Specimens (3): [Male], 40441, testis 3 mm., 242.3 gm., wing 205 mm., tail 80 mm., tarsus 66 mm., culmen (from feathers) 60 mm.

(August 9), [Female], 40440, ovary inactive, 240.5 gm., wing 204 mm., tail 77 mm., tarsus 69 mm., culmen (from feathers) 59 mm.

(August 11), and [Male], 40442, imm., 221.1 gm. (August 11) 8-13 km. WSW Sisal. Mallophaga: _Austrominopon sachlebeni_, August 9; _Quadraceps carrikeri_, August 11.

_Arenaria interpres_ (Linnaeus): Turnstone.--Six individuals were sighted on Isla Mujeres on August 1 and one individual was sighted 4 km. W Sisal on August 11.

_Crocethia alba_ (Pallas): Sanderling.--This species was relatively common at Sisal where several flocks of 30 to 40 birds were seen. One specimen (40444) shows an unusual pattern of molt; replacement of outer primaries has preceded that of the inner.

Specimens (4): [Male], 40445, testis 3 1 mm., 57.5 gm., heavy fat (August 9), [Female], 40444, ovary granular 6 3 mm., 56.7 gm., molting (August 11), [Male], 40443, 35.5 gm. (August 11), and [Female], 40446, imm., 54.1 gm. (August 11), 6-1/2-13 km. WSW Sisal. Mallophaga: _Lunaceps holophaeus actophilus_, August 11; _Carduiceps zonarius_, August 11.

_Ereunetes pusillus_ (Linnaeus): Semipalmated Sandpiper.--The only individual seen was taken from a mixed flock of Sanderlings and Wilson Plovers.

Specimen (1): [Male], 40447, testis minute, 24.4 gm. (August 11), 8 km. WSW Sisal.

_Himantopus mexica.n.u.s_ (Muller): Black-necked Stilt.--A lone individual was sighted on Isla Mujeres on August 2. A pair was on the mudflats among mangroves at Sisal, of which the male was taken on August 7.

Although Paynter (1955a) indicated that this species probably breeds on the peninsula, there are no definite breeding records. Our specimen had only slightly enlarged testes, but its close a.s.sociation with a female suggested that the pair may have been mated.

Specimen (1): [Male], 40448, testis 7 3 mm., 189.4 gm., little fat (August 7), 5 mi. SW Sisal.

_Larus atricilla_ Linnaeus: Laughing Gull.--This species was seen regularly along the coasts of the peninsula.

Specimen (1): [Female], 40449, ovary 7 mm. (inactive), 253 gm.

(August 7), 4-3/10 mi. W Sisal. Mallophaga: _Quadraceps_ sp.

_Sterna albifrons antillarum_ (Lesson): Least Tern.--A flock of about 20 individuals was seen on Isla Mujeres; two individuals were shot and appear to be the first specimens from the island.

Specimens (2): [Female], 40451, ovary slightly enlarged, 49.0 gm.

(August 2); s.e.x? 40450, 41.8 gm. (August 2), Isla Mujeres.

_Thala.s.seus 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 Escarcega, 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 Escarcega; [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 pa.s.serina 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 Escarcega, 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.

Specimens (9): [Female], 40472, ova to 3 mm., 45.4 gm. (July 8), [Male], 40468, testis 10 5 mm., 50.0 gm (July 8), [Male], 40469, testis 10 5 mm., 65.5 gm. (July 8), [Female], 40470, ova to 3 mm., 51.6 gm. (July 8) and [Male], 40471, testis 9 5 mm., 57.5 gm. (July 8), all from the vicinity of Puerto Real Isla del Carmen; [Female], 40467, 57.7 gm., (July 10), 5 km. S Chapoton; [Male], 40473, testis 8 5 mm., 53.0 gm. (July 17), 1 km. N, 13 km. W Escarcega; [Female], 40465, ova to 21 mm., 51.8 gm. (July 28); Pueblo Nuevo X-can; [Male], 40466, testis 8 4 mm., 46.6 gm.

(August 16), 4 km. NNE Felipe Carrillo Puerto.

_Claravis pretiosa_ (Ferrari-Perez): Blue Ground Dove.--This species was seen only at Pueblo Nuevo X-can where a breeding pair was taken on July 29; this record extends the known breeding season by one month (see Paynter, 1955b).

Specimens (2): [Male], 40475, testis 10 5 mm., 65.0 gm. (July 29), and [Female], 40474, ova to 9 mm., 68.3 gm. (July 29), Pueblo Nuevo X-can.

_Leptotila verreauxi fulviventris_ Lawrence: White-fronted Dove.--My only records of this species are the two specimens listed below. Both birds had slightly enlarged ovaries and the one from west of Escarcega was molting. Paynter (1955a) recorded breeding from late January to late April.

Specimens (2): [Female], 40476, ova to 2 mm., molting--5th and 6th primaries ensheathed (July 14), 7-1/2 km. W Escarcega; [Female], 40477, ovary 12 5 mm., 162 gm. (August 14), 4 km. NNE Felipe Carrillo Puerto.

_Leptotila jamaicencis gaumeri_ (Lawrence): Caribbean Dove.--Two were collected on Isla Cozumel and the several white-fronted doves seen on Isla Mujeres probably were of this species.

Specimens (2): [Male], 40478, testis 9 5 mm., 175 gm., molting--4th primaries ensheathed (August 9), and [Female], 40479, imm., 116.7 gm., molting--2nd primaries ensheathed (August 10), 3-1/2 km. N San Miguel.

_Oreopeleia montana montana_ (Linnaeus): Ruddy Quail-dove.--My only record is of a male, in full breeding condition, which extends the known breeding period almost two months.

Specimen (1): [Male], 40480, testis 19 8 mm., 144.7 gm. (July 29), Pueblo Nuevo X-can.

_Artinga astec astec_ (Souance): Aztec Parakeet.--This species was most common in deciduous forest and scrub at Champoton, Piste, Puerto Juarez, and especially Felipe Carrillo Puerto. Parakeets were extremely wary and only two were collected.

Specimens (2): [Male], 40481, testis 3 2 mm., 75.0 gm., molting--extensive body molt, 8th primaries ensheathed, middle pair of rectrices are new (August 16), and [Female], 40482, ovary inactive, 72.4 gm. (August 16), 4 km. NNE Felipe Carrillo Puerto.

_Amazona xantholora_ (Gray): Yellow-lored Parrot.--The species was abundant in the vicinity of Champoton. Large flocks congregated near camp; the birds began to a.s.semble about an hour before dark. One was shot from a flock that flew over our camp and another was taken at night from its roost in a small tree about 10 feet above a trail. One small flock of _Amazona_ was seen 4 km. NNE Felipe Carrillo Puerto. All specimens were molting.

Specimens (3): [Male], 40483, testis 5 2 mm., 229.1 gm., molting--extensive body molt, 6th primaries ensheathed (July 9), and [Female], 40484, ovary 13 9 mm. (inactive), 209.0 gm., molting--extensive body molt, wing molt complete (July 11), 5 km. S Champoton; [Male], 40485, testis 5 2 mm., 210.9 gm., molting--extensive body molt, 7th primaries ensheathed (August 16), 4 km. NNE Felipe Carrillo Puerto.

_Amazona albifrons nana_ Miller: White-fronted Parrot.--This species was common west of Escarcega where large flocks were seen every evening. A specimen of _A. albifrons_ was taken south of Champoton where this species occurred in large flocks with _A. xantholora_. One specimen was taken from a small flock near Chichen-Itza.

Specimens (5): [Male], 40487, testis 8 4 mm., 210.0 gm. (July 10), 5 km. S. Champoton; [Female], 40488, ovary inactive, 205.5 gm., molting (July 12), [Male], 40489, 232.5 gm., molting (July 13), and [Female], 40490, ovary inactive, 206.1 gm. (July 14), 7-1/2 km. W Escarcega; [Female], 40486, ovary inactive, 176.0 gm.

(July 27), 2 km. E Chichen-Itza.

_Coccyzus america.n.u.s america.n.u.s_ (Linnaeus): Yellow-billed Cuckoo.--A female taken at Piste substantiates Paynter's (1955a) suggestion that the species breeds on the peninsula.

Specimen (1): [Female], 40491, ovary 12 9 mm., 58.7 gm., well-developed brood patch (July 22), Piste.

_Coccyzus minor_ (Gmelin): Mangrove Cuckoo.--In view of the paucity of recent records of this species from the mainland of the peninsula, it is noteworthy that several individuals were seen flying to and from the beach and mangroves late one evening about 4 km. W Sisal.

_Piaya cayana thermophila_ Sclater: Squirrel Cuckoo.--This species was seen at our camps near Champoton, Piste, Pueblo Nuevo X-can, and Puerto Juarez. The slightly enlarged (probably regressing) testes of males examined seem to be the only evidence of breeding activity in the species on the peninsula.

Specimens (3): [Male], 40493, testis 8 6 mm., 99.6 gm. (July 14), and [Female], 40494, 90.0 gm. (July 14), 7-1/2 km. W Escarcega; [Male], 40492, testis 5 2 mm., 97.5 gm., molting (August 14), 4 km. NNE Felipe Carrillo Puerto.

_Crotophaga sulcirostris sulcirostris_ Swainson: Grove-billed Ani.--Three half-grown juveniles were taken at Piste and a pair in breeding condition was taken at Pueblo Nuevo X-can. These seem to be the first breeding records from the peninsula.

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), Piste; [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.