_Polioptila caerulea_ (Linnaeus): Blue-gray Gnatcatcher.--A fledgling taken at Pisté was barely flying with remiges and rectrices ensheathed basally. Previous breeding records are for April 11 and 27 (Paynter, 1955a:231). A male taken on August 10 on Isla Cozumel had nearly completed molting into winter plumage. Specimens (8): [Female], 40788, fledgling, 5.0 gm. (July 20), 6-1/2 km. W Pisté; [Male], 40787, testis 2 × 1 mm., 5.6 gm. (July 21), [Male], 40785, juv., 5.8 gm. (July 22), and [Female], 40786, 5.6 gm. (July 22), Pisté; [Female], 40791, juv., 5.6 gm. (August 8), [Male], 40790, juv., 5.8 gm. (August 8), [Female], 40789, 5.7 gm. (August 9), and [Male], 40792, 5.3 gm., molting--7th primaries ensheathed (August 10), from {2-1/2}-{3-1/2} km. N San Miguel, Isla Cozumel. _Polioptila albiloris_ Lawrence: White-lored Gnatcatcher.--This species was abundant in the arid scrub along the coast in the vicinity of Sisal. Specimens (2): [Male], 40783, testis 1 mm., 6.2 gm. (August 7), 1-1/2 mi. S Sisal; [Male], 40784, testis 1 mm., 5.8 gm. starting to molt--1st and 2nd primaries ensheathed (August 10), 13 km. WSW Sisal. _Ramphocaenus rufiventris_ (Bonaparte): Long-billed Gnatwren.--Specimen (1): [Female], 40793, imm. skull, 9.8 gm. (July 15), 7-1/2 km. W Escárcega. _Cyclarhis gujanensis insularis_ Ridgway: Rufous-browed Pepper-shrike. --Specimen (1): [Male], 40794, testis 2 mm., 37.8 gm., molting--4th primaries ensheathed (August 9), 4 km. N San Miguel, Isla Cozumel. _Vireo bairdii_ (Ridgway): Cozumel Vireo.--Specimens (4): [Female], 40795, ovary inactive, 12.7 (August 8), [Male], 40796, testis 2 mm., 12.6 gm., molting--3rd and 4th primaries ensheathed (August 10), [Female], 40797, ovary inactive, 12.5 gm., molting--3rd primaries ensheathed (August 10), and [Male], 47098, imm., 13.1 gm. (August 10), from 2-1/2-3-1/2 km. N San Miguel, Isla Cozumel. _Vireo pallens semiflavus_ (Salvin): Mangrove Vireo.--Paynter (1955a:236) noted breeding by this species from April 7 through June. Specimens (2): [Female], 40800, ova to 3 mm., oviduct enlarged (July 8), Isla del Carmen; [Female], 40799, ovary inactive, 11.1 gm., molting--4th primaries ensheathed (August 2), Isla Mujeres. _Vireo flavoviridus flavoviridus_ (Cassin): Yellow-green Vireo.--Paynter's (1955a:238) data indicate breeding in this species from late May through June; our records indicate that the species breeds at least through July.