_Campylorhynchus yucatanicus_ (Hellmayr): Yucatán Wren.--This species was abundant in the coastal scrub west of Sisal where some breeding activity was noted. A few individuals were carrying nest material and several were feeding young. There were many old and abandoned nests and apparently the breeding season was nearly over. The only previous breeding record is for March 19 when a newly completed nest was found (Paynter, 1955a:218). Specimens (4): [Male], 40750, imm., 32.4 gm. (August 7), 1-1/2 mi. SW Sisal; [Female], 40751, imm., 31.2 gm. (August 18), 2 km. WSW Sisal; [Female], 40752, ovary 7 × 3 mm., 40 gm. (August 9), 4.3 km. WSW Sisal; [Female], 40753, 31.0 gm. (August 11), 6-1/2 km. WSW Sisal. _Melanoptila glabrirostris cozumelana_ (Paynter): Black Catbird.-- Apparently the only previous record of breeding by this species was Paynter's (1955b) mention of a male from Quintana Roo with enlarged gonads on June 26. The three adults in the collection here reported on were in nearly full reproductive activity. Specimens (4): [Male], 40764, imm., 40.5 gm. (August 8), [Female], 40767, testis 8 × 4 mm., 42.0 gm., heavy fat (August 8), [Female], 40765, ovary active (oviduct enlarged), brood patch, 35.2 gm. (August 10), and [Male], 40766, testis 9 × 6 mm., 35 gm. (August 10), from 2-1/2-3-1/2 km. N San Miguel, Isla Cozumel. _Mimus gilvus_ (Vieillot): Tropical Mockingbird.--The only breeding record heretofore is by Paynter (1955a:226) of newly-fledged juveniles taken on May 26 and 29. Gonads in our adults were moderately active; feathers were extremely worn, but molting was not evident. Specimens (4): [Male], 40771, testis 9 × 6 mm., 51.0 gm. (July 9), 5 km. S Champotón; [Female], 40770, ovary moderately active (ova to 2 mm.), brood patch, 42 gm., moderate fat (August 9), 3-1/2 km. N San Miguel, Isla Cozumel; [Female], 40768, imm., 45.2 gm., moderate fat (August 18), 2 km. WSW Sisal; [Male], 40769, testis 10 × 5 mm., 51.8 gm. (August 9), 13 km. WSW Sisal. Mallophaga: _Myrsidea_ sp., July 9. _Toxostoma guttatum_ (Ridgway): Cozumel Thrasher.--Our specimen had enlarged testes and seems to represent the first record of breeding activity in the species. Specimen (1): [Male], 40772, testis 7 × 4 mm., 49.5 gm. (August 10), 3-1/2 km. N San Miguel, Isla Cozumel. _Turdus grayi_ Bonaparte: Clay-colored Robin.--Four adults were in full breeding condition. Specimens (6): [Male], 40780, testis 13 × 8 mm., brood patch (July 10), 5 km. S Champotón; [Female], 40781, ova to 8 mm., 79.6 gm. (July 15), 5 km. SW Escárcega; [Female], 40776, 61.3 gm. (July 21), Pisté; [Female], 40777, imm., 63.4 gm. (July 20), 6½ km. W Pisté; [Male], 40779, testis 14 × 8 mm., brood patch, 68.5 gm. (July 30), and [Male], 40778, testis 13 × 11 mm., 71.5 gm. (July 28), Pueblo Nuevo X-can.