Specimens (5): [Male], 40495, juv., 39.9 gm. (July 21), [Male], 40496, juv., 39.5 gm. (July 21), and [Female], 40497, juv., 30.0 gm. (July 21), Pisté; [Male], 40498, testis 11 × 4 mm., 72.2 gm. (July 28), and [Female], 40499, ova to 7 mm., 70.0 gm. (July 28), Pueblo Nuevo X-can. _Crotophaga ani_ Linnaeus: Smooth-billed Ani.--The female taken on Isla Cozumel had a slightly enlarged ovary and had been banded (USFWS band no. 524-96303) on the island in 1961 as an adult. Specimen (1): [Female], 40500, ovary 11 × 7 mm., 86 gm., molting (August 4), 3-1/2 km. N San Miguel. _Glaucidium brasilianum ridgwayi_ Sharpe: Streaked Pygmy Owl.--A female (40501) was taken by a local boy at Pueblo Nuevo X-can on July 29 weighed 62 gm. and the ovary (7 × 3 mm.) was inactive. _Ciccaba virgata centralis_ Griscom: Squamulated Owl.--Our only specimen, a female (40502) weighing 288.7 gm. and having an inactive ovary (13 × 4 mm.), was taken at night on July 16 from a mist net stretched across a small trail 1 km. N, 13 km. W Escárcega. _Nyctibius griseus mexicanus_ Nelson: Mexican Potoo.--One specimen was taken at night 7-1/2 km. W Escárcega where it was found sitting on the limb of a large dead tree. A light but steady rain was falling at the time. On the night of August 16 along a stretch of newly-constructed road 4-16 km. NNE Felipe Carrillo Puerto, 27 potoos were seen, their large and brilliant, amber-colored eyes first appearing in the headlights several hundred yards ahead of our vehicle. All of the birds were perched between 30 and 60 feet above the ground on dead limbs of large trees, and all were perched on the same side of the road facing the light of a full moon. None was less than 200 meters from the next; few flew at the approach of our vehicle. In addition to one specimen taken along the road, another was taken from a fence post in a _milpa_ on the same night. It was approached close enough to be shot with a 22 caliber pistol loaded with dust-shot. All specimens had thick layers of subcutaneous and visceral fat and their gonads were small and seemingly inactive. Specimens (3): sex? 40505 (July 13) 7-1/2 km. W Escárcega; [Female], 40504, ovary 13 × 4 mm. (inactive), 265 gm. (August 16), and [Male], 40503, testis 5 × 3 mm., 320.5 gm. (August 16) 4 km. NNE Felipe Carrillo Puerto. _Chordeiles acutipennis micromeris_ Oberholser: Trilling Nighthawk.--This species was common in the arid coastal scrub west of Sisal, where hundreds could be seen flying every evening. They were common also at Puerto Juarez, but uncommon at Felipe Carrillo Puerto. Specimens (2): [Male], 40506, testis 5 × 3 mm., 57.3 gm. (August 1), 5 km. WSW Puerto Juarez; [Female], 40507, ovary 4 × 3 mm. (inactive), 37.0 gm. (August 16), km. NNE Felipe Carrillo Puerto.