Except for the immature individual from 5 km. WSW Puerto Juarez, all specimens were taken in mist nets over the cenote at Pisté where Petrochelidon fulva also was obtained.
Specimens (7): ♂, 40694, imm., 16.2 gm., ♀, 40691, ovary inactive, 16.4 gm., molting—general body molt, 5th primaries and middle pair of rectrices ensheathed, ♀, 40712, imm., 14.5 gm., ♀, 40706, 14.8 gm., ♂, 40715, 16.4 gm., ♂, 40710, 18.5 gm., molting—general body molt, 1st primaries and middle pair of rectrices ensheathed, all from Pisté, July 21 and 25; ♂, 40720, imm., 15.5 gm. (August 1), 5 km. WSW Puerto Juarez.
Hirundo rustica erythrogaster Boddaert: Barn Swallow.—Specimen (1): ♀, 40721, imm., 7.3 gm. (August 18), apparently an early migrant, 2 km. WSW Sisal.
Iridoprocne albilinea (Lawrence): Mangrove Swallow.—Specimen (1): ♀, 40722, imm. (July 7), Puerto Real, Isla del Carmen.
Cissilopha yucatanica (Dubois): Yucatán Jay.—Heretofore, breeding activity has been recorded only in March (Paynter, 1955a:217). All specimens in my collection have extensively worn plumage and were beginning to molt.
Specimens (6): ♂, 40726, left testis 9 × 7 mm., right testis 4 × 2 mm., brood patch, 122.3 gm., molting—1st and 2nd primaries ensheathed (July 10), 5 km. S Champotón; ♂, 40727, testis 5 × 3 mm., brood patch, 125.6 gm., molting—1st and 2nd primaries ensheathed (July 11), 5 km. SW Champotón; ♀, 40728, 109.8 gm. (July 13), and sex? 40729, 109.5 gm. (July 15), 7½ km. W Escárcega; ♀, 40730, imm., 110.3 gm. (July 21), Pisté; ♀, 40731, ovary inactive, brood patch refeathering, 121 gm., molting—2nd and 3rd primaries ensheathed (August 16), 4 km. NNE Felipe Carrillo Puerto.
Cyanocorax yncas maya (van Rossem): Green Jay.—There are records of breeding by this species on the peninsula for April 28 and 29, and June 4 (Paynter, 1955a:215, 216).
Specimens (4): ♂, 40740, testis 5 × 3 mm., 81.2 gm. (July 16), 7½ km. W Escárcega; ♀, 40739, juv., 62.3 gm. (July 21), ♂, 40737, 64.5 gm. (July 21), and ♀, 40738, 64.1 gm. (July 21), Pisté.
Psilorhinus morio (Wagler): Brown Jay.—Specimens (3): ♀, 40742, 203.5 gm. (July 13), ♂, 40743, juv., 170 gm. (July 14), 7½ km. W Escárcega; ♂, 40741, juv., 193.7 gm. (August 14), 4 km. NNE Felipe Carrillo Puerto.
Thryothorus lucovicianus albinucha (Cabot): Carolina Wren.—This wren formerly was considered to be a species (T. albinucha). In the light of evidence presented by Lowery and Berrett (1963), it is advisable to follow Paynter (1955a:219) and consider albinucha to be a subspecies of T. ludovicianus. The only previous evidence of breeding by this species on the peninsula was a male having slightly enlarged gonads taken by Paynter (1955a:219) on March 9.