seems to be generally conceded, however, that Professor Baird was right
in this determination ; therefore, as Dr. Coues surmises (Pr. Ac. Nat. Sci.
Phila. 1872, p. 68), Tyrannula mexicana, Kaup, and T. cooperi, Kaup,
must have been based upon variations of one species — the one under con-
sideration !
In attempting to determine to which of the two forms of the species Dr. MerrilPs specimens belonged, I found it necessary to carefully examine all the material available. This consisted of twenty-four specimens, belong- ing chiefly to the collection of the National Museum. After taking care- ful measurements of every specimen, and submitting all to the closest scrutiny and comparison, I found myself forced to a conclusion different from that reached by Dr. Coues (see Bull. U. S. Geol. and Geog. Surv. Terr. IV, No. 1, pp. 32, 33), in whose opinion regarding the matter I had previously coincided. I now find, that (1) while extreme examples of var. cooperi are astonishingly different from erythrocercus proper, such individuals form a very small proportion of the whole, and are chiefly from Western and Southwestern Mexico, where several other species of birds, notably Pyranga cestiva (var. cooperi, Ridgw.), attain the same great development of the bill (and, in fact, all the measurements); that (2) nearly all specimens from Mexico and Guatemala should be referred to cooperi, examples referable to erythrocercus on account of dimensions and shades of color being comparatively rare. Besides averaging larger than var. erythrocercus, var. cooperi has usually a grayer cast of plum- age, in this respect corresponding to the Mexican race of Tyrannus melancholicus (var. couchi, Baird), Hyiarchus lawrencii, and numerous other birds of similar geographical distribution. The only satisfac- tory test, however, which I have been able to apply in determining to which race doubtful specimens should be referred is that of size, as follows : —
Yar. erythrocercus. — Wing, 3.40-3.95 (average, 3.77) ; tail, 3.60- 4.00 (average, 3.82); bill, from nostril, .55-68 (average, .61); tarsus, .85-.88 (average, .86)* Hab. — Eastern Tropical America, from Para- guay to Southern Mexico, but chiefly southward of the latter country. Yar. cooperi. — Wing, 3.85-4.45 (average, 4.15) ; tail, 4.00-4.60 (aver- age, 4.25); bill, from nostril, .60-.82 (average, .69); tarsus, .88-.95 (av- Six specimens, as follows^ —
 | A table should appear at this position in the text. See Help:Table for formatting instructions. |
ti- cs p _* £ 3 fl s O a oo OQ 3 W 3 ? ad. % 16348 U.S. 16349 -ad. U.S. •29423 -ad. U.S. 39210 d ad. U.S. 39213 — ad. U.S. 57649 cf ad. U.S. Locality. Date. ! .2 "Brazil" Paraguay Costa Rica Merida. Yucatan do Sta. Efigenia, Tehuantepec . , Aug. — , 1859 May — , 1859 May 29,1865 Apr. 9, 1865 Dec. 18, 1868 3.65 3.75 3.90 3.95 3. 40 3.95 C3 H ft H 3.60 .58 .85 3.80 .60 .85 3. SO .62 .88 3 95 .68 .85 3. 75 4.00 .55 I .88
