This species, as is known, is active by day and by night. It occurs
mainly in grassy areas and most of the specimens examined were trapped
there. But, one mile east of La Pesca, specimens were taken on a beach
having sparse grass. _Neotoma micropus_ and _Spermophilus spilosoma_,
but no smaller rodents, were taken there. Also, many crabs were found
in the traps. Possibly only the relatively large rodents are able to
compete successfully with the crabs. The specimen from one kilometer
east of El Barretal was caught in a rat-trap set in front of small hole
in a fence of dead brush that surrounded a cornfield. The area outside
the fence supported mesquite and ebony trees (10-12 feet high) and the
ground was covered with cat claw. Six miles north and six miles west of
Altamira, the two young specimens were taken on a small grassy island
surrounded by mud.
According to natives, _Sigmodon_ injures corn and sugar cane. Probably
other species of rodents are responsible for some or all of such damage
since other kinds of rodents were taken in the same areas.
Dice (1937:245) reported females from the Sierra San Carlos that
carried 8 embryos of 18 mm., 5 x 33, 7 embryos very small, and 8 x 20.
Females were collected on July 22, 29, and 30.
=Sigmodon hispidus berlandieri= Baird
1855. _Sigmodon berlandieri_ Baird, Proc. Acad. Nat. Sci.
Philadelphia, 7:333, type from Rio Nazas, Coahuila.
1902. _Sigmodon hispidus berlandieri_, V. Bailey, Proc.
Biol. Soc. Washington, 15:106, June 2.
_Distribution in Tamaulipas._--From Jaumave and Llera to
north.
This subspecies is distinguished from _S. h. toltecus_ by larger size
and paler, grayish coloration.