BRITAIN'S BIRDS AND THEIR NESTS. 237 



there is one important objection. When interbreeding 

 occurs, obvious hybrids are sometimes produced ; but it 

 seems to be more usual for half the brood to turn out 

 Black and half Hooded. This implies a considerable 

 amount of ' fixity '' of the characteristics in question, and 

 places the divergences on a different level from ordinary 

 colour ' phases,"* where such an endless series of intermediate 

 forms exists that it is difficult to find two individuals alike, 

 and impossible definitely to lay down any hard-and-fast 

 types. The fixity of the difference seems to make the 

 birds more than colour ' phases '' ; but still the degree of 

 difference may be so slight as to make them something 

 less than species — namely, races or sub-species. This, 

 however, raises the academic question as to what consti- 

 tutes a ground for specific separation. Into that we 

 cannot enter ; for convenience in treatment we have ad- 

 hered in this work to the usual custom of retaining the 

 specific distinction and nomenclature. 



In north-eastern Europe the Hooded Crow attains an 

 abundance not known within our area, and flocks of 

 countless thousands pass westward and southward on 

 migration. As with many Birds-of-Prey, the rarity of 

 systematic game - preserving is responsible for the more 

 prosperous circumstances of Crows and others on the 

 Continent. Both Birds - of - Prey and Crows, however, 

 themselves become 'game,' a frequent and interesting 

 method of shooting them being that of taking cover 

 at the edge of some open space in which is tethered 

 as a decoy an Eagle -Owl or a Snowy Owl. In East 

 Prussia and elsewhere, the natives of some out-of-the- 

 way districts take great numbers of Hoodies every autumn, 

 and preserve them for winter food. 



