_Stelgidopteryx ruficollis_ Audubon: Rough-winged Swallow.--Previous records indicate that three subspecies of this species occur on the Yucatán Peninsula (Paynter, 1955a:209). One of these, _S. r. ridgwayi_, is resident. _S. r. serripennis_, representing the breeding population occurring from British Columbia and New Hampshire over much of the United States to central California, central Texas, and the Gulf states, has been taken on the peninsula in winter. Paynter referred two specimens taken in late September and three January-taken specimens to _S. r. stuarti_, the highland race that breeds from the mountains of southern Veracruz to Guatamala. Allan R. Phillips had identified two immature individuals (40694 and 40712) from Pisté as _S. r. stuarti_; one specimen from Puerto Juarez also is an immature and is nearly identical to those from Pisté. Two adults from Pisté (40691 and 40710) are noticeably darker dorsally than the immatures but are molting extensively and their identification to subspecies is equivocal. Two other adults (40706 and 40715) were prepared as skeletons. Although mid-July seems early for _S. r. stuarti_ to be present on the peninsula it is not too surprising since the three specimens positively identified are immature birds and young possibly arrive earlier than do adults. But, the immature specimens possibly are atypical individuals of the resident population of _S. r. ridgwayi_. 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): [Male], 40694, imm., 16.2 gm., [Female], 40691, ovary inactive, 16.4 gm., molting--general body molt, 5th primaries and middle pair of rectrices ensheathed, [Female], 40712, imm., 14.5 gm., [Female], 40706, 14.8 gm., [Male], 40715, 16.4 gm., [Male], 40710, 18.5 gm., molting--general body molt, 1st primaries and middle pair of rectrices ensheathed, all from Pisté, July 21 and 25; [Male], 40720, imm., 15.5 gm. (August 1), 5 km. WSW Puerto Juarez. _Hirundo rustica erythrogaster_ Boddaert: Barn Swallow.--Specimen (1): [Female], 40721, imm., 7.3 gm. (August 18), apparently an early migrant, 2 km. WSW Sisal. _Iridoprocne albilinea_ (Lawrence): Mangrove Swallow.--Specimen (1): [Female], 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.