278 CORVIDvE. 



The second discrepancy of habit which must be noticed 

 is one that will weigh heavier with many naturalists, and yet 

 it seems really to have but little significance. Throughout 

 the greater part of the British Islands the Black Crow, where 

 it occurs, is mostly a summer- visitant, while the Grey Crow, 

 in England at least, is, as a rule, an autumnal immigrant, 

 appearing regularly in the fall of the year, and disappearing 

 as regularly in spring. But then we have to consider the 

 general principle of migration. Whatsoever its cause may be 

 and howsoever it may be effected, its process is undisputed. 

 In the northern hemisphere as summer wanes all birds 

 subject to its influence move in a generally southward 

 direction. Now Crows, whether Black or Grey, notoriously 

 belong to this category and shift their quarters accordingly. 

 In Great Britain, and to a certain extent elsewhere, the 

 Black Crow occupies a more southern range than the Grey 

 Crow. This relative position is preserved irrespective of 

 season. Each follows the sun towards the equator and 

 each moves northwards as the sun returns towards the pole, 

 so that both are impelled by precisely the same movement*. 

 We know how with many kinds of birds our native stock 

 emigrates more or less entirely towards autumn, and its 

 place is taken by an influx of northern strangers. In 

 some species the most practised eye can detect no difference 

 between its indigenous and its foreign members ; but in 

 others such a difference is easily discerned. In the Crow 

 the difference is wider perhaps than in any, but the difference 

 is only of degree, it is quantitative and not qualitative. 

 Hence, while the discrepancy affords us no proof that the 

 Grey and Black Crows are specifically distinct, it furnishes no 

 good ground for asserting that they are specifically identical. 



In other respects the habits of the two forms defy differ- 

 entiation. Their food, cries and mode of nidification, their 

 rapacity, wariness and conduct generally are absolutely alike ; 

 and their geographical distribution, which offers many points 

 of interest, alone remains to be considered. In the British 

 Islands it may be said that the Black Crow breeds, if per- 



* This bas been admirably put by Mr. Hancock (ut supra). 



