120 



tion — a process taking a lon^- period of time to bring about — to aid us in deciding 

 whether any species is autochthonous or not ; even had such changes occurred, 

 these might have been in the descendants of an early immigrant. Is there 

 anything else that may help us in deciding? VVe may possibly get some help 

 by ascertaining whether the species of land birds present also occur on the 

 adjacent mainland, and, if so, whether they are numerous there and what are 

 their habits. If an island species is not present on the mainland, we may infer 

 that the species is autochthonous or an early immigrant, i.e., an immigrant at a 

 period when the species also occurred on the mainland, though it had since died 

 out. Again, if the species in question is relatively rare on the adjacent coast, 

 if it does not congregate in little flocks, and if in its habits it is disinclined to 

 fly across open spaces and so be caught by a strong wind and blown to sea, then 

 there is little likelihood of an individual becoming an tniwilling immigrant to 

 this distant island, and still less likelihood of a pair of birds, of opposite sexes, 

 reaching it within a year or so of each other so as to mate and have offspring. 

 Unfortunately a consideration of these several aspects still leaves the matter 

 open. 



In October, 1909, members of the Australasian Ornithologists' Union visited 

 Eyre Peninsula and held a camp at Wanilla, some 50 miles north-west of Port 

 Lincoln. From here excursions were made as far as the south-east end of the 

 Great Australian Bight. The birds noted are recorded by Hall (The Emu, 

 ix., 1909-10. p. 123). In this list appear the Raven (Coronc austral is), the Red- 

 cap Robin. EfiJithiaiiiira albifroiis, FacJiyccphala pecioraUs, \\'elcome Swallow. 

 Zosterops, three species -of Wood-Swallows, Ncophema petrophila, Starlings, 

 and Sparrows. A Bronze Cuckoo does not appear, but its omission does not 

 mean that it does not occur. We thus see that the birds found on the islands 

 occur on the mainland nearly opposite, assuming that the Wood-Swallow seen 

 belongs to one of the three species noted (if so, Artamus pcrsonatus). 



Let us consider these birds in detail. The Crow, or Raven, is a powerful 

 flier, and might possibly deliberately visit the island and, at any rate, might 

 easily be blown there. Zosterops frequently congregates in little flocks, and 

 these may traverse open spaces. Flocks might thus be easily blown to sea, and 

 the sudden irruption of these birds in New Zealand a number of years ago 

 is believed by many to have been due to a flock having thus been wind-borne. 

 At Willis Island, in the Coral Sea, about 250 miles from Cairns, two birds, 

 believed from the description to be Zosterops (The Emu, xxii., January, 1923, 

 p. 186), are recorded as "strangers." Zosterops may thus be taken to be a bird 

 liable in its habits to be blown to sea and to survive over long stretches of ocean. 

 With strong north and north-east winds it might easily, therefore, from time to 

 time be blown from its feeding haunts near open coasts to the Pearson Islands. 

 If any of the present birds cart claim to be descendants of individauls left behind 

 originally, it may safely be assumed that over the centuries this blood has been 

 diluted again and again by new arrivals. 



EpJithianura albifrons was one of the commonest birds on the islands. Its 

 tendency to inhabit open spaces, often near the sea, covered with low shrubs 

 such as samphire, and its congregation into small flocks, would render it, like 

 Zosterops, liable to being frequently blown to sea. 



Welcome Swallows, besides frequenting the neighbourhood of human dwell- 

 ings, caves, and overhanging rocks, are also found on rocky coasts, such as 

 those west of Rosetta Head, at Encounter Bay. In such situations they doubtless 

 find suitable nesting sites in the breeding season. On Pearson Islands they 

 were seen on a similar rocky coast and flying to and fro amongst overhanging 

 masses of granite near the highest point on the main island. Their powers of 

 flight and frequent coast habitat account for their presence. 



