has always been insignificant, and since the 1950s when the population of the Egyptian vulture decreased considerably, predation has become even less significant. The serpent eagle, Circaetus gallicus, which feeds almost exclusively on reptiles, occasionally preys on small tortoises, but this predation is negligible.
        Another, much more extensive predation was discovered in April 1982, when a pair of brown-necked ravens, Corvus ruficollis, was flushed from an isolated tree on a broad, open plain in the western Negev.  Each raven dropped a young tortoise, one partly eaten but still alive, the other almost a completely empty shell.  Under this same tree, almost 40 empty shells of young tortoises were found in all stages of predation—from freshly dismembered to completely dried out.  Apparently, the pair of ravens regularly used this tree from which to feed upon young tortoises collected from the area.  About one third of the shells were of Testudo kleinmanni; the remaining were of Testudo graeca (Mendelssohn, 1982).                        
        During a survey of Testudo kleinmanni, it was found that adults of the species are also eaten.  Tortoises were preyed upon from both front and rear openings, and in some cases, the two movable rear lobes of the plastron had been deflected or removed.
        Predation by corvids is likely to increase considerably in the near future.  Two species, the brown-necked raven (Corvus ruficollis) and the hooded crow (Corvus corone sardonius), are undergoing a population explosion as a result of increased numbers of open garbage dumps and other food sources created by human activities.  C. ruficollis is a desert species, penetrating the range of T. kleinmanni from the east and south, whereas C. corone sardonius has a Mediterranean distribution and invades the area from the north and west.  Both species seem able to coexist in the same area, and both feed on small tortoises.  Formerly, no corvids existed within the range of Testudo kleinmanni and there was no problem with avian predation.  Following agricultural and urban development, however, both species of corvids have expanded into the area and now exert considerable predation pressure.  In addition, population densities of both Corvus species are now significantly higher.  The hooded crows may presently number up to 17 breeding pairs per km², and breeding success is generally good (Erez, 1990).  It is unknown if these high densities of crows affect the Testudo graeca populations.  Adult tortoises seem to be immune to crow attacks, but small individuals are certainly vulnerable, although they are rarely seen as they inhabit dense vegetation.

Literature Cited:

Erez, A.  1990.  On the breeding ecology of the hooded crow (Corvus corone sardonius) in Israel.  M.S. thesis, Tel Aviv University, Ramat-Aviv, Israel.
Mendelssohn, H.  1982.  Egyptian tortoise.  In The IUCN Reptilia-Amphibia Red Data Book. Part 1. Testudinidae, Crocodylia, Rhynchocephalia (B. Groombridge, comp.), pp. 133–136.  IUCN, Gland, Switzerland. xiii + 426 pp.

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