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قراءة كتاب North American Yellow Bats, 'Dasypterus,' and a List of the Named Kinds of the Genus Lasiurus Gray

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North American Yellow Bats, 'Dasypterus,' and a List of the Named Kinds of the Genus Lasiurus Gray

North American Yellow Bats, 'Dasypterus,' and a List of the Named Kinds of the Genus Lasiurus Gray

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دار النشر: Project Gutenberg
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generally like those of animals to the east but average somewhat paler (less brownish). The specimens seen from Louisiana seem to be intergrades between intermedius and floridanus but clearly are assignable to the latter.

Plot
Fig. 1. Condylocanine length plotted against length of forearm for specimens of the species Lasiurus intermedius.

The picture is less clear as regards bats from southeastern Texas (one specimen each from Colorado and Travis counties, and four specimens from Harris County). Five of the specimens have skulls (the Travis County specimen is a skin only) and of these, four are clearly assignable, on the basis of size and shape of the skull, to intermedius. The fifth skull (specimen from Colorado County) is intermediate in size between floridanus and intermedius and on that basis alone could be assigned with equal propriety to either. All these specimens from Texas more closely resemble floridanus than intermedius in external size (forearms: 49.2, 49.6, 50.7, 49.9 (approximate), 49.6, 49.1). The pale yellowish-gray upper parts of the four adults, seemingly resulting from a dilution of the brownish color found in floridanus, differ from the color of typical specimens of both intermedius and floridanus, but the average is nearer that of floridanus than that of intermedius. Color of pre-adult pelage in the one July-taken young of the year resembles the color of adults. An August-taken young of the year is in process of acquiring the adult pelage but the hairs have not reached their full growth; it is pale yellowish but not so grayish as the other specimens. All characters considered, the specimens from eastern Texas resemble floridanus more than they do intermedius, and so are provisionally assigned to floridanus (as was done by Taylor and Davis, 1947:19; Eads, et al., 1956:440; and, Davis, 1960:59). Additional material from southeastern Texas is needed. It will be remembered that the type locality of intermedius is in the Rio Grande Valley; all specimens seen, in the study here reported on, from the Texas side of the valley are unquestionably referable to that subspecies.

Intergradation, then, occurs between L. intermedius and L. floridanus in some degree in southern Louisiana and in more marked degree in southeastern Texas. Specimens from the area of intergradation vary more individually in many features than do specimens from other areas. In general the intergrades tend to resemble floridanus in small size externally and intermedius in large size of skull. The specimens from southeastern Texas differ from typical specimens of both subspecies in color, being pale yellowish-gray (instead of yellowish to yellowish-orange as in intermedius or yellowish brown to brownish-gray as in floridanus), and this difference is shared to some extent with animals from Louisiana, the latter being somewhat intermediate between bats from Texas and those from Florida and Georgia, although nearer those from Florida and Georgia.

An hypothesis to account for the variation noted is that in Wisconsin Time, and perhaps in earlier Pleistocene times, this yellow bat was (as it is now) a warmth-adapted animal as Blair (1959:461) would term it. Some cool period forced the mainland populations of the two species into two refugia—peninsular Florida and eastern México—and the present area of intergradation is, therefore, of a secondary rather than a primary type. Possibly also the relatively treeless area of part of southern Texas has made for a sparse population there of Lasiurus intermedius and gene flow now may be, and long may have been, slight between the eastern and southern segments of the species.

It could be contended that the peculiar coloration of specimens from southeastern Texas, coupled with the tendency to have a large skull (as has intermedius) and small external dimensions (as has floridanus), justifies subspecific recognition for the animals that here are termed intergrades. But, judging by the specimens now available, such subspecific recognition would tend to obscure rather than clarify the geographic variation noted.

Life History

Probably bats of the species Lasiurus intermedius seek retreats primarily in trees (see Moore, 1949a:59-60) but Baker and Dickerman (1956:443) reported "approximately 45 yellow bats" concealed on July 22, 1955, "among dried corn stalks hanging from the sides of a large open tobacco shed" in the state of Veracruz. Young are born in late spring, three being the only number known except that Davis (1960:59) was told that in the vicinity of Mission, Texas, two was the usual number "born in May and June." Sherman (1945:194) reported a female with young (number not given) taken on June 7, 1918, at Seven Oaks, Florida, and another with three young taken on June 20, 1941, at Ocala, Florida. Lowery (1936:17) recorded a female, having three young, obtained on June 17, 1932, at Baton Rouge, Louisiana. A specimen taken on May 19, 1940, at Baton Rouge contained three embryos. Baker and Dickerman (loc. cit.) reported four adult females from Veracruz as lactating on July 22, 1955, but they were accompanied by flying young of the year and probably were near the end of the lactation period. Among specimens examined, juveniles are available by date as follows: 5 mi. N Baton Rouge, Louisiana (June 26, 1953); Palm Beach, Florida (July 6, 1950); and Izamal, Yucatán ("taken with mother" on July 28, 1910). Breeding probably takes place in autumn and winter; Sherman (op. cit.:196) reported males from Florida as sexually "mature" from the beginning of September to mid-February. Late winter segregation of sexes has been reported.

Subspecies

In the following accounts, localities of occurrence in each state are listed from north to south; if two lie in the same latitude, the westernmost is listed first. Localities that are italicized are not shown on the distribution map (Fig. 2), either because undue crowding of symbols would result or, in several cases, because we could not precisely place the localities. Length of forearm is the average of both forearms in individuals in which both forearms could be measured.

Lasiurus intermedius intermedius (H. Allen)

1862. Lasiurus intermedius H. Allen, Proc. Acad. Nat. Sci. Philadelphia, 14:246, "April" (between May 27 and August 1), type from Matamoros, Tamaulipas.

Geographic distribution.—Southern México (Yucatán, Chiapas and Oaxaca), northward along Gulf Coast to Rio Grande Valley of southern Texas (see Fig. 2).

Diagnosis.—Size medium (see measurements); sagittal crest present (height above braincase averaging 0.4 mm. in 12 from Brownsville, Texas); interorbital region relatively broad; M3 relatively broad (see comparisons in account of the Cuban subspecies beyond); mesostyle of M1 and M2 and 2nd commissure and cingulum of M3 large; pelage yellowish to yellowish-orange.

Comparisons.—See p. 79 and under accounts of Lasiurus intermedius floridanus and the Cuban subspecies.

External measurements.—Three adult males from the Sierra de Tamaulipas in Tamaulipas: Total length, 146, 136, 142; length of tail-vertebrae, 69, 67, 70; length of hind foot, 11, 11, 11; length of ear from notch, 17, 16, 17; length of forearm (dry), 53.2, 51.8, 51.9. Corresponding measurements for two adult females from 1 mi. SW Catemaco, Veracruz: 149, 155; 64, 69; 11, 12; 17, 17; 51.8, 55.2. Weight in grams of the Tamaulipan specimens, respectively: 24, 21, 24. For cranial

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