The Vertebrate Fauna of Houtman's Abrolhos (Abrolhos Islands), Western Australia.

Abstract

SUMMARY. Mammals.—The two indigenous species of Mammals are only found in the Wallaby Group, the Wallaby on both the large islands, the Rat, as far as is known, only on East Wallaby Island. The latter is probably, and the former certainly, subspecificailly distinct from the mainland species. Snakes.—The three species of snakes do not appear to differ from the mainland forms. At present two have been found only on West Wallaby Island and the third on East Wallaby Island. Lizards.—-Four families are represented by some 19 species. The seven species of Geckonidae iire only known from the Wallaby Group, the two species of Pygopodidae only from West Wallaby Island, and the single species of Agamidae from the Wallaby Islands and North Island. The Scincidae are represented throughout the group, though we only met with the smaller species of Lygosoma outside the Wallaby Group; one of the larger forms, Egernia stokesi was, however, formerly plentiful on Rat Island. Froas.—Nothing is known no to the habitat of the two species recorded from the group. Birds.—of the 12 land-birds recorded from the Abrolhos, four Kestrel, Robin, Song-Lark, and Pipit) are certainly only casual visitors, five others (Rail, Crake, Kingfisher, Swallow, and White-eye) are probably visitors From the mainland, though all but the Crake and Kingfisher have been known to breed; the remaining three are almost certainly residents. Of these, the Pigeon and the Quail are found in the Wallaby Group and on North Island, the Scrub-Wren only on the Wallaby Islands. The two latter are subspecifically distinct from the mainland forms. Looking now of the different groups of islands we find that West Wallaby Islad has two snakes and two slow-worms confined to it, East Wallaby Island has one snake and one rat confined to it, whilst the two Wallaby Islands possess subspecies of a wallaby and a bird peculiar to them. The Wallaby Islands, with North Island, possess also one lizard and two birds not found in the other groups, one of the birds being a subspecies peculiar to the group. This distribution strengly suggests that the whole land-fauna of the group has been derived from the Wallaby Islands *. One of the chief features of the weather on the Abrolhos is the prevalence during the summer of “southerly busters,” estremely strong southerly winds. The presence of the two birds on North Island is thus easily accounted for, and it, is noteworthy that the one lizard which habitually climbs bushes is the one which has managed to reach that island. Doubtless at times the Lushes on the sand-hills which it frequents are blown into the sea, and occasionally reach North Island. The fact that the smaller skinks are found on many of the small sandy islets seems to show that the sea is no great burrier to their distribution. Probably their eggs are not damaged by floating in sea-water for some time. The larger Spiny-tailed Skink, Egernia stokesi, is a favourite food of the Sea-Eagles, and it is possible that individuals may be captured by them on the Wallaby Group and coppied to that Island, and if one occasionally escaped this would account for their presence on that group. A striking feature of the Abrolhos land-fauna is its southern character. Our knowledge of the distribution of animals in Western Australia is perhaps not sufficient to allow us to be dogmatic on the point, but there is every indication that when the islands were peopled from the mainland the fauna of the Geraldton district must have approximated much more than it does now to that of the extreme south-west. The range of Macropus eugenii does not now extend much north of Perth, whilst Epimys fuscipes is only known from the south coast and the islands of the Recherche Archipelago. Ortygodes varius and Cosmopelia elegans are not recorded from farther north than the Moore River, though it is not improbable that they may occur; Porzamoidea plumbea is not recorded from north of Perth. The most northerly record that I know for Denisonia coronata and for Egernia whitei, “Perth,” is less than 30 iniles north of Perth. Lygosoma richardsoni is known only from the Abrolhos. The remainder of the species are found farther north on the mainland, but there is not one of them which is not found in the south-west.