to lnhaca Island, Mo~ambique. Jackass penguins do not usually occur far off shore. The minimum total breeding population in 1978/79 was estimated to be approximately 134000 birds. Numbers halved between 1956 and 1978 alone as a result of collapses in the South and South West African pilchard populations. Numerical decreases at Possession and Dassen Islands were particularly severe. Prior to 1956 numbers had also decreased, primarily because of large collections of eggs. Sealing activities and guano harvests may also have influenced trends. Only colonies at the periphery of the breeding distribution have increased numerically in recent times, and such increases appear to be related to the availability of suitable prey. Although the species breeds in captivity and is unlikely to become extinct, its continued survival in the wild probably relies on the continued good state of the pelagic fish resources. Die Kaapse pikkewyn, endemies in suider-Afrika, is die enigste lid van die Sphenisciformes wat tans in Afrika broei. Die broeiverspreiding van die spesie strek van Sylvia-heuwel, Suidwes-Afrika (Namibie), tot by Voeleiland, Algoabaai, Suid-Afrika. Die nie-broeiverspreiding strek van Sette Cama, Gaboen, tot by Inhacaeiland, Mosambiek. Kaapse pikkewyne kom gewoonlik nie ver van die kus af voor nie. Die totale broeibevolking is in 1978/79 op 'n minimum van ongeveer 134 000 geraam. Net tussen 1956 en 1978 is getalle gehalveer as gevolg van ineenstortings in die Suid-en Suidwes-Afrikaanse sardynbevolkings. Veral by Possession-en Dasseneiland was die getalsvermindering drasties. Voor 1956 het getalle ook afgeneem, primer vanwee grootskaalse eierversameling. Robbejagbedrywighede en ghwano skrapery kon ook 'n uitwerking op tendense gehad het. Die afgelope tyd het net kolonies aan die buiterand van die broeiverspreiding in getalle vermeerder, en sodanige vermeerderings hou blykbaar verband met die beskikbaarheid van geskikte prooi. Hoewel die spesie in gevangenskap broei en uitsterwing onwaarskynlik is, hang die voortbestaan daarvan in die natuur waarskynlik af van die voortgesette goeie stand van die pelagiese vishulpbronne. •.Birds as large as ducks. they do notfly because they do not havefeathers on their wings. We killed as many of them as we desired and they bray like asses"-Vasco da Gama in 1497.

, Bird (Port Elizabeth) and Bird (Lambert's Bay) Islands respectively. Gannets have not been reported at Seal Island since the late 17th century. On the west coast of Africa the Cape gannet is a regular nonbreeding winter visitor as far north as 4°20'N 6°00'E, but west of 6°E it is rare. On the east coast of Africa it is a common winter visitor as far north as Delagoa Bay, but farther north it is rare. Within its normal range the Cape gannet seldom occurs farther off shore than 100 km; it hardly ever moves inland. Aerial censuses of Cape gannets at breeding islands in

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Ecologists have long attempted to predict the success of species that are introduced into foreign environments. Some have emphasized qualities intrinsic to the species themselves, whereas others have argued that extrinsic forces such as competition may be more important. We test some of the predictions made by both the extrinsic and intrinsic hypotheses using passeriform birds introduced onto the island of Saint Helena. We found direct evidence that extrinsic forces are more important predictors of successful invasion. Species introduced when fewer other species were present were more likely to be successful. In a direct test of the alternative hypothesis that intrinsic forces play a more prominent role in success or failure, we found a tendency for species which successfully established on Saint Helena to be also successful when introduced elsewhere. However, the vast majority of species unsuccessful at establishing on Saint Helena had probabilities of success outside Saint Helena of 50% or greater, making this result somewhat equivocal. Finally, we found no evidence to support the hypothesis that species that are successful early are those that are intrinsically superior invaders. These results are consistent with similar analyses of the introduced avian communities on Oahu, Tahiti, and Bermuda.

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