12 THE NESTS AND EGGS OF BRITISH BIRDS. 



or less uniformly distributed over the entire surface. 

 Some examples are very sparingly marked, and mostly 

 with underlying spots. In shape and size also they vary 

 considerably. Average measurement, r45 inch in length, 

 by ro inch in breadth. Incubation, performed by both 

 sexes, lasts from seventeen to eighteen days. 



Diagnostic characters : The clear blue or pale 

 green ground colour, and comparatively few and well- 

 defined markings, readily distinguish the eggs of the 

 Jackdaw from allied British species. The eggs most 

 likely to be confused with them are those of the Chough 

 and certain pale varieties of those of the Magpie, but the 

 clear definition of the surface-spots is a pretty safe guide. 

 It must also be borne in mind that the Jackdaw rarely 

 or never breeds near the colonies of the Choughs and 

 the exposed, domed nest of the Magpie in the branches 

 is ever an unfailing means of distinction. 



Family CORVID/E. Genus rvRRHOCOUAX. 



COMMON CHOUGH. 



Pyrrhocorax graculus {Liunccus). 



Single Brooded. Laying season, May. 



British breeding area : The Chough is now one 

 of the rarest and most local of our indigenous birds, and 

 though formerly fairly common in many inland districst, 

 is now almost without exception only met with during 

 the breeding season on the wildest and most inaccessible 

 ocean cliffs. Even here many of its scattered colonics 

 have been deserted, for no apparent cause, within com- 



