A RARE WARBLER. 



47 



never found its nest. In adults the plumage is brightly 

 coloured, being yellowish olive-green and a clear lemon- 

 yellow below. Above the eye there is a thin streak of 

 yellow, and a crescentic spot of the same colour below 

 it. A few very faint olive-grey streaks are seen on the 

 sides of the flanks'. It is about the size of a canary. 



There is another warbler called the prairie-warbler 

 {D. discolor), which has its" home in the United States, 

 and only visits the West Indies and occasionally Swan 

 Island and the Caymans in the winter time. Although 

 very similar to the vitelline warbler, it is smaller * and 

 has also distinct and constant di£ferences in its plumage, 

 which render it easy for the expert to recognise the 

 two birds as distinct species. We may therefore regard 

 the vitelline warbler as an offset, or insular race, of the 

 more dominant and continental prairie-warbler. 



It is very difficult, and even if we had the ability, it 

 would take too much space here, to formulate a satis- 

 factory explanation of why and how an offset from a 

 dominant and migratory species, like the prairie-warbler, 

 should have come to lead an isolated and non-migratory 

 existence, as we see this Swan Island race has done. The 

 subject is bound up with the complicated one of migration 

 and all its problems. But, at any rate, we have an indica- 

 tion, although it is not an explanation, of how new species 

 or sub-species may come to have their first inception and 

 lose their migratory habits in the case we have quoted 

 above of the myrtle-warbler. We might quote another 

 instance in the case of the migratory American " redstart 

 flycatcher " (Setophaga ruticilla), which only lately appears 

 to have become entirely resident in the island of Dominica ; 

 or again of Dendroica dominica and D. tigrina which are 

 said to breed occasionally in Jamaica ; of the blue-winged 

 teal (Querquedula discors) : and the spine-tailed duck 

 (Erismatura jamaicensis), both of which have become 

 permanent residents in the Grenadines. Altered con- 

 ditions of climate and environment, together with the 



♦ A point worth noting. 



