Vertebrates from the Barrier Island of Tamaulipas, Mexico Part 3

=_Eremophila alpestris giraudi_= (Henshaw): Horned Lark.--This species occurred in moderate numbers on alkaline flats and almost barren sand flats at both camps. At the time of our visit to the island, the breeding season apparently was coming to an end, but we noted no tendency in the birds to flock.

Specimens (7): [M], 38981, testis 6 mm., 21.0 gm.; [M], 38977, testis 7.5 4 mm., not fat, 27.5 gm.; [M], 38979, testis 11 7 mm., 29.0 gm.; [F], 38976, ova to 3 mm., brood patch vascular but regressing, no fat, 24.4 gm.; s.e.x? juv., 38987, no fat, 21.0 gm.; s.e.x? juv., 38980, 24.0 gm.; Camp 1, July 7. Male, 38982, testis 9.5 6 mm., 27.5 gm., Camp 2, July 9.

The subspecies _E. a. giraudi_, which is endemic to the Gulf coastal plain of Texas and Tamaulipas, has been reported in Tamaulipas previously only from Bagdad, near Matamoros (Mexican Check-list, 1957:106). The fact that our specimens show characters totally consistent with those of _E. a. giraudi_ indicates that there is little genetic interchange between the population we sampled and those of _E.

a. diaphora_, the closest of which reportedly breeds at Miquihana, in southwestern Tamaulipas.

=_Corvus cryptoleucus_= Couch: White-necked Raven.--Several groups of six to ten birds were present at Was.h.i.+ngton Beach on July 6 and 10; but, southward on the island, we recorded this species only once, on July 9, when a lone individual flew near Camp 2, being pursued and "buzzed" by two Least Terns. The Mexican Crow (_Corvus imparatus_) reportedly is common in the coastal region of Tamaulipas (Mexican Check-list, 1957:118) but was not seen by us.

=_Thryomanes bewickii cryptus_= Oberholser: Bewick Wren.--This species seemingly breeds in small numbers in mesquite stands near Camp 1, where we obtained a juvenile and saw another individual. Specimen: [F] juv., 38983, no fat, 10.0 gm., Camp 1, July 8. _T. b. cryptus_ is reported to intergrade with _T. b. murinus_ of Veracruz in southern Tamaulipas (Mexican Check-list, 1957:160-161).

=_Mimus polyglottos leucopterus_= (Vigors): Northern Mockingbird.--We recorded this species only near Camp 1, where a few pairs were breeding in stands of mesquite. Males were in full song and territorial display.

Specimens (2): [M], 38985, testis 11 7 mm., not fat, 43 gm.; [F], 38984, ova to 4.5 mm., vascular brood patch, 49.0 gm.; Camp 1, July 7.

PLATE 7

[Ill.u.s.tration: FIG. 1.--Mesquite-cactus formation on clay dune at margin of the Laguna Madre west of Camp 1. Habitat of Northern Mockingbird, Cardinal, Bob-white, black-tailed jackrabbit, and Great Plains woodrat.]

[Ill.u.s.tration: FIG. 2.--_Batis-Monanthochloe_ formation on alkaline flats near the Laguna Madre, with mesquite bordering stabilized dunes in the left background. _Salicornia_, a cla.s.sical dominant of salt marshes, is here relatively inconspicuous. Habitat of Nighthawk and Horned Lark.]

PLATE 8

[Ill.u.s.tration: "Fossilized" burrow of Texas Pocket Gopher in a sandy trough between active dunes. A part of the cast has been broken away to show the general shape of the old burrow. The diameter of the cast is about 3.5 inches.]

=_Ca.s.sidix mexica.n.u.s prosopidicola_= Lowery: Great-tailed Grackle.--Small, postbreeding flocks composed of both adult and juvenal birds were seen moving along the edge of the laguna at Camp 1. In the morning the flocks flew south, and in the afternoon groups of similar size flew north, presumably to a roost at an undetermined distance north of our camp. Occasionally, a few birds stopped to rest or to forage on the dunes or in stands of mesquite. At Camp 2 on July 9, a postbreeding adult female and a well-grown, presumably independent juvenile were taken as they perched in a clump of mesquite in which we found three old nests of _Ca.s.sidix_; two of the nests were about four feet apart in one tree, and the third was in another tree 100 feet from the first.

Specimens (4): [M] adult, 38988, testis 6 mm., no fat, 209 gm., 6 P old, Camp 1, July 7. Female, 38989, ova to 3 mm., fat, 115 gm., old brood patch, Camp 1, July 8. Female, 38990, ova to 1 mm., moderate fat, 107 gm., 7 P old, brood patch refeathering; [M] juv., 38991, testis 3 1 mm., not fat, 172 gm., 6 P old; Camp 2, July 9.

TABLE 4.--MEASUREMENTS IN MILLIMETERS OF ADULT MALES OF Ca.s.sIDIX MEXICa.n.u.s

=============+=========+=========+=========+===========+============ Weight in LOCALITY No. Wing Tail Tarsus grams -------------+---------+---------+---------+-----------+------------ Austin, Texas 17-137[1] 184.3 203.8 46.38 225.6 June (173-200) (178-232) (41.8-50.0) (204-253) 202.2 July (195-207) San Patricio 5 185.2 204.2 46.74 237.6 Co., Texas[2] (182-188) (190-219) (45.1-50.2) (228-245) Barrier Is., Tamps. 1 178 185 47.1 209 Victoria, 4 192.2 224.2 47.77 254.3 Tamps.[3] (186-200) (215-232) (46.0-49.1) (239-276) Tampico, Tamps.[4] 1 197 214 48.3 260 Catemaco, Veracruz[5] 1 193 216 48.2 257 -------------+---------+---------+---------+-----------+------------

[Footnote 1: Data from Selander (1958: 370, 373). Sample sizes, as follows: wing, 137; tail, 119; bill length, 20 (June and July); tarsus, 133; weight, 17 for June, 3 for July.]

[Footnote 2: June 13, 1961; breeding condition.]

[Footnote 3: May 6, 1961; breeding condition.]

[Footnote 4: May 7, 1961; breeding condition.]

[Footnote 5: November 28, 1959.]

Specimens from the barrier island are clearly referable to _C. m.

prosopidicola_, showing no approach to the larger and, in the female, darker _C. m. mexica.n.u.s_ of Veracruz and San Luis Potosi. In Table 4, measurements of the adult male from the barrier island may be compared with those of specimens of _C. m. prosopidicola_ from Texas and a specimen of _C. m. mexica.n.u.s_ from Veracruz; it is apparent that our specimen is a.s.signable to the former.

Evidence of intergradation between the two subspecies is shown in a series of birds collected near Ciudad Victoria, Tamaulipas, in May, 1961. The females in the series are highly variable in color individually, but are on the average paler than _C. m. mexica.n.u.s_ from Veracruz; the males are distinctly larger than _C. m. prosopidicola_ from Texas. At Miramar, near Tampico, Tamaulipas, a decided approach to _C. m. mexica.n.u.s_ is also evident in the dark color of females and in the large size of both males (Table 4) and females.

=_Agelaius phoeniceus megapotamus_= Oberholser: Red-winged Blackbird.--This species was recorded only at Camp 1 on July 7, when we saw two males, one of which was flying south along the edge of the dunes in a flock of five Great-tailed Grackles. Specimen: [M], 38992, testis 10 7 mm., fat, 54 gm., Camp 1, July 7. The large size of the testes of this individual indicates breeding condition.

=_Sturnella magna hoopesi_= Stone: Eastern Meadowlark.--Meadowlarks were found in small numbers along the margins of the alkaline flats at both camps. Breeding was still in progress, for males were singing and a female shot on July 9 had only recently laid eggs. Specimens (2): [M], 38986, testis 13 8 mm., not fat, 102 gm.; [F], 38987, ova to 6 mm., 3 collapsed follicles, not fat, 88 gm.; Camp 2, July 9.

=_Richmondena cardinalis canicaudus_= Chapman: Cardinal.--This species was recorded only in stands of mesquite near Camp 1, as follows: July 7, two pairs seen, from which a breeding female was taken; July 8, three birds seen. Specimen: [F], 38933, edematous brood patch, 36.5 gm., Camp 1, July 7. Intergrades between the present subspecies and _R.

c. coccinea_ of Veracruz are reported from Altamira, Tamaulipas (Mexican Check-list, 1957:329).

_Mammals_

=_Dasypus novemcinctus mexica.n.u.s_= Peters: Nine-banded Armadillo.--Remains of an armadillo (89017) were found in a mesquite thicket in the dunes near Camp 1 on July 7. The bones are not badly weathered and were not embedded in sand.

This species has not been recorded previously on the barrier island of Tamaulipas, nor, for that matter, on any of the barrier islands on the western sh.o.r.e of the Gulf of Mexico.

=_Lepus californicus merriami_= Mearns: Black-tailed Jackrabbit.--From two to four individuals were recorded daily in dunes and on alkaline flats in the vicinity of stands of mesquite and cactus.

Specimens (2): [F] adult, 89018, pregnant (two embryos, 28 mm. in crown-rump length), Camp 1, July 6. Male immature, 89019, Camp 1, July 7. Our specimens have been compared with two skins of _L. c. curti_ from the type locality at Eighth Pa.s.s, with which they agree reasonably well in color. The size of the adult female is about that characteristic of other specimens of adult _L. c. curti_, but characters of the skull are consistent with those of _L. c. merriami_.

A specimen of this species from Matamoros and several from Brownsville, Texas, have been a.s.signed by Hall (1951:43) to _L. c. merriami_.

Specimens from Padre Island, Texas, reportedly resemble _L. c. curti_ in smallness of the tympanic bullae but are in other characters referable to _L. c. merriami_ (Hall, 1951:44).

=_Spermophilus spilosoma annectens_= (Merriam): Spotted Ground Squirrel.--These squirrels were moderately common in dunes at both camps. They were heard calling, and many tracks and holes were seen. On July 7, at Camp 1, a lactating, adult female (89020) and two dependent juveniles (89021, skull only, 89022, skin and skull) were shot at the entrance of a burrow; the uterus of the adult showed six placental scars.

Our adult specimen has been compared with ten specimens obtained by Hall and von Wedel at Eighth Pa.s.s in March, 1950; ours differs from the ten in being paler and slightly larger. The pallor is perhaps attributable to seasonal variation, and the size (246-79-38-7; weight, 133 gm.) is within limits that would be expected in a larger series of the population sampled by Hall and von Wedel. Hall (1951:38) referred specimens of this squirrel from Eighth Pa.s.s to _S. s. annectens_.

=_Geomys personatus personatus_= True: Texas Pocket Gopher.--This pocket gopher was abundant on low, stabilized dunes on the barrier island from four to 73 miles south of Was.h.i.+ngton Beach. One of us (Wilks) made a trip down the beach on May 20 and 21, 1961, and collected specimens at localities four miles south and 33 miles south of Was.h.i.+ngton Beach; additional specimens were taken at both Camp 1 and Camp 2 from July 6 to 10. At these localities the gophers seemed to maintain population densities approximating those of _G. personatus_ on Padre and Mustang islands on the Texan coast.

There is but one other record of the Texas Pocket Gopher from Mexico.

Goldman (1915) described _G. p. tropicalis_ from Altamira on the basis of specimens collected in 1898. Since that time, the species has not been reported as occurring south of Cameron County, Texas (Kennerly, 1954), some 50 miles northwest of the closest station of occurrence of the gophers on the barrier beach of Tamaulipas.

Our specimens are slightly smaller than _G. p. personatus_ and slightly larger than _G. p. megapotamus_, the subspecies of nearest geographic occurrence to the barrier island. The degree to which our specimens differ in other respects, such as configuration of the pterygoid, is being studied further by Wilks. For the present, reference of our material to the nominate subspecies best expresses the relations.h.i.+ps of these coastal gophers.

The fact that pocket gophers from the Tamaulipan barrier island occupy a position geographically intermediate between present Texan populations and the isolated population in southern Tamaulipas (_G. p.

tropicalis_) helps explain the origin of the latter. It is likely that _G. p. tropicalis_ represents the southern remnant of a once continuously-distributed population of pocket gophers living in coastal Tamaulipas in mid-Wisconsin to late Wisconsin time. At that time, sea level is thought to have been considerably lower than at present, exposing a sandy strip 80 to 100 miles wide off the present coastline.

Presumably this would have been an area suitable for gophers and for southward dispersal of individuals from Texas. The only conceivable barrier to dispersal, and thus to a panmictic population, would have been the Rio Grande, but over the wide, low and sandy coastal plain the river channel almost certainly s.h.i.+fted regularly, thus decreasing its effectiveness as a barrier to movement. With subsequent rise in sea level, the gophers at Altamira became isolated and have presumably remained so for a considerable time. To judge by the marked morphologic differentiation of _G. p. tropicalis_, its degree of isolation from other populations has been much greater than those of populations inhabiting the Tamaulipan barrier island and the barrier islands of the coast of Texas. Contact between the latter two populations was probably fairly regular before man's stabilization of the channel of the lowermost reaches of the Rio Grande.

At Camp 1 we found evidence of the former occurrence of gophers in an area now largely covered by active beach dunes. Numerous skeletal parts of gophers and "fossilized" burrows (Plate 8) were found on the surface where troughs between active dunes reached down to an older, darker, and more tightly cemented layer of sand underlying the present dunes.

It is clear that these gophers were not transported there, because the bones were not damaged, some of the skeletons were almost complete, and many of the bones were found near the "fossilized" burrows. Weathered but well preserved skeletal remains of at least 12 gophers were picked up at this site.

Specimens (17): [F], 89023, Camp 1, May 20. 4 [F] [F], 89024-026, 89029; 3 [M] [M], 89027, 89028, 89030; Camp 1, May 21. Male, 89031, Camp 1, July 6. Three [M] [M], 89032, 89035, 89038; 4 [F] [F], 89033, 89034, 89036, 89037; Camp 2, July 9. Female, 89039, Camp 2, July 10.

=_Perognathus merriami merriami_= Allen: Merriam Pocket Mouse.--An individual taken in a trap in the dunes near Camp 2 const.i.tutes the first record of this species from the barrier island of Tamaulipas.

This pocket mouse seems to be uncommon on other barrier islands of the western Gulf of Mexico, for there is only one published report of its occurrence on Padre Island, Texas (Bailey, 1905:141). Other nearby stations of occurrence are Altamira, Tamaulipas (Hall and Kelson, 1960:477), Brownsville, Texas (Bailey, _loc. cit._), and 17 miles northwest of Edinburg, Texas (Blair, 1952:240).

Specimen: s.e.x?, 89040, skull only, Camp 2, July 10.

=_Dipodomys ordii parvabullatus_= Hall: Ord Kangaroo Rat.--We found this species uncommon and confined in distribution to dunes, in which it was recorded as follows: an adult female was shot and two other individuals were seen at night on July 6 at Camp 1; three were trapped near Camp 1 on July 7; two were trapped at Camp 2 on July 10.

Specimens (5): [F], 89041, 2 placental scars, 46 gm., Camp 1, July 6.

Male, 89042, testes scrotal, 47 gm.; [M], 89044, 60 gm.; [F], 89043, 44 gm.; Camp 1, July 7. s.e.x?, 89045, skel. only, Camp 2, July 10.

Our material does not differ significantly from specimens obtained by Hall and von Wedel at Boca Jesus Maria in March, 1950, which formed the basis for Hall's description (1951:41) of _D. o. parvabullatus_. This subspecies is presumably confined in distribution to the barrier island of Tamaulipas. Two immature specimens from Bagdad, Tamaulipas, were tentatively a.s.signed by Hall (1951:41) to _D. o. compactus_, a subspecies known otherwise only from Padre Island, Texas.