May 1993 NOTICIAS DE GALAPAGOS 21

International Congress of Systematic and Evolu- Wells, J.w. 1983. Annotated list of the scleractinian tionary Biology. Dioscorides Press, Portland, corals of the Galápagos. pp. 213- 295 in P.W.Glynn Oregon. and G.M. Wellington (eds.) Coral s and coral reefs Perry, R. 1984. Key environments: Galápagos. Per- of the Galápagos Islands. University of California gamon Press, New York. Press, Berkeley, California. Schatz, H. 1991. Catalogue of known species of acari Westheide, W. 1991. The meiofauna ofthe Galápa- from the Galápagos Islands (Ecuador, Pacific gos; a review. Pp. 37-74 in M.J. James (ed.) Ocean). International Journal ofAcarology 17:213- Galápagos invenebrates: taxonomy, biogeography, 225. and evolution in Darwin's Islands. Plenum Press, Schatz, H., and 1. Schatz. 1988. Arachnological re- New York. search in the Galápagos Islands (Ecuador) with Wicksten, M.K. 1991. Caridean and Stenopodid special reference to the Oribatida (Acari). Euro- shrimp of the Galápagos Islands. Pp. 147-156 in pean Association of Acarologists Newsletter M.J. James (ed.) Galápagos invertebrates: taxon- 1(2):4-10. omy, biogeography, and evolution in Darwin's Shear, W.A., and S.B.Peck. 1987. Millipeds (Diplopo- Islands. Plenum Press, New York. da) of the Galápagos Islands, Ecuador. Canadian Zullo, v.A. 1991. Zoogeography of the shallow-wa- Journal of Zoology 65:2640-2645. ter cirriped fauna of the Galápagos Islands and Shear, w.A., and S.E. Peck. 1992. Centipeds(Chilopo- adjacent regions in the tropical eastern Pacifico da) and Symphyla of the Galápagos Islands, Pp. 173-192 in M.J. James (ed.) Galápagos inver- Ecuador. Canadian Journal of Zoology 70:2260- tebrates: taxonomy, biogeography, and evolution 2274. in Darwin's Islands. Plenum Press, New York. Stork, N.E. 1988. Insect diversity: facts, fiction and Stewart B. Peck, Department ofBiology, Carleton speculation. Biological Journal of the Linnean University, Ottawa, Canada KlS 5B6. Society 35:321-337.

THE UNNATURAL COLONIZATION OF GALAPAGOS BY SMOOTH-BILLED ANIS (CROTOPHAGA ANI)

By: Peter R. Grant and Tjitte de Vries

The Galápagos are the most isolated Islands in the Possibly they flew across the 1,000 km of open eastern Pacific that have a clearly and wholly Amer- water from continental Ecuador. Harris (1973, 1982) ican terrestrial bird fauna. Smooth-billed Anis suggested an alternative, that the anis were introduced (Crotophaga ani) were first recorded on the Islands by farmers in the belief they would remove tics from in 1962. This was surprising since they fly soweakly. cattle. He pointed to their basically sedentary nature, Single individual s were seen on Isabela that year, on weak flight, and association with cattle as reasons for Santa Cruz 4 years later, and on Santiago in 1967 thinking they were introduced, while acknowledging (Harris 1973). None were seen again untilI980-81, that individuals do sometimes wander outside the when some appeared in the farmland of Santa Cruz normal range of a population. We have made a survey (Harris 1982). Since then a breeding population has of bird faunas on other eastern Pacific islands, and it become established on this Island, where at one time supports Harris' suggestion that their journey to numbers were estimated to be well over 5,000 birds Galápagos was not accomplished without human help. (Rosenberg 1987), and individuals have been seen on Crotophaga ani, or its close relative C. sulciros- many otherislands in theArchipelago. How did these tris (the Groove-billed Ani), is found on thecontinent cuckoo relatives reach the Galápagos? from Chile north to México, but neither occurs on 22 NOTICIAS DE GALAPAGOS No. 52

México's Revilla Gigedo Islands off Columbia. All failure to reach the island, or failure to colonize it by these islands are well isolated, being more than 300 establishing a breeding population once it has got km from the continent. Similarly, neither species of there. In the case of the ani, absence from most Pacif- anis has been recorded on the much less isolated Tres ic islandscan be exp1ainedin eitherway. Forexamp1e, Marías Is1ands, 80 km off western México, even the habitats on the Revilla Gigedo Is1ands and on though a complete list of breeding bird species has Cocos Island are very different from each other, and been established and a long 1ist of migrants and va- both might be unsuitable for anis even if they were grants has been thoroughly documented for these able to reach the islands naturally. However, some of islands (Grant and Cowan 1964). the islands lacking anis do have some agricultural The island in the eastern Pacific most isolated from 1and, or at least some cultivation of land associated main source populations on which anis (C. ani) are with human settlement, so for these islands coloniza- known to occur is Isla Gorgona, 55 km from the coast tion would appear not to be a problem. Anis may of Colombia (F. Koster, pers. comm.). The next most never have reached them. isolated island with anis is Isla Coiba. It is only 25 km Facts such as these lead us to conclude that the from the mainland of Panamá. Anis are restricted to presence of anis on the Galápagos cannot reasonably open cul tivated land and low thickets in the middle of be attributed to natural colonization following unaid- cleared land on the island (Wetmore 1957). On the ed immigration fram the continent. There is no mainland of Panamá the spread of this species from evidence that anis are capable of flying the enormous east to west was slow, and apparently it was made distance across water which would be required to possible by forest clearance and the artificial creation reach the Islands. We do not claim this is impossible, of savannahs (Wetmore 1968). only that it is highly unlikely. The alternative expla- Despite flying short distances and slowly over nation for the presence of anis on the Galápagos, that cultivated land, anis are capable of flight over water. they were introduced by humans, is much more like- In the Galápagos they have reached several well iso- ly.And from all that is known about the biology ofthe 1ated Islands including Genovesa, which is about 90 anis elsewhere, the success of the introduction (or km from the central Islands of Santa Cruz and San- introductions) was due to the clearing and cultivation tiago. They have done so apparentl y unaided although of land on Isla Santa Cruz. possibly boats have given them inadvertent help. It may be interesting to compare the ani with the In the Atlantic their presence on many islands in CattleEgret (Bubulcus ibis). Like the ani, this species the West Indies (Voous 1957, Lack 1976) and on was tirstrecorded on the Galápagos in the ear1y 1960s offshore islands of central America (Monroe 1968) (Harris 1982) and became cornmon and widespread certainly suggests they are capable of flying moder- in the 1980s. Harris (1982) refers to it as a regular ately long distances over water. Furthermore they visitor. A breeding site on southern Isabela was dis- have colonizedFloridarecently, and, unless they were covered in 1986 (Perez and Nowak 1987), and introduced, they must have flown a minimum dis- confirmed in 1987 (Vargas 1990). Also, like the ani, tance of 100 km from the Bahamas to get there (Lack it takes advantage of cultivated land and highland 1976). Only one among the numerous islands ofthe pampas with free-roaming cattle, particularly on West Indies, Jamaica, is more isolated (150 km), and southern Isabela and Santa Cruz. Unlike the ani, only one other pair of islands in theAtlantic with anis, however, it almost certainly arrived unaided. There is the Swan Is1ands (Monroe 1968), is more isolated no incentive to introduce it since it does not have the (200 km) than Jamaica. In all colonized areas, how- reputation of removing ticks from cattle. Moreover, ever, anis are almost entirely restricted to cultivated it has undergone a recent expansion globally and not land. just in the eastern Pacific, and its distribution is now It is well known that the absence of a species from virtually worldwide. It has the powers of long-di s- an island can be attributed to one oftwo causes: either tance flight that the ani lacks. May 1993 NOTICIAS DE GALAPAGOS 23

LITERATURE CITED Vargas, H. 1990. Present status of resident aquatic Grant, P.R., and I. MeT. Cowan. 1964. Areview of birds in lagoons near populated zones. Pp. 104- the avifauna of the Tres Marías Is1ands, Nayarit, 106 in CDRS Annual Report 1986-87. Mexieo. The Condor 66:221-228. Voous, K.H. 1957. The birds of Aruba, Curar;ao, and Harris, M.P. 1973. The Galápagos avifauna. The Bonaire. Studies on the Fauna of Curar;ao and Condor 75:265-278. other Caribbean Islands 7(29): 1-260. Harris, M.P. 1982. A field guide to the birds of the Wetmore, A. 1957. The birds ofIsla Coiba, Panamá. Galápagos. Collins, London. Smithsonian Miscellaneous Colleetions 134(9): 1- Laek, D. 1976. Island biology. University of Cali- 105. fornia Press, Berkeley and Los Angeles. Wetmore, A. 1968. The birds of the Republic of Monroe, Ir., B.L. 1968. A distributional survey of Panamá. Part 2.-Columbidae (Pigeons) 10Picidae the birds ofHonduras. Omithologieal Monographs (Woodpeekers). Smithsonian Institution Press, 7:1-458. Washington, DC. Perez, S., and B. Nowak. 1987. Por primera vez Peter R. Grant, Department of Ecology and Evo- anida garza bueyera en Galápagos? Carta Infor- lutionary Biology, Princeton University, Princeton, mativa, CDRS and SPNG, Santa Cruz, Galápagos New Jersey 08544-1003, USA. Tjitte de Vries, 20:4. Departamento de Biología, Pontificia Universidad Rosenberg, D. 1987. Nueva amenaza para las aves Católica de Quito, Ecuador. nativas. Carta Informativa, CDRS andSPNG, San- ta Cruz, Galápagos 21:4.

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