Crocethia alba (Pallas): Sanderling.—This sandpiper was noted each day along the beach, occasionally singly but more frequently in groups ranging from 10 to 50 individuals. Specimens (7): ♂, 38936, testis 2 mm., light fat, 49 gm., 5 P old, Camp 1, July 7. Female, 38937, ova to 1 mm., fat, 58 gm., 4 P old; ♂, 38939, fat, no weight recorded, 6 P old, breeding plumage; 3 ♂ ♂, 38940-38942, fat, no weight recorded, 4-5 P old; Camp 2, July 9.
With one exception as noted, our specimens are in worn, nonbreeding plumage and are replacing their old feathers with new ones fundamentally the same in color and pattern; the exceptional specimen is molting from worn breeding plumage into nonbreeding plumage. Only one other individual in breeding feather was seen on the island.
According to the Mexican Check-list (1950:99), the Sanderling has been recorded in México from August to May 19. In Texas, Peterson (1960:107) reports that it is a migrant, April to June and July to November, and that it winters along the coast. We suspect that many of the birds present in Texas in June and July, together with those recorded by us in Tamaulipas in July, are nonbreeding, summering individuals. Haverschmidt (1955:368) reports northern-summer records from Surinam, and, according to the A.O.U. Check-list (1957:208), nonbreeding birds occur in summer extensively through winter range of the species, including the Gulf coast of the United States.
Micropalama himantopus (Bonaparte): Stilt Sandpiper.—Two birds in worn winter plumage were taken as they foraged together at the edge of the laguna near Camp 2 on July 9. Specimens (2): ♂, 38934, testis 2.5 mm., heavy fat, 116 gm., 4 P old; ♂, 38935, testis 3 mm., fat, 111 gm., 4 P old.
Our specimens probably were nonbreeding birds summering between the breeding range in arctic America and the winter range in northern South America. The A.O.U. Check-list (1957:202) does not mention nonbreeding, summering records of this species. The 251 birds seen by Coffey (1960:292) at Cacalilao, Veracruz, on May 11, 1954, were probably migrants.
Recurvirostra americana Gmelin: American Avocet.—This species was seen only in three large flocks flying south along the beach, as follows: 56 birds 72 miles south of Washington Beach, July 8; 38 birds 73 miles south of Washington Beach, July 8; 29 birds 72 miles south of Washington Beach, July 10. All birds were in winter plumage.
All these birds were possibly autumnal migrants, but the dates are early; the species has not previously been recorded on migration in México before August (Mexican Check-list, 1950:101). The species is known to breed in San Luis Potosí (Mexican Check-list, loc. cit.) and along the lower coast of Texas ("rarely to Brownsville"; A.O.U. Check-list, 1957:209); avocets thus may also breed in coastal Tamaulipas.
Larus argentatus Pontoppidan: Herring Gull.—A first-year bird was observed near Camp 2 on July 8, and two subadult individuals were seen on the beach between the Third and Fourth passes on July 8.
Larus atricilla Linnaeus: Laughing Gull.—This gull was common all along the beach. Many individuals were in full breeding feather and many subadult birds were also present. Specimens (6): ♂ subadult, 38944, testis 5 × 1 mm., 325 gm., molting; ♀, 38945, ovary small, 309 gm., in molt, brood patches refeathering; sex?, 38943, 315 gm., in molt; sex? subadult, 38946, 327 gm., in molt; Camp 1, July 7. Female subadult (second-year), 38947, 305 gm., in molt, Camp 2, July 8. Female, 38926, ova to 2.5 mm., 313 gm., 8 P old, Camp 2, July 10.
The Mexican Check-list (1950:105) refers to the Laughing Gull as a common winter resident on both coasts of México from August 7 to May 17, but Loetscher (1955:29) found it locally common throughout the year on the coast of Veracruz, and he mentioned seeing birds a short distance south of Tampico in June and July. The status of this gull in Tamaulipas remains to be determined; probably it will be found breeding locally, but many of the birds summering in eastern México are most likely nonbreeders (A.O.U. Check-list, 1957:226).