Page:Auk Volume 13-1896.djvu/183

Vol. XIII , A New Chordeiles from Costa Rica. 135 Two downy young taken by Mr. John Schaler from the same nest at Rock Lake, on July 17, have an interrupted black bar across the breast, black at the base of the mandible, and the entire upper parts mottled with black, but while the ground color of one is pure white, that of the other is pale ochraceous-buff, becoming white only in the center of the abdomen. This difference may be one of sex, or, taken in connection with the ochraceous females mentioned, connect sennetti with henryi.

Wherever we went about the prairies we found this bird a rather common summer resident, especially in the neighborhood of water. It arrives the last week in May, and begins laying about the twentieth of June. The pale colors of the male protect him admirably, harmonizing with the dull gray of the fences and rocks, perched on which he passes the day, while the darker colors of the female render her less conspicuous when seated over her eggs on the black soil. Six eggs in my collection from Towner County average 1.67 in. in length by .88 in. in breadth, and are perhaps a trifle paler with somewhat smaller markings than eggs of virginianus.

Average measurement (with extremes) of thirteen specimens (10 ♂, 3♀): length, 9.53 (9.25-9.81); wing, 7.61 (7.08-7.87); tail, 4.68 (4.53-4.79).

is with much hesitation that I present the following as characterizing a new Nighthawk of the C. virginiatius group,—that is, the species or subspecies in which the white wing-patch is posterior to the tips of the secondaries.