614 STERCORAEIUS PARASITICUS, PARASITIC JAEGER. 



to \\bite ; so that the bird tends at once to assume the bicolor plumage of the adults 

 wirhdut jjoiug thiou'-h the dusky-unicolor sta^fe. This is one of the perplexing facts 

 we euconutcr iu studying the question. We liud that the very immature plumage of 

 the young birds in August can be traced through one series directly into the Insco- 

 Tinicolor stage ; through another into a state which seems to pass directly into that of 

 the normally-colored, fully adult bird. Various explanations have been offered to ac- 

 count for the dusky stage of plumage. Some authors consider it as a sexual feature, 

 regarding it as the normal adult plumage of one sex (according to some the male ; to> 

 others the female!) Others look upon it as a seasonal feature, attained at a certaiu 

 time iu each year, and regularly recurring each successive season. Still others, again, 

 consider it as a distinct variety, accidental and irregular according to some, permanent 

 according to others. With regard to the question of the sexual nature of this state, I 

 think the evidence is decidedly against such a belief. The very fact that those authors 

 who contend for this opinion difier as to which sex — some affirming that they found 

 testicles and others that they saw ovaries in the dusky birds they dissected — seems to 

 me conclusive evidence that the state of plumago in question is common to both sexes. 

 I cannot admit the hypothesis that this state constitutes a permanent or accidental 

 variety. I do not think it possible that normally-colored adult birds can have young 

 which attain at once this dusky state and retain it during their lives; still less that 

 they can transmit their abnormal characters to their offspring, as would be neces- 

 sary to constitute a permanent variety. The supposition that it is a purely accidental 

 variety — i. e., that certain individuals, without any cause, by a freak of nature as it 

 were, become thus colored and remain so for their whole lives — seems still less worthy 

 of credence. Examples of this condition of plumage are tbo numerous, and bear alto- 

 gether too definite relations with certain other stages, not to be brought about by and 

 dependent upon some definite law. The preceding suppositions being untenable, I 

 think there can be no reasonable doubt as to the true character of the stage of plum- 

 age in question, from the amount of evidence which we have tending to prove it de- 

 I)endent upon age and season. I do not hesitate, therefore, to express the decided 

 opinion that this imicolor state is a transient, immature stage of plumage, i)erfectly 

 normal, and universal, or nearly so, independently of sex, which every Jiiger — or at 

 least the great majority of individuals — passes through iu its progress toward ma- 

 turity, after leaving the plumage it first assumed, and before it arrives at the plumage 

 which is indicative of maturity. The only question is, exactly what age this plumage 

 is indicative of, and whether, after once having attained to this fully mature condilrion, 

 the adults do or do not return to this uuicolor state at certain season of each year. 

 My opinion is, that it supervenes, ordinarily at least, directly upon the disappearance of 

 the rufous, which is characteristic of the very young bird, and therefore is probably as- 

 sumed after the first moult and retained until the second. I do not think it proiable 

 that the adults which have passed through this state ever return to it ; for, as remarked 

 under head of S. jmmatorhinns, we nearly always find these uuicolor birds possessed of 

 of smaller, weaker bills, and slenderer, generally particolored, feet; all of which char- 

 acters are invariably indicative of the immature bird. 



Synoinj^nij. — It is difficult, perhaps impossible, to say whether the names and descrip- 

 tions of authors before 1800 really refer to this species or to the hnffoni. It is most 

 probable, however, that the former is really the species meant, both because it is the 

 most abundant and well known, and because Eetzius, in his edition of the Fn. Suec. 

 (in which work the species is definitely settled by giving the exact length of the cen- 

 tral rectrices*), cites as synonymous nearly all the names and descriptions in question. 

 He errs, however, in adducing S. longicaudatus, Brisson, which is the huffoni. Catha- 

 racta parasitica of Briinnich and the Larus parasiticus of Linujeus, Gmelin, and Latham 

 in all probability really refer to this species, and it is from the former of these authors 

 that the specific name is accepted. But Larus parasiticus of Latham (1790) may have 

 been based upon the long tailed species, for the reason that the length of his bird is 

 given as 21 inches — a dimension never attained by parasiticus. The synonyms of the 

 two species are indiscriminately cited. 



The Catharacta coprotheres of Briiunich is this species in its fusco-nnicolor stage. On 

 its very first introduction, in 1764, Briinnich himself doubts its validity as a species, 

 and says of it: "An precedenti — parasiticus — sexu vel specie divej'sa" ? Yet down to the 

 present time it has always been held by some authors as distinct. Thus, in 1856, Bona- 

 ]>arte gives a variety {coprotheres), and still later, in 1860, Des Murs presents a species 

 ( Lestris coprotheres). 



An early, detailed, and unmistakable description of this species is that of Brisson, in 

 1760, who gives an accurate account of it under the mononomial appellation sterco- 

 rarius. The species serves as the type of his genus. 



The Strrcorarius crejndatus of Vieillot (ut supra) is based upon this species, although 

 his specific name is taken from Gmelin and Latham, who probably based their de- 

 scriptions of crepidatus upon the young poinatorhinus. So, also, the Lestris crepidata of 



* Fu. Suec. p. 180 : " Rectrices 6, 6 (i. e., the central pair) ca>teris 4 poll, longiores." 



