Figure 7.14. Alston's Brown Mouse (Scotinomys teguina). Photograph by Richard K. LaVal.Slender Harvest Mouse
(Reithrodontomys gracilis)
The Slender Harvest Mouse is small (8—14 g) and pro-
duces a two-note high-pitched whistle. The call is
commonly heard in the forest and pastures at dusk
and after dark (Uyehara 1990, C. Langtimm, unpubl.
data). The species is extremely arboreal, spending a
large portion of its time climbing in plants of pastures
and the forest understory and in the crowns of canopy
trees (Langtimm 1992). They do not call readily in
captivity. Sonograms of calls I recorded from the
understory and in the canopy (22 m above the forest
floor) show that the dominant frequency of a note
ranges between 9 and 10.5 kHz. The second note im-
mediately follows the first and is slightly lower in
frequency. Single note calls are also commonly heard.
The duration of the entire two-note call ranges from
only 0.85 to 0.99 sec (C. Langtimm, unpubl. data). The
function of the call is unknown.
Reithrodontomys sp.This undescribed mouse species makes one-, two-,
and three-note calls. It is larger than the Slender Har-
vest Mouse (ca. 18 g) but similarly appears to be par-tially arboreal, based on the capture of two individu-
als in traps located 2—3 m above the forest floor onto
branches (C. Langtimm and F. Reid, unpubl. data).
The call is similar to that of the Slender Harvest
Mouse but differs in that the dominant frequency is
1 kHz lower and three-note calls are common; no more
than two successive notes have been heard for the
Slender Harvest Mouse (C. Langtimm and F. Reid,
unpubl. data). The call is similar to that described for
R. fulvescens in Louisiana by Svihla (1930): "a tiny,
clear high-pitched bugling sound." The occurrence of
long-distance vocalizations in two other species of
Reithrodontomys in Monteverde and the similarity
in the structure of their calls suggest that long-distance
auditory communication may be common in the
genus.Sumichrast's Vesper Rat
(Nyctomys sumichrasti)Sumichrast's Vesper Rat is the largest of the vocaliz-
ing mice in Monteverde (38-67 g). The species is ar-
boreal (Genoways and Jones 1972, Langtimm 1992).
It eats primarily fruits and seeds and is active at night.
Calls consisted of single chirps repeated at variable
time intervals. The peak frequency of a chirp (near 3.5237 Mammals