_Nyctidromus albicollis yucatanensis_ Nelson: Parauque.--This species was especially common in the vicinity of Felipe Carrillo Puerto and on Isla Cozumel, and was seen at every collecting locality. A flightless, juvenal female was obtained by local boys at Pisté on July 21. Therefore the reproduction period seems to be longer than Paynter's (1955a:141) data suggested. Specimens (5): [Male], 40512, testis 7 × 3 mm., 75 gm. (July 10), 5 km. S Champotón; [Female], 40508, juv. (remiges and rectrices ensheathed basally), 44.2 gm. (July 21), Pisté; sex? 40510, 55.5 gm. (August 8), and [Male], 40509, testis 3 × 1 mm., 73.5 gm., molting--outermost two pairs of primaries ensheathed (August 10); 3-1/2 km. N San Miguel, Isla Cozumel; [Male], 40511, 72.9 gm. (August 15), 4 km. NNE Felipe Carrillo Puerto. _Caprimulgus salvini badius_ (Bangs and Peck): Salvin's Whip-poor-will.--My only record of this species is provided by a female (40513) taken 3-1/2 km. N San Miguel, Isla Cozumel, on August 8. The specimen weighed 58 grams, had an inactive ovary (6 × 4 mm.), and was molting (8th and 9th primaries ensheathed). _Chateura vauxi gaumeri_ Lawrence: Vaux Swift.--This species was seen at almost every locality visited. The only specimens obtained were brought in by a boy at Pueblo Nuevo X-can on July 30; he said he captured them in his house. Two of them were adults and four were fully-feathered young-of-the-year. Specimens (6): [Male], 40516, testis 4 × 2 mm., [Female], 40519, ovary inactive, [Male], 40514, juv., 12.6 gm., [Male], 40515, juv., [Female], 40517, juv., and [Female], 40518, juv. (July 30) Pueblo Nuevo X-can. _Campylopterus curvipennis pampa_ (Lesson): Saber-wing.--A female (40522), shot 7-1/2, km. W Escárcega on July 16, seems to provide the first record of breeding (ovum 6 mm. in oviduct) by this species on the peninsula. A non-breeding female (40521) that weighed 5.0 gms. was taken 4 km. NNE Felipe Carrillo Puerto on August 14. _Chlorostilbon canivetii canivetii_ (Lesson): Canivet Emerald.--This bird was seen at all localities at which we collected on the mainland. Specimens (4): [Female], 40530, ovary moderately active, 3.0 gm. (July 22), [Male], 40525, 2.1 gm. (July 23), and sex? 40526, 2.9 gm. (July 25), Pisté; [Female], 40529, ovary inactive, 2.4 gm. (July 26), 3-1/2 km. N Pisté. _Chlorostilbon canivetii forificatus_ Ridgway: Canivet Emerald.--The specimen is slightly larger than those taken on the mainland and is clearly referable to _C. c. forificatus_, a subspecies endemic to Isla Cozumel. Specimen (1): [Female], 40534, ovary inactive, 2.8 gm. (August 8), 3-1/2 km. N San Miguel, Isla Cozumel. _Amazilia candida candida_ (Bourcier and Mulsant): White-bellied Emerald.--This species seemed to be the commonest hummingbird at most localities on the mainland. However, it was not seen along the coasts.