M. Fabcr on the Breeding Spots of Birds. 23' 



of these species which I have examined at the breeding season, 

 I have not seen a single instance of these being wanting, or of 

 their varying in position and number in the individuals of the 

 same species. For they are not a consequence of an unusual 

 deficiency of feathers in these birds, but they follow the most 

 precise rules both in regard to position and number, and furnish 

 a sure specific character of the different boreal aquatic birds. 



Their number is only two ; in my prodromus (p. 90.) it is 

 indeed stated that the Larus tridactyhiS has from three to four. 

 But I had before me at the time specimens which were only com- 

 mencing the process of the removal of feathers from the belly ; 

 and I do not doubt, but that, as in the other northern gulls, 

 these different patches would have united into a single one in the 

 centre of the abdomen, when it had assumed its finished form. 

 The Phalaropus, Uria grille and alle, Alca torda, Mormon 

 fratercula^ Lcstris, have two breeding spots. The Uria brun- 

 nichii and troUe, Pujfinus arcticus^ Sterna arciica, Larus tri- 

 dacti/lits, glattctts, marinus, and the Procellaria gUicialis, have 

 but one spot. One of the most important distinctions between 

 the Alca torda. and Uria troile auctorum is, that the former has 

 two and the latter but one breeding spot. 



In regard to position, they are always on the belly, never on 

 the breast ; and when one only is present, it is constantly in the 

 middle of the belly ; when two exist, they are symmetrically on 

 each side. Their Jbrm is circular and proportioned to the size 

 and number of the eggs which they have to cover. A central 

 spot is always larger than each of a pair. 



Their number occasionally corresponds to that of i;he eggs, 

 but sometimes there are more eggs than spots, as in the Larus ; 

 in the Alca torda, and Mormon f rater cula, the spots exceed the 

 eggs in number. When a bird has more eggs than spots, these 

 are generally large, and capable of including more than a single 

 ^gg* When the spots are more numerous than the eggs, these 

 change their position. 



from the deficiency of the breeding-spots in the PhalaropiUy a similar defect 

 in the breeding impulse ? This genus would then be a solitary exception, 

 of one individual laying the eggs, and another hatching them. It must, how- 

 ever, be observed in general, that we can always infer the breeding impulse 

 to be present when breeding-spots exist, but not vice verta ; as, for example, 

 neither sex of the Snla or Carbo has breeding spots, although both hatch. 



