. Britain's birds and their nests . t on the ground amongthe heather, or in some other unusual place. In themild southern region of Ireland, also, the Hoodie issome weeks earlier in its nesting operations. The eggsof the Gray Crow are said to have a tendency to belonger in shape and paler and brighter in colour thanthe others, but the clutches are, as a rule, indistinguish-able. The notes of the two Crows are thought to bedistinct by many who know both well. If the Carrion-Crows note be syllabled as a harsh corrr, the Hoodiesmay be described as a more open caiTr. Both arequite distinct from th
. Britain's birds and their nests . t on the ground amongthe heather, or in some other unusual place. In themild southern region of Ireland, also, the Hoodie issome weeks earlier in its nesting operations. The eggsof the Gray Crow are said to have a tendency to belonger in shape and paler and brighter in colour thanthe others, but the clutches are, as a rule, indistinguish-able. The notes of the two Crows are thought to bedistinct by many who know both well. If the Carrion-Crows note be syllabled as a harsh corrr, the Hoodiesmay be described as a more open caiTr. Both arequite distinct from the much less harsh cah or * cawof the Rook, When all is said, there is practically nogreat difference of any kind between the two Crowsexcept that of plumage coloration, and that is moreconspicuous than important. For this reason, and because the two kinds interbreedfreely on all their frontiers, many deny their right to beconsidered as separate species. They should, we are told,be considered as mere colour phases. To this, however,. Plate 74. JACKDAW—Corviis moiiedula. Length, 14 in. ; wing, 9-3 in. [Passeres : Corvidce.]2 D 236 BRITAINS BIRDS AND THEIR NESTS. 237 there is one important objection. When interbreedingoccurs, obvious hybrids are sometimes produced; but itseems to be more usual for half the brood to turn outBlack and half Hooded. This implies a considerableamount of fixity of the characteristics in question, andplaces the divergences on a different level from ordinarycolour phases,* where such an endless series of intermediateforms exists that it is difficult to find two individuals alike,and impossible definitely to lay down any hard-and-fasttypes. The fixity of the difference seems to make thebirds more than colour phases; but still the degree ofdifference may be so slight as to make them somethingless 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 wecan
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