DUBLIX NATTTRAL HISTORY 30CIKTY. 1 7 



food, or renders it unattainable, or nearly so. The species, flying the 

 winter, travels south, finding in its course conditions pretty similar to 

 those which prevailed in its summer abode in more northern latitudes. 

 When at length it has reached a district (suppose Great Britain) in 

 which these conditions, or at least conditions compatible with its adult 

 existence, are permanent in the winter, it there abides until the in- 

 creasing heat of the spring renders its adopted home unsuited to it, or 

 at least to its future progeny. Again it takes up its journey, and 

 travels north, flying from the summer heat. Such a species arriving 

 liere in the winter, the Briton calls a winter migrant. A second species, 

 the house-swallow (A. nistica), rears its young in Britain. This duty 

 over, on the appearance of the British winter, it seeks in the milder la- 

 titudes of the south its winter quarters, returning again to the north 

 when these prove too hot to hold it. 



ISTow, it has been already shown that in the district Ijang east and 

 west of the area included within the normal migratory lines of each spe- 

 cies, there occur sub- areas which are nearly as suitable for the well- 

 being of such species as the districts contained within these limits : and 

 hence, if by any disturbing cause a migratory bird is driven out of its 

 usual course, it may in such sub-areas find a spot in which it can sub- 

 sist, and where it will probably remain until more favourable circum- 

 stances enable it to regain its course ; and if this divergence takes place 

 during its northerly migration, it may possibly breed here. Eemark- 

 able instances of this latter phenomenon are seen in Ireland among 

 southern migrants, in the golden oriole ( 0. galhula), blackcap warbler 

 (C. atricapiUa), hawfinch (C. vulgaris), crossbill {L. curvirostris), rose 

 pastor (P. roseus), hoopoe {U. epops), melodious willow wren {Sylvia 

 hippolais), stone plover {(JR. crepitans), dotterel (C. tnorincUus), and 

 possibly the grasshopper warbler {S. locustella) ; and in Great Britain, 

 in the golden oriole, hoopoe, rose pastor, &c. 



Taking it as proven that the migration takes place in a line north 

 and south — that it has fixed longitudinal limits, and that, through dis- 

 turbing causes, species occasionally transgress these limits and survive — 

 the occurrence of simimer European migrants in these isles is what 

 might have been expected. All that has occurred is this — the birds, in 

 their passage south, meeting with easterly gales, have been driven from 

 their course, and finding here localities suited to their habits, remain 

 either till spring, or till a favourable moment for continuing their south- 

 ern journey arises. 



The instances of the occurrence of such birds in Ireland in the winter 

 are more numerous than might be supposed from published records. I 

 have collected all I could come across either from my own researches or 

 from those of R. J. Montgomery, Esq., and Robert Warren, Esq., Jun., 

 of Bailina, kindly communicated to me by those gentlemen, and from 

 Thompson's " Eauna of Ireland," and have little doubt that they do not 

 represent a tithe of the instances in which this has occurred. I di\dde 

 them into : — Eirst, regular British summer migrants, unknown as such 

 in Ireland, though one or two have occurred during that season here ; 



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