A REVISION OF THE AMERICAN GREAT HORNED OWLS. 



By Harry C OiiERHOLSEK, 



Assi.'itaiil OrnithohKjiM, Departuie.nt of Agriculture. 



The difficulty of aceuinulatino- a satisfactory amount of material has 

 always been a serious obstacle in the stud}- of the great horned owls. 

 The author has been fortunate enough to bring together more than 2< H) 

 specimens, representing all but one of the American forms, and the 

 opportunity- thus afforded for a better luiderstanding of their relation- 

 ships has, of course, been exceptional. 



Tliat the numl)er of subspecies must be considerably incnnised is 

 hardly surprising, in view of the comparatively small numl)er hitherto 

 recognized and the great geographical area involved. It is evident, 

 however, that there is but one species in all America — North. (\^ntral, 

 and South, the various races being iutimatel}- connected by individual 

 or geographical intergrades. In contrast to the condition existing in 

 many other similarly plastic types, very few of the New World n^pre- 

 sentatives of Aslo" are contined within close!}' circumscribed geograph- 

 ical limits. With the exception of occidental is and irapdcuilni. all 

 seem to l)e strictly nonmigratory. and thus any record safely may be 

 considered as based upon the resident bird. 



Although size seems to be the sole sexual difference, the range of 

 indixidual variation is very great, further complicating the ah'eady 

 ditlicult problem of relationship. A kev to the solution of this prob- 

 lem is furnished b}' what is probably the most interesting result of 

 the present study — the discovery of the fact that there exists in at 

 least several of the American forms, and probably in not a few of the 

 Old World species as well, a dichromatism, comparable to that of the 

 genus ^>/'^/.s/^ though ])erliaps not so impivssive, which is manifested 

 in a light and a dark, sometimes also a rufous or ochraceous. phase, 

 independent of sex, age, season, or locality; in extreme conditions 

 entirely distinct, yet completely connected by various intermediates. 



"The proper name of Bnlio. For explanation of the change see Stone, Auk, XX, 

 1!H)3, pp. 272-278. 



''An earher name U>r Phorhhm {=Mc(j(tscoi)x). See Stone, Auk, XX, U>0:i, pp. 

 272-276. 



Proceedings U. S. National Museum, Vol. XXVII— No. 1352. 



17' 



