Speciation and Evolution of the Pygmy Mice, Genus Baiomys Part 5

_Behavior._--Little is recorded concerning the behavior of this species.

David and Russell (_op. cit._:76) found that of small mammals _B.

musculus_ was the first to appear at night. I caught mice of this species by hand in the afternoon in Puebla. They seemed to be active from noon until dark. Albert Alcorn wrote in his field notes that specimens were taken near noon at a place 9 mi. NNW Esteli, Nicaragua.

My impression is that _musculus_ is diurnal to crepuscular.

_Enemies and food._--Owl pellets (thought to be those of a barn owl, _Tyto alba_) from within the geographic range of _B. musculus_, from 6 mi. SW Izucar de Matemores, yielded mandibular tooth-rows belonging to _musculus_. Presumably, most of the carnivorous mammals and raptorial birds within the range of the southern pygmy mouse could be listed as enemies. Diurnal to crepuscular habits of this mouse may protect it from some of the nocturnal carnivorous mammals and raptorial birds.

Food of the southern pygmy mouse includes nuts, bark, gra.s.s seeds, and leaves. Dalquest (MS) writes that bits of banana proved to be useful bait in trapping these mice in Veracruz.

_Reproduction._--Notations concerning lactation and embryos on specimen labels of females suggest that the southern pygmy mouse breeds in all months. I have records of pregnant or lactating females in every month, save January, April, May, and June. The average of 26 counts of embryos or young per litter is 2.92 (1-4).

=Baiomys musculus brunneus= (J. A. Allen and Chapman)

_Peromyscus musculus brunneus_ J. A. Allen and Chapman, Bull. Amer.

Mus. Nat. Hist., 9:203, June 16, 1897; Elliott, Field Columb. Mus.

Publ., 105(4):136, July 1, 1905; Elliott, Field Columb. Mus. Publ., 115(8):203, 1907; Osgood, N. Amer. Fauna, 28:259, April 17, 1909.

_Baiomys musculus brunneus_, Miller, Bull. U. S. Nat. Mus., 79:137, December 31, 1912; Miller, Bull. U. S. Nat. Mus., 128:318, April 29, 1924; Ellerman, The Families and Genera of Living Rodents, 2:402, March 21, 1941; Goldman, Smith. Miscl. Coll., 115:437, July 31, 1951; Goodwin, Bull. Amer. Mus. Nat. Hist., 102:318, August 31, 1953; Miller and Kellogg, Bull. U. S. Nat. Mus., 205:512, March 3, 1955; Booth, Walla Walla Publs., Dept. Biol. Sci., 20:15, July 10, 1957; Hall and Kelson, The Mammals of North America, 2:661, March 31, 1959 (part).

[_Peromyscus musculus_] _brunneus_, Elliott, Field Columb. Mus.

Publ., 95(4): 176, 1904.

_Peromyscus musculus_ [_musculus_], Osgood, N. Amer. Fauna, 28:258, April 17, 1909 (part).

_Baiomys musculus musculus_, Davis, Jour. Mamm., 25:394, December 12, 1944 (part); Goldman, Smith Miscl. Coll., 115:437, July 31, 1951; Hooper, Jour. Mamm., 33:97, February 18, 1952 (part); Hall and Kelson, The Mammals of North America, 2:661, March 31, 1959 (part).

_B._ [_aiomys_] _m._ [_usculus_] _brunneus_, Hooper, Jour. Mamm., 33:96, February 18, 1952.

_Baiomys taylori_, Hooper, Jour. Mamm., 33:97, February 18, 1952 (part).

_Type._--Adult female, skin and skull; No. 12535/10845 American Museum of Natural History; Jalapa, Veracruz, Republic of Mexico; obtained on April 13, 1897, by F. M. Chapman, original number 1203.

_Range._--Central Veracruz, coastal plains and eastern slopes of the plateau of Central Mexico, see Figure 10. Zonal range: Upper Tropical Life-zone (Lowery and Dalquest, 1951:537), parts of the Veracruz and eastern Transverse Volcanic biotic provinces of Goldman and Moore (1945:349). Occurs from near sea level at Boca del Rio, Veracruz, up to 5500 feet 3 km. SE Orizaba.

_Diagnosis._--Size medium to large for the species; ground color of dorsum of paratypes near Olive Brown; darkest of specimens of this subspecies examined (from Potrero Viejo, Veracruz) between Prouts Brown and Mummy Brown; distal two-thirds of guard hairs of dorsum black, proximal third dark gray to sooty; hairs of dorsum black-tipped having subterminal band of Ochraceous-Tawny; sides paler (less of dark brown) than dorsum; venter Deep Olive Buff to clay color, individual hairs pale olive buff at tips, dark gray basally; region of throat and chin sooty gray; ventralmost vibrissae white to base, other vibrissae black to base; ears dark brown, spa.r.s.ely haired; forefeet and hind feet flesh-colored in palest specimens, sooty in darkest; tail pale brown, slightly paler below than above; presphenoid only slightly constricted towards midline; average and extreme external and cranial measurements of 10 adults from Cerro Gordo, Veracruz, are as follows: total length, 118.9 (112-127); length of tail vertebrae, 45.1 (42-50); length of body, 74.0 (69-78); length of hind foot, 16.0 (16); length of ear from notch, 12.8 (12-13); occipitonasal length, 19.5 (19.0-20.0); zygomatic breadth, 10.3 (10.0-10.8); postpalatal length, 7.1 (6.7-7.5); least interorbital breadth, 3.9 (3.7-4.0); length of incisive foramina, 4.4 (4.1-4.6); length of rostrum, 6.9 (6.5-7.2); breadth of braincase, 9.5 (9.2-9.7); depth of cranium, 7.1 (7.1-7.4); alveolar length of maxillary tooth-row, 3.3 (3.2-3.3); for photographs of skull, see Plate 1_a_, and Plate 3_a_.

_Comparisons._--For comparisons with _B. m. nigrescens_, see account of that subspecies. From _B. m. pallidus_, _B. m. brunneus_ differs in: dorsal, lateral, and facial coloration deeper reddish brown, more melanins present; venter darker; buff gray rather than whitish buff to gray as in paratypical series; vibrissae black rather than brownish to white; tail sooty, less flesh-colored; forefeet and hind feet averaging slightly grayer; most external and cranial dimensions averaging slightly larger; nasals less attenuated; presphenoid less hour-gla.s.s shaped, sides more nearly straight.

From _B. m. infernatis_, _B. m. brunneus_ differs in: side of face and neck deep reddish-brown rather than yellowish-gray (the differences in dorsal colorations are greater between _brunneus_ and _infernatis_ than between _brunneus_ and _pallidus_); venter darker buff-gray; tail brownish rather than flesh-colored; forefeet and hind feet average slightly grayer; most external dimensions averaging slightly larger; cranial dimensions nearly the same except length of incisive foramina, which is smaller; presphenoid differs in much the same way as from pallidus.

_Remarks_.--Specimens from Chichicaxtle, Puente Nacional, 3 km. W Boca del Rio, 1 km. E. Mecayucan, and Rio Blanco (20 km. WNW Piedras Negras), are all paler than the paratypical series and other specimens from within the a.s.signed range of _B. m. brunneus_. All these specimens from the coastal plain average considerably paler than those from the front range and slopes of the mountains. Specimens from Puente Nacional are intermediate in color between paler, grayish brown, specimens from the coastal plains and the darker, brown, specimens from the mountains. When Allen and Chapman (1897:203) described _brunneus_, they did so on the basis of the darker brown mice from the higher alt.i.tudes. The name, _brunneus_, _sensu stricto_, could be restricted to those mice from the higher alt.i.tudes of central Veracruz. However, when the mice of intermediate color from Puente Nacional are considered, it seems best to include the material from the coastal plain with _brunneus_. Crania from the higher alt.i.tudes are slightly larger than, but not significantly different from, crania of specimens from the coastal plains. Specimens examined from the coastal plains resemble the darker series of _B. m.

pallidus_ to the west in central Mexico. But there is no evidence of gene flow between the paler coastal specimens and _B. m. pallidus_ to the west. In fact, these paler brown mice on the coastal plain grade in color into the darker brown mice from the mountains. The paler mice from the coast may be an incipient subspecies.

The type and paratypes seem to have faded somewhat since they were described by Allen and Chapman (_loc. cit._) and by Osgood (1909:259).

However, the color of the paratypes and other specimens herein a.s.signed is the feature most useful for distinguishing _brunneus_ from all other subspecies of _B. musculus_.

_Specimens examined._--Total 187 all from VERACRUZ, Republic of Mexico, and distributed as follows: type locality, 4400 ft., 16[1] (including the type), 6[2], 1[3]; _Cerro Gordo_, 1500 ft., 19; _Teocelo_ [= _Texolo_], 4500 ft., 1; _2 mi. NW Plan del Rio_, 1000 ft., 14[4]; _Plan del Rio_, 1000 ft., 2[5]; _Carrizal_, 4[2]; Chichicaxtle, 3[2]; _Puente Nacional_, 500 ft., 1[5], 2; _Santa Maria, near Mirador_, 1800 ft., 10[2]; Boca del Rio, 10 ft., 1[5], 8; _Cordoba_ [= _Cordova_], 14[1]; _4 km. WNW Fortin_, 4; _Rio Atoyac, 8 km. NW Potrero_, 1; _2 km. N.

Paraje Nuevo_, 1700 ft., 9; _El Xuchil_, _1 mi. W. Paraje Nuevo_, 6[6]; Potrero Viejo, 1700 ft. 15; _Cautlapan_ [= _Ixtaczequitlan_], 4000 ft., 16; _Micayucan_, 1; 3 km. SE Orizaba, 5500 ft., 3; Rio Blanco, 20 km.

WNW Piedras Negras, 400 ft, 7; _29 km. SE Cordoba, Presidio_, 15[4]; _3 km. N Presidio_, 1500 ft., 2; Presidio, 600 meters, 6[3].

_Marginal records._--VERACRUZ: type locality; Chichicaxtle; Boca del Rio, 10 ft.; Rio Blanco, 20 km. WNW Piedras Negras, 400 ft; Presidio; 3 km. SE Orizaba, 5500 ft.

[1] American Museum of Natural History.

[2] U. S. Nat. Museum (Biol. Surv. Coll.).

[3] Chicago Natural History Museum.

[4] Univ. Michigan, Museum of Zoology.

[5] Texas A & M, Coop. Wildlife Res. Coll.

[6] Univ. Illinois, Mus. Nat. History.

=Baiomys musculus grisescens= Goldman

_Baiomys musculus griesescens_ Goldman, Proc. Biol. Soc. Washington, 45:121, July 30, 1932; Ellerman, The Families and Genera of Living Rodents, 2:402, March 21, 1941; Poole and Schantz, Bull. U. S. Nat.

Mus., 178:259, March 6, 1942; Goodwin, Bull. Amer. Mus. Nat. Hist., 79(2):160-161, May 29, 1942 (part); Miller and Kellogg, Bull. U. S.

Nat. Mus., 205:513, March 3, 1955 (part); Felten, Senck. Biol., 39:136, August 30, 1958; Packard, Univ. Kansas Publs., Mus. Nat.

Hist., 9:401, December 19, 1958; Hall and Kelson, The Mammals of North America, 2:661, March 31, 1959 (part).

_Type._--Adult female, skin and skull; No. 257083 U. S. Nat. Mus. (Biol.

Surv. Coll.); Comayabuela [= Comayaguela] just south of Tegucigalpa, 3100 feet, Honduras; obtained on March 6, 1932, by C. F. Underwood, original number 838.

_Range._--Central to south-central Guatemala, east to south-central Honduras. Zonal range: Lower parts of the Merendon Biotic Province of Smith (1949:235). Occurs from 3200 feet at a place 1/2 mi. N and 1 mi. W Salama, Guatemala, up to approximately 4500 feet at Monte Redondo, Guatemala.

_Diagnosis._--Size medium to small for the species; general ground color of dorsum between Olive Brown and Buffy Brown; distal fourth of individual guard hairs of dorsum black-tipped, proximal three-fourths gray, underfur black-tipped with subterminal band of Vinaceous-Buff, gray basally; facial region below eye Olive-Buff to Deep Olive-Buff; regions of flanks without black-tipped guard hairs, therefore, appearing paler brownish-buff than dorsum; venter Pale Olive-Buff to whitish in midline, hairs there white to base, laterally grayish basally; hairs in region of throat and chin resemble those of underparts; forefeet and hind feet flesh-colored with grayish suffusion; ears dusky brown; tail almost unicolored, slightly darker brown above than below; coronoid process less acutely falcate than in other subspecies; zygoma bowed.

Average and extreme external and cranial measurements of 14 adults from La Piedra de Jesus Sabana Grande, Honduras, are as follows: Total length, 110.7 (100-123); length of tail vertebrae, 44.0 (32-55); length of body, 66.7 (60-70); length of hind foot, 14.1 (12-15); length of ear from notch, 11.8 (10-13); occipitonasal length, 19.3 (18.9-19.8); zygomatic breadth, 10.1 (9.8-10.4); postpalatal length, 6.8 (6.2-7.3); least interorbital breadth, 3.9 (3.8-4.1); length of incisive foramina, 4.3 (4.0-4.5); length of rostrum, 6.9 (6.6-7.2); breadth of braincase, 9.6 (9.2-10.1); depth of cranium, 7.0 (6.8-7.3); alveolar length of maxillary tooth-row, 3.2 (3.0-3.4); for photographs of skull, see Plate 1_b_, and Plate 3_b_.

_Comparisons._--For comparisons with _B. m. pullus_ and _B. m.

handleyi_, see accounts of those subspecies. From _B. m. nigrescens_, _B. m. grisescens_ differs in: dorsum less blackish (dark brown to buffy); face buffy below eye rather than brownish-black; venter buffy to whitish in midline, not sooty gray; forefeet and hind feet flesh-colored with gray overtones, not dusky to sooty; zygoma bowed, sides less parallel; braincase and bony palate slightly broader.

_Remarks._--Goodwin (1942:160) mentioned that a specimen from the type locality of _grisescens_ was as dark as specimens of _B. m. nigrescens_ from Guatemala. However, all specimens from Guatemala, other than those from Sacapulas, were referred by Goodwin (1934:40) to _B. m.

nigrescens_. My studies reveal a grayish-brown population in central Honduras near to and including the type locality. This population appears to grade into a slightly paler, particularly as concerns color of hind foot and tail, group of Guatemalan mice from 1 mi. S Rabinal, from 1/2 mi. N, 1 mi. E Salama, and from Lake Atescatempa. Specimens from western Guatemala at Nenton and Jacaltenango, on the other hand, are darker brownish-black, more nearly like the paratypical series of _nigrescens_ from the Valley of Comitan, Chiapas, Republic of Mexico.

This darker brownish-black color of the back persists in specimens from southern Guatemala and El Salvador (see specimens examined of _B. m.

nigrescens_ for localities), and they are best referred to _nigrescens_.

_B. m. grisescens_, in color and certain cranial characters, therefore, seems to grade into two different subspecies: (1) _B. m. handleyi_, pale mice in the Rio Negro valley in central Guatemala, and (2) _B. m.

nigrescens_, dark mice from southern Guatemala, and parts of El Salvador.

Felten (1958:136) referred all _B. musculus_ from El Salvador to _B. m.

grisescens_. Although I have not examined the specimens reported on by Felten (_loc. cit._), I have examined specimens from Lake Atescatempa, Guatemala (which I refer to _grisescens_), not too distant from Cerro Blanco, and Finca Las Canarias, Department of Ahuachapan, and Laguna de Guija, Department of Santa Ana (localities listed by Felten). It would seem that specimens from these localities might indeed be _grisescens_.

However, specimens that I examined from 1 mi. S Los Planes, and 1 mi. NW San Salvador were considerably darker than paratypes of _grisescens_ and were nearly intermediate in color between _nigrescens_ and _pullus_. I refer the specimens from 1 mi. NW San Salvador, and 1 mi. S Los Planes to _nigrescens_ rather than to _grisescens_.

There is no positive evidence that _B. m. grisescens_ intergrades with _B. m. pullus_ to the south in Nicaragua. But, there is a suggestion that intergradation occurs between these subspecies in a series of 76 skins from La Piedra de Jesus Sabana Grande, Honduras, referable to _grisescens_. A total of 16 of 76 skins from this locality (21 per cent) possess the mid-ventral white stripe found in 18 of 20 skins (90 per cent), from the type locality of _pullus_ in Nicaragua. Further collection in areas between central Honduras and western Nicaragua may yield specimens of _B. musculus_ that are intermediate in characters between _grisescens_ and _pullus_.

_Specimens examined._--Total 149, distributed as follows: GUATEMALA: 1 mi. S Rabinal, 3450 ft., 14; 1/2 mi. N, 1 mi. E Salama, 3200 ft., 10; Lake Atescatempa, 10[7]. HONDURAS: Cementario, Gracias, 1[8]; Monte Redondo, 1[8]; El Caliche, Cedros, 1[8]; _La Flor Archaga_, 2[8], 1[9]; Hatillo, 1[8]; _type locality_, 7[8], 6[7] (including the type), 3[9]; _El Zapote_, _Sabana Grande_, 4[8]; La Piedra de Jesus Sabana Grande, 76[8]; _Cerro de las Cuches Sabana Grande_, 5.

_Marginal records._--GUATEMALA: 1/2 mi. N, 1 mi. E Salama, 3200 ft.