FALCONIDAE. 



A few additional specific characteristics. 



CIRCUS CYANEUS (L.). 



Proportionately more spotted eggs are found among those of 

 cyaneus than among those of the other species. 



Von RiESENTHAL observed that in some years spotted eggs occur 

 more numerously than in other years. 



Red and rusty-red spots, which Rey mentions, are in my opinion 

 frequently caused by nest-materials, as is also the case, e. g. with 

 eggs of the Colymbidae. (See also below at aeruginosas). The 

 spotted eggs, shown in Dresser's ') Work under 4 and 6 on plate 

 I (part 1, page 7) remind one of sparsely spotted eggs of Accipiter 

 nisus. 



CIRCUS PYGARGUS (L.). 



These eggs, whose shape often reminds one of eggs of Strigidae, 

 are as a rule smaller than those of cyaneus and are spotted much 

 more rarely. Von Riesenthal had never seen spotted eggs; if mar- 

 kings occur these, Rey says, are much fainter than in the case 

 of cyaneus. 



CIRCUS AERUGINOSUS (L.). 



Layer II of these eggs is usually so thick that the oocyanin of 

 layer I only rarely gives any tint to the surface of the shell; occa- 

 sionally this surface exhibits a few accessory spots caused by 

 nest-dirt. 



Neither Altum, Von Riesenthal, nor Rey make mention of real 

 pigment markings. Yet these seem to occur occasionally; but in 

 order to show how rarely they occur, I quote what Mr. W. Schluter, 



') Eggs of the Birds of Europe. London, 1905— '10. 



