Birds. 



6533 



summer visitors. I have myself seen a wheatear upon the banks of 

 the Royal Canal in the month of December. The hoopoe has more 

 than once been killed in February, and many of the scarcest occasional 

 visitors to Ireland, as well as Great Britain, have been met with 

 during the autumn and winter months : as examples, the spotted 

 eagle, griffon vulture, spoonbill, avocet, blackwinged stilt, ibis, 

 whiskered and black terns may be quoted ; to which perhaps might 

 be added White's thrush and the Sabine snipe (if a good species), and 

 the two African birds, spotted cuckoo and goldvented thrush, both 

 obtained in winter. Nor are the instances in which some of these 

 birds have been noticed in the spring or summer sufficient to 

 invalidate those above quoted, since it is only here wished to prove 

 the occasional occurrence in Great Britain, during late autumn and 

 winter, of species that come from the South-east and East; and we 

 need not be surprised to find birds from any quarter visiting us at either 

 of the periods of the general migratory movement, it being well known 

 that a few species have, both in spring and autumn, wandered to our 

 shores from America* as well as Africa. 



But indeed when we consider the differences presented by the 

 remarkable contrast between the climates termed e< maritime" and 

 " continental" by geographers, the former being distinguished by its 

 mild temperature in winter, and more favourable from the moisture of 

 its air to a continuance of insect-life at that season, — while the 

 continental is equally rigorous, — why should not birds by instinct be 

 aware of these differences ? 



The recent occurrence in Sussex of Sylvia galactotes, a bird of 

 quite southern distribution on the Continent, sufficiently shows that 

 the line of autumnal migration does not lie at all arbitrarily North 

 and South ; but, to a great extent, at right angles to the " Isotherms " 

 of winter temperature, which run in a direction of N.W. and N.N.W. 

 in Central and Western Europe, and migration must therefore take 

 place in a line from the N.E. and E. to W.S.W. and W. With 

 future observation I feel little doubt that the streams of migration 

 may hereafter be laid down in a manner analogous to that of the 

 ocean and air currents ; and that the laws which govern those streams 

 will be found to depend upon the nicely balanced influences of — 

 1st, prevailing winds; 2nd, physical features of mountain chains and 



* At least eight Incessorial and nine Grallatorial birds have crossed the Atlantic ; 

 and, if we may trust all the notices, three species of woodpeckers, which, like the 

 belted kingfisher, are not generally credited with enduring powers of flight. 



