Vertebrates from the Barrier Island of Tamaulipas, Mexico Part 2

On the basis of the evidence presently available, we are reluctant to follow Sutton (1950:136) in a.s.signing breeding birds from the Gulf coastal region to _C. s. inornatus_, a name otherwise applied to a population of birds breeding inland, in northwestern North America south to central Utah and Colorado and east to South Dakota (and formerly to western and southeastern Minnesota and Iowa; see A.O.U.

Check-list, 1957:190). The intermediate characters of birds breeding in coastal Texas and Tamaulipas probably represent not the results of actual genetic intermixing of the two named populations but, rather, an adaptive response of the eastern coastal stock (_C. s. semipalmatus_) to environmental modalities distinct from those operating elsewhere within the range of the eastern coastal population or on the inland population. Accordingly, we tentatively use the name _C. s.

semipalmatus_ for our Tamaulipan specimens, realizing that the patterns of geographic variation in the species do not lend themselves well to taxonomic treatment by the trinomial nomenclatural system. The need for a comprehensive a.n.a.lysis of geographic variation in this species, based, if possible, on proper segregation of age cla.s.ses along the lines followed by Pitelka (1950) for _Limnodromus_, is obviously indicated.

PLATE 5

[Ill.u.s.tration: Map of coastal Tamaulipas, showing the barrier island and localities mentioned in text. Stippled areas are extensively marshy.]

PLATE 6

[Ill.u.s.tration: FIG. 1.--_Croton_ and _Fimbristylis_ on stabilized dunes; the Laguna Madre and surrounding alkaline flats and clay dunes are visible in the background. Habitat of Road-runner, Ord kangaroo rat, and keeled lizard.]

[Ill.u.s.tration: FIG. 2.--Active dune near Camp 1. Other active dunes can be seen in the background, in the right foreground is a clump of _Croton_, and in the left foreground is a small clump of _Fimbristylis_. Habitat of Road-runner, Ord kangaroo rat, and keeled lizard.]

=_Arenaria interpres morinella_= (Linnaeus): Turnstone.--Approximately 40 individuals were noted along the beach from July 6 to 10, mostly in small groups; the largest flock included 15 individuals. Specimens (5): [M], 38931, testis 4 1 mm., moderately fat, 107 gm., 4 P old; [M], 38932, testis 3 1 mm., moderately fat, 103 gm., molting; 75 miles south of Washington Beach, July 8. Male, 38928, testis 2 mm., 111 gm., 3 P old; [M], 38929, testis 3 mm., moderately fat, 106 gm., 6 P old; [M], 38930, testis 2.5 mm., moderately fat, 108 gm., 6 P old; Camp 2, July 9.

The only previous record of the Turnstone in Tamaulipas is an observation of an unspecified number at Tepehuaje on May 9, 1949 (Robins, Martin, and Heed, 1951). The dates of our records suggest that nonbreeding birds summer along the coast of Tamaulipas. The species is present in small numbers in summer along the central Gulf coast of Texas (Hagar and Packard, 1952:8). Loetscher (1955:26-27) does not report records for Veracruz in summer, but records of the species in Yucatan on May 31, 1952 (Paynter, 1955:101), and on June 16, 1900 (Mexican Check-list, 1950:79), probably represent summering nonbreeders. Probably also in the same cla.s.s are supposed "migrants"

seen at Coatzacoalcos on May 17, 1954, and June 4, 1955 (Coffey, 1960:290).

Inasmuch as Haverschmidt (1955:368) reports that nonbreeding birds summering in Surinam only occasionally a.s.sume breeding plumage, it is noteworthy that our specimens were molting from nuptial (summer) to winter plumage. None of the nonbreeding northern sh.o.r.ebirds observed by Eisenmann (1951:183) in Panama in summer were in nuptial plumage.

=_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): [M], 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; [M], 38939, fat, no weight recorded, 6 P old, breeding plumage; 3 [M] [M], 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 Mexico 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): [M], 38934, testis 2.5 mm., heavy fat, 116 gm., 4 P old; [M], 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 Mexico before August (Mexican Check-list, 1950:101). The species is known to breed in San Luis Potosi (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 pa.s.ses 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): [M] subadult, 38944, testis 5 1 mm., 325 gm., molting; [F], 38945, ovary small, 309 gm., in molt, brood patches refeathering; s.e.x?, 38943, 315 gm., in molt; s.e.x? 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 Mexico 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 Mexico are most likely nonbreeders (A.O.U. Check-list, 1957:226).

=_Chlidonias niger surinamensis_= (Gmelin): Black Tern.--On July 6, 7, 8, 9, and on the morning of July 10, we saw this species only occasionally, recording in total not more than 50 individuals. But, about noon on July 10, we observed at least 300 birds in compact flocks of about 50 individuals each between Washington Beach and a point about 9 miles south of that locality. Approximately one in ten birds seen was in breeding plumage, the rest being in winter or subadult plumages, which are indistinguishable in the field. Perhaps some of the birds seen were nonbreeding, summering individuals, but we presume that the large groups were southbound migrants, and we note that autumnal migrants appear in northern Veracruz as early as July 1 (Loetscher, 1955:30). On the central Gulf coast of Texas, Hagar and Packard (1952:9) indicate that an influx of birds occurs in the last week of July, and small numbers of birds, presumably nonbreeding individuals, are present along the Gulf coast throughout June and July. Dresser (1866:45) found this species to be "common at the Boca Grande during the summer."

Specimens (2): [M], 38948, testis 6 mm., moderately fat, 68 gm., in breeding plumage, Camp 1, July 7. Female, 38949, ovary inactive, 49 gm., molt into winter feather almost complete, Camp 2, July 10.

=_Hydroprogne caspia_= (Pallas): Caspian Tern.--The only published record of the Caspian Tern in Tamaulipas is a report of one seen at Lomas del Real on November 20, 1956 (Coffey, 1960:260), but we found it moderately common all along the beach and at the margin of the laguna.

It was frequently a.s.sociated with the Royal Tern, which outnumbered it better than three to one (see Table 2). The species is resident and breeds along the coast of Texas, and it probably has similar status in Tamaulipas. However, in Veracruz it is known only as a winter visitant (Loetscher, 1955:30) and as a spring migrant (Coffey, 1960:293).

Specimen: [F], 38950, ova to 2 mm., moderately fat, weight not recorded, 5 P old, Camp 2, July 9.

=_Sterna hirundo hirundo_= Linnaeus: Common Tern.--We took a specimen ([M]?, 38951, no fat, 165 gm.), 49 miles south of Washington Beach on July 8, and saw two others over the laguna at Camp 2 on July 9. Our specimen had nearly finished with molt and feather growth into adult winter plumage. The status of Common Terns in Tamaulipas is uncertain; our record, and records from Tamos on July 1, 1952, and June 12, 1953 (Loetscher, 1955:29), probably pertain to nonbreeding, summering birds.

Yet, the species has bred on the Texas Gulf coast (A.O.U. Check-list, 1957:235), and it reasonably may be expected to nest in Tamaulipas.

Coffey (1960:293) saw two individuals at Altamira on May 10, 1954.

=_Sterna forsteri_= Nuttall: Forster Tern.--Six were recorded near Camp 1 on July 7, and two were seen on the beach on July 6 and 10. The Mexican Check-list (1950:108) does not cite records for Tamaulipas, but the A.O.U. Check-list (1957:234) includes northern Tamaulipas within the breeding range. Evidence suggesting breeding of the species in extreme northern Veracruz is reported by Loetscher (1955:29) in the form of a female specimen with "ovary greatly enlarged" taken seven miles west of Tampico on May 30, 1947. In the same area the species also seems to spend the summer as a nonbreeder, for Loetscher (_loc.

cit._) saw 20, nearly all in nonbreeding plumage, on July 1, 1952.

Specimens (4): [M], 38952, testis 4.5 mm., 150 gm., 8 P old; [M], 38955, testis 2 mm., 138 gm., 2 P old; [M], 38953, testis 5 1 mm., 142 gm., 5 P old; [F], 38954, ova to 1 mm., 148 gm., 2 P old; Camp 1, July 7.

=_Sterna albifrons antillarum_= (Lesson): Least Tern.--The status of this species in Tamaulipas is uncertain, but there is reason to believe that it breeds, at least in small numbers. We found the species moderately common and generally flying about in twos, possibly mated pairs, near both camps and on the beach. Breeding is suggested by the large sizes of the testes of the two males collected and by the presence of brood patches on a female taken on July 6, but we have no direct evidence of nesting in Tamaulipas, and it should be noted that this species is known to spend the summer in nonbreeding condition at many places (A.O.U. Check-list, 1957:239). Loetscher (1955:30) suggests that the species may be found breeding in Veracruz and mentions a record of 15 seen at Miramar, Tamaulipas, on June 26, 1952. Dresser (1866:45) found it to be "abundant" at the "Boca Grande" in summer.

On July 10, we saw flocks of 15 to 20 individuals flying along the beach a few miles south of Washington Beach.

Specimens (4): [M], 38958, testis 11 4 mm. (right testis 5 4 mm.), light fat, 45 gm., 6 P old; [M], 38959, testis 11 4 mm. (right testis 7 4 mm.), light fat, 45 gm., 6 P old; [F], 38956, ova to 2.5 mm., 42.5 gm., 6 P old, brood patches refeathering; Camp 1, July 6. Female, 38957, ova to 1 mm., 44 gm., Camp 1, July 7. This last specimen had essentially completed the autumnal molt into winter plumage, with only a few feathers remaining ensheathed basally.

Our specimens are referable to _S. a. antillarum_, being paler dorsally and slightly lighter gray on the hind-neck than specimens of _S. a.

athala.s.sos_ from Kansas, with which they were compared.

=_Thala.s.seus maximus maximus_= (Boddaert): Royal Tern.--This species was common all along the beach, occurring for the most part in flocks of from ten to 50 individuals in a.s.sociation with Cabot Terns. Data on gonadal condition and brood patches of some of our specimens suggest that breeding occurs in coastal Tamaulipas, as previously reported by the Mexican Check-list (1950:110). Robins, Martin, and Heed (1951) report seeing one Royal Tern near Tepehuaje on May 9, 1949, and Dresser (1866:44) found the species "common at the Boca del Rio Grande during the summer."

Specimens (6): [M], 38960, testis 9 4.5 mm., not fat, 484 gm., 6 P old, brood patches refeathering, 4 miles south of Washington Beach, July 6. Male, 38961, testis 7 3 mm., 455 gm., no brood patches, 8 miles south of Washington Beach, July 6. Male, 38962, testis 10 5 mm., 387 gm., brood patches refeathering; [F], 38963, ova to 1 mm., 358 gm., 3 P old; [F], 38964, ova to 3 mm., 389 gm., 8 P old; Camp 1, July 7. Female, 38994, ova to 2 mm., 536 gm., brood patches refeathering, Camp 2, July 10.

=_Thala.s.seus sandvicensis acuflavidus_= (Cabot): Cabot Tern.--This tern was moderately common along the beach and margin of the laguna, and it was seen frequently in company with Royal Terns. Like the latter, this tern breeds in coastal Texas (A.O.U. Check-list, 1957:241), and it probably also nests in Tamaulipas, although direct evidence is not available. The only previous record of this species in Tamaulipas is a report (Robins, Martin, and Heed, 1951) of two observed on the beach near Tepehuaje on May 9, 1949.

Specimens (4): [M], 38965, testis 9 4.5 mm., 208 gm., 9 P old, 49 miles south of Washington Beach, July 8. Male, 38966, testis 8 3 mm., not fat, 192 gm., 8 P old; [F], 38967, ova to 3 mm., 193 gm., 7 P old, brood patches refeathering; [F], 38968, ova to 1 mm., 186 gm., 8 P old, no brood patches; 52 miles south of Washington Beach, July 8.

=_Rynchops nigra nigra_= Linnaeus: Black Skimmer.--We found this species moderately common at the edge of the laguna at both camps and occasionally saw it along the beach. Generally two birds, probably mated pairs, were seen together; twice birds were seen carrying food in their bills, presumably intended for nestlings. The species is known to nest in Tamaulipas from "Matamoros Lagoon" south to Tampico (Mexican Check-list, 1950:112).

Specimens (2): [M], 38970, testis 40 23 mm. (abnormally large, possibly as a result of hemorrhage), 418 gm., brood patches refeathering; [M], 38969, testis 17 4 mm., fat light, 442 gm., brood patches refeathering; Camp 1, July 7.

=_Zenaidura macroura_= Linnaeus: Mourning Dove.--Our only record is a lone bird seen in a mesquite near Camp 1 on July 6. Possibly the species breeds along the margin of the laguna, although Aldrich and Duvall (1958:113, map) do not include coastal Tamaulipas in the known breeding range. Loetscher (1955:30) suggests that the Mourning Dove may be found breeding in the lowlands of northern Veracruz and cites a record of one seen at Tamos on July 1, 1952.

=_Geococcyx california.n.u.s_= (Lesson): Road-runner.--At least four individuals were seen in large dunes at Camp 1 on July 7 and 8. On several occasions we watched them pursue lizards (_Holbrookia propinqua_) at the margins of clumps of _Croton_ and _Ipomoea_.

=_Chordeiles minor aserriensis_= Cherrie: Nighthawk.--Nighthawks of this species were seen regularly at Camp 1, where we flushed them from alkaline flats in the day and heard them calling as they foraged over the dunes in late afternoon.

Specimens (3): [M], 38971, testis 5 mm., no fat, 62 gm., Camp 1, July 6. Male, 38972, testis 7.5 mm., no fat, 58 gm.; [M], 38973, testis ?, no fat, 53 gm.; Camp 1, July 7. The gonads of these birds were not in full breeding condition, but it is highly probable that the birds were members of a population that had bred in the area.

Variation in _Chordeiles minor_ in Tamaulipas has recently been studied by Graber (1955). Two specimens taken by him on August 3, 1953, approximately 9 miles south of Carb.o.n.e.ra, resemble birds from Terrell County, Texas, and represent _C. m. aserriensis_, as do our three birds from the barrier island. Two of Graber's specimens from Lomas del Real, in southeastern Tamaulipas, are distinctly darker and probably represent _C. m. neotropicalis_, a subspecies subsequently described from Chiapas (Selander and Alvarez del Toro, 1955).

=_Muscivora forficata_= (Gmelin): Scissor-tailed Flycatcher.--On July 7 near Camp 1, two individuals were found in stands of mesquite. One was taken and proved to be an adult male (38974, testis 6 3 mm., not fat, 40 gm.) in postnuptial molt (6 P old).

We presume that the two birds recorded by us were members of a population breeding on the barrier island, rather than autumnal migrants. The Mexican Check-list (1957:69) records this species in Mexico only as a transient and winter visitant. But, on the basis of records of birds seen along the highway between Matamoros and Ciudad Victoria, Davis (1950) has suggested that the species breeds in Tamaulipas, and this is supported by a report of one seen at the north end of the Monterrey Airport on June 1, 1957 (Coffey, 1960:294). Brown (1958) has recently established that the species breeds in Nuevo Leon by finding a nest 33 kilometers (by road) north of Sabinas, Hidalgo, on July 19, 1954.

=_Myiarchus cinerascens cinerascens_= (Lawrence): Ash-throated Flycatcher.--A juvenal male (38975, testis 2 mm., no fat, 35.0 gm.) taken in mesquite at Camp 1 const.i.tutes our only record for this species. Lanyon (1961:441, map) has shown that most of Tamaulipas is devoid of these flycatchers in the breeding season; the nearest known breeding Ash-throated Flycatchers are slightly west of Corpus Christi, Texas, about 200 miles north-northwest of Camp 1 on the barrier beach.

Our specimen closely resembles eight specimens from Coahuila, Mexico, in general coloration and, especially, in the pattern of colors on the outer rectrices. Probably No. 38975 was from southwestern Texas or Coahuila and had begun its southward migration. Against this idea lies chiefly the fact that young-of-the-year tend to move south later than adults of the same species; so, this bird possibly had been reared in coastal Tamaulipas.