_Thalasseus sandvicensis_ (Latham): Cabot Tern.--Lone individuals were seen several times flying along the coast southwest of Sisal. Specimen (1): [Male], 40452, 186 gm. (August 11), 13 km. WSW Sisal. Mallophaga: _Saemundssonia brevicernis_. _Patagioenas flavirostris flavirostris_ (Wagler): Red-billed Pigeon.--This species was seen at all stations except on the islands and in the arid scrub at Sisal. It was especially abundant at Escárcega, Felipe Carrillo Puerto, and Puerto Juarez. The male in breeding condition suggests that the breeding season extends into the summer. Specimens (5): [Female], 40455, ovary inactive (July 13), [Female], 40456, ovary inactive, (July 13), and [Male], 40457, testis 7 × 5 mm. (July 15), 6-{7-1/2} km. W Escárcega; [Male], 40453, testis 15 × 6 mm., 225.5 gm. (August 16), and [Female], 40454, ovary inactive, 228 gm. (August 16), 4 km. NNE Felipe Carrillo Puerto. Mallophaga: _Columbicola_ sp., July 15. _Zenaida aurita yucatanensis_ Salvadori: Zenaida Dove.--This species was common at Sisal. Specimens (3): [Female], 40459, imm., 136.5 gm., little fat (August 11), 8 km. SW Sisal; [Female], 40399, 151.2 gm. (August 7), 1-1/2 mi. S Sisal; [Female], 40400, 163.3 gm. (August 18), 2 km. WSW Sisal. Mallophaga: _Columbicola macrouras_, August 7. _Zenaida asiatica_ Linnaeus: White-winged Dove.--Birds of this species were ubiquitous in the scrub west of Sisal between 10 a.m. and 4 p.m. but inconspicuous at other times. Apparently the birds were from nests, roosts, and watering sites in the taller forest inland. _Columbina passerina pallescens_ (Baird): Common Ground Dove.--This species was common at almost all collecting localities, but was always outnumbered by the Ruddy Ground Dove. The species was not seen in the vicinity of Escárcega, probably because of the tall forest and lack of clearings there. Specimens (5): [Male], 40461, testis 10 × 5 mm., 40.9 gm. (August 10), 2 km. WSW Sisal; [Male], 40460, testis 6 × 3 mm. (August 9), and [Female], 40464, ova to 4 mm., 37 gm. (August 9), {3-1/2}-4 km. N San Miguel, Isla Cozumel; [Female], 40463, imm., molting, 35.5 gm. (August 15), 4 km. NNE Felipe Carrillo Puerto. _Columbina talpacoti rufipennis_ (Bonaparte): Ruddy Ground Dove.--This dove was common at all localities visited. All specimens were in breeding condition.