Vertebrates from the Barrier Island of Tamaulipas, Mexico Part 1

Vertebrates from the Barrier Island of Tamaulipas, Mexico.

by Robert K Selander and Richard F Johnston and B. J. Wilks and Gerald G. Raun.

The Ecological Setting

The barrier island of Tamaulipas geologically and ecologically resembles Padre Island, of the Gulf coast of lower Texas, north of the mouth and delta of the Rio Grande. South of the delta, the island in Tamaulipas is a narrow strip of sand less than a mile in average width and is broken by a series of narrow inlets or "pa.s.ses" through which water from the Gulf of Mexico mingles with that of the Laguna Madre de Tamaulipas. The pa.s.ses are subject to recurrent opening and closing.

North of the mouth of the Rio Soto la Marina, eight pa.s.ses are designated by local fishermen, but only three, the Third, Fourth, and Fifth, were open at the time of our visit.

The Laguna Madre de Tamaulipas is described by Hildebrand (1958) in connection with a preliminary study of the fishes and invertebrates there. The average depth is probably less than 70 cm. and the waters are hypersaline. In the time of the recent drought in Texas and northeastern Mexico, salinity varied from 108 to 117 parts per thousand in the northern part of the laguna near Arroyo del Tigre (measurements taken in March, 1955) to from 39 to 48 parts per thousand in the southern part near Punta Piedras (measurements taken in October and November, 1953, and in March, 1954). Discussions of the geologic history, ecology, and zoogeography of the lagoons of the Gulf coast of the United States are given by Hedgpeth (1947; 1953).

Localities in coastal Tamaulipas mentioned in the text of this paper are shown on Plate 5.

The princ.i.p.al animal habitats are found in three vegetational a.s.sociations (plates 6 and 7). On flats and low dunes lying between, and partly sheltered by, larger active dunes, small clumps of _Croton punctatus_ and a sedge (_Fimbristylis castanea_) are the only conspicuous plants. Near the western edge of the dunes, _Ipomoea pescaprae_ var. _emarginata_ is mixed with _Croton_, and there are scattered clumps of shrubby wolf-berry (_Lycium carolinianum_ var.

_quadrifidum_), and mesquite (_Prosopis juliflora_).

The dunes are relatively stabilized on the western side of the island, and there we found moderately dense stands of mesquite trees reaching heights of from eight to 10 feet. p.r.i.c.kly-pear cactus (_Opuntia lindheimeri_) was common in those stands of mesquite, and we saw an occasional yucca tree. A fairly dense ground cover was formed by blanket-flower (_Gaillardia pulch.e.l.la_), marsh-elder (_Iva_ sp.), _Flaveria oppositifolia_, _Enstoma exaltatum_, and _Croton capitatus_ var. _albinoides_.

A more open, xeric expression of the mesquite-cactus vegetation occurs on exposed, low clay dunes (see description by Price, 1933) located on alkaline flats bordering the laguna. At the time of our visit, most of the mesquites in these stands were dead or dying, the cactus was abundant, and the ground cover, which was spa.r.s.e, included drop-seed (_Sporobolus virginicus_), ragweed (_Ambrosia psilostachya_), and _Commicarpus scandens_.

On alkaline flats flooded by hypersaline waters of the laguna following heavy rains, _Batis maritima_ is found in the lower areas, but on the slightly elevated areas there is low and almost continuous cover of _Monanthochloe littoralis_, in which can be found _Batis_, _Borrichia fructescens_, _Salicornia_ sp., _Iva_ sp., and sea-lavender (_Limonium carolinianum_).

Near Third Pa.s.s, sea oats (_Uniola paniculata_), evening primrose (_Oenothera_ sp.), and cordgra.s.s (_Spartina_ sp.) are present on the dunes, and on alkaline flats we collected _Conocarpus erectus_, _Leucaena_ sp., and _Ca.s.sia fasciculata_ var. _ferrisiae_.

Itinerary

We reached Washington Beach from Matamoros on July 6, and drove to a point approximately 33 miles south on the beach, where we made Camp 1 on the east side of large dunes 400 yards from the surf. From this camp we worked the beach and dunes and also visited alkaline flats adjacent to the Laguna Madre. On the afternoon of July 8, we drove south along the beach and established Camp 2 on the south side of the Third Pa.s.s, approximately 73 miles south of Washington Beach. We had intended to go farther south but were unable to cross the Fourth Pa.s.s, an inlet three miles south of the Third Pa.s.s. We left the barrier island on the afternoon of July 10, after driving north from Camp 2 to the mouth of the Rio Grande, 11 miles north of Washington Beach.

Mexican fishermen camped at the Fourth Pa.s.s told us that, had we been able to cross the Fourth Pa.s.s, it would have been possible to drive south on the beach all the way to La Pesca, a fishing village near the mouth of the Rio Soto la Marina, approximately 150 miles south of Washington Beach.

Summary of Previous Work in the Area

The ornithologist H. E. Dresser (1865-1866) worked in southern Texas and at Matamoros, Tamaulipas, in 1863, and on one occasion reached the mouth of the Rio Grande ("Boca Grande"). He did not visit the barrier island or the Laguna Madre de Tamaulipas.

In their extensive travels through Mexico, E. W. Nelson and E. A.

Goldman made collections at three localities in the coastal region of Tamaulipas but did not reach the barrier island (Goldman, 1951).

Goldman collected at Altamira, near Tampico, from April 2 to 24, 1898, and from May 15 to 20 of the same year both he and Nelson made headquarters at Altamira. Nelson and Goldman also collected in the vicinity of Soto la Marina, 25 miles from the coast, from March 1 to 10, 1902, and, from February 13 to 15, they visited Bagdad, described by Goldman (1951:260) as "a village at very low elevation on the Rio Grande about 6 miles above the mouth of the river."

In March, 1950, C. von Wedel and E. R. Hall collected four species of mammals and one bird on the barrier island at Boca Jesus Maria (Eighth Pa.s.s). A report of this work published by Hall (1951) contains descriptions of three new subspecies of mammals from the island.

A few records of birds from the southern end of the barrier island and from other parts of coastal Tamaulipas were reported by Robins, Martin, and Heed (1951). In 1953, R. R. Graber and J. W. Graber made ornithological studies in the vicinity of Tampico and also reached the western edge of the Laguna Madre de Tamaulipas. Several papers on this work have appeared (Graber and Graber, 1954_a_, 1954_b_; Graber, 1955), but a comprehensive account of their observations and specimens was not published. Finally, J. R. Alcorn collected some sandpipers 20 miles southeast of Matamoros, on August 21, 1954, obtaining the first record of the Semipalmated Sandpiper (_Ereunetes pusillus_) in Tamaulipas (Thompson, 1958).

Accounts of Species

Catalogue numbers in the following accounts are those of the Museum of Natural History, The University of Kansas.

_Reptiles_

=_Gopherus berlandieri_= Aga.s.siz: Texas Tortoise.--A pelvic girdle and complete sh.e.l.l with a few attached scutes (63494) were found in stabilized dunes at Camp 1 on July 7, and tracks were seen in the same area. Fragments of two other sh.e.l.ls (63493, 63495) were found on sand flats between active dunes at Camp 1.

=_Holbrookia propinqua propinqua_= Baird and Girard: Keeled Earless Lizard.--This lizard was abundant on dunes and in pebble-strewn blow-out areas between dunes at Camp 2, but it occurred in smaller numbers in the less stabilized dunes of spa.r.s.er vegetation at Camp 1.

Breeding was in progress at both localities, as evidenced by the presence of eggs in the oviducts of several females, by the heightened coloration of both s.e.xes, and by mating behavior.

The mating behavior of this species has not been described in the literature, and the following observations, made by Raun at Camp 2 on July 8, may be of interest. A male was seen to circle a female as the latter remained motionless with tail curved upward and to the side, exposing a patch of bright pink-orange color on the ventral surface of the tail. At times the male approached the female from the rear and slightly to the side, biting the dorsal part of her neck and simultaneously attempting to effect intromission. The female several times reacted to this approach by running forward a few steps, thereby freeing her neck from the grasp of the male. When the male did not attempt to approach again, the female appeared to invite copulation by moving in front of him with tail elevated and the colored ventral surface prominently displayed. At the time of copulation, the male mounted from the rear on the right side of the female, grasped her neck, and circled his tail beneath her tail; at the same time the hindquarters of the female were arched upward.

To confirm the presumed s.e.xes of the two individuals under observation, both were collected while in copulation. Examination of the still-coupled specimens showed that both hemipenes of the male were everted and the left one had been inserted.

Apparently the pink-orange subcaudal patch of females is present only in the mating season. It was not present on specimens of this species taken by Raun and Wilks on Padre Island, Texas, in autumn, and it is not mentioned in taxonomic descriptions by Axtell (1954) and Smith (1946).

Measurements of adult specimens in our series indicate that females are of smaller average size than males, and, as previously noted by Smith (1946:132), females of this species have disproportionately shorter tails than do males (Table 1).

_Holbrookia propinqua_ was previously collected on the barrier island by Axtell (1954:31; see also Axtell and Wa.s.serman, 1953:2), who took specimens at Boca Jesus Maria, at a locality six to seven miles south of Boca Jesus Maria, and at a point 20 miles east-southeast of Matamoros. Axtell (_loc. cit._) also lists specimens in the Museum of Zoology, University of Michigan, from Tepehuaje and from one mile north of Miramar Beach (Tampico).

Specimens (56): 3 [M] [M] adult, 1 [M] subadult, 63433-436, Camp 1, July 7. 33 [M] [M] adult, 63437-440, 63443-445, 63447, 63448, 63450-456, 63458, 63460, 63462, 63463, 63465-468, 63470-478; 13 [F]

[F] adult, 63441, 63446, 63449, 63457, 63459, 63469, 63479-485; 6 juv., 63442, 63461, 63464, 63486-488; Camp 2, July 9-July 10.

TABLE 1.--MEASUREMENTS IN MILLIMETERS OF ADULT SPECIMENS OF _Holbrookia propinqua_ FROM THE BARRIER ISLAND OF TAMAULIPAS

=======+===========+=============+==========+=============== Number Ratio: s.e.x of Snout-vent Tail snout-vent specimens length length to tail -------+-----------+-------------+----------+--------------- Male 33 56.00.5[A] 77.00.7 0.7310.001 (49-62) (69-85) (0.682-0.817) -------+-----------+-------------+----------+--------------- Female 14 50.90.5 62.20.9 0.8250.001 (47-53) (57-68) (0.735-0.877) -------+-----------+-------------+----------+---------------

[Footnote A: Mean standard error; range indicated in parentheses.]

=_Cnemidophorus gularis_= Baird and Girard: Whip-tailed Lizard.--At both camps we found this species in the same general habitat in which _Holbrookia_ occurred, but in numbers decidedly fewer than the latter.

Specimens (4): 2 [F] [F] adult, 63489, 63490, Camp 1, July 7. 1 [M]

adult, 63491, 1 [F] adult, 63492, Camp 2, July 9.

We failed to take specimens of snakes on the barrier island, but tracks of snakes were noted on two occasions in dunes near Camp 1; one trail led into a burrow of a kangaroo rat.

_Birds_

Unless otherwise indicated, specimens taken were not molting. For birds undergoing postnuptial or postjuvenal molt, the degree of advancement of the molt is indicated by recording the number of primaries of the old plumage that have not been dropped. For example, the designation "4 P old" signifies that all primaries except the distal four have been molted.