Microhabitat preferences and spatial distribution of the vesper rat (Nyctomys sumichrasti) in Colima, Mexico


The vesper rat (Nyctomys sumichrasti), a little-known arboreal rodent, was encountered during mark-recapture studies in Colima, Mexico, in January 2003-2007. We trapped on the Pacific coast at Playa de Oro (2003-2005) and in northern Colima (2006-2007). Each year five trap grids were established in heavily vegetated areas and typically run for 8 nights (100 trap stations per grid, each station with a ground trap and an arboreal trap elevated 1-2. m, 10×10 configuration with adjacent stations 10. m apart; 1,600 trap-nights per grid; 40,000 trap-nights total). Nyctomys sumichrasti occurs throughout most of Colima. On grids we captured 29 individuals a total of 41 times, with 90.2% of captures in arboreal traps and 69.0% of animals being adults. The sex ratio of adults was 1.22:1 (males:females), not statistically different from 1:1. Most adult females (77.8%) were pregnant or lactating. Mean mass was 41.3 and 38.6. g for males and females, respectively (P>0.05). Mean greatest distances traveled were longer for males (60.6. m) than females (20.2. m), with an overall mean of 40.4. m. One to six individuals were captured on 9 of 25 grids, with density estimates of 0.87-4.09/ha. We contrasted 14 environmental measures (most involving vegetation structure) for stations where N. sumichrasti was caught and not caught using logistic regression and nonparametric multiplicative regression, finding the species frequented sites flat to moderate in slope with considerable ground litter and relatively sparse high vegetation. In northern Colima, N. sumichrasti used areas with close trees, an open understory, and little grass. Other studies indicate the species sometimes occupies similar areas but with a relatively dense understory. © 2010 Deutsche Gesellschaft für Säugetierkunde.

Publication Title

Mammalian Biology