Reproductive strategies and natural history of the arboreal Neotropical vesper mouse, Nyctomys sumichrasti

The vesper mouse, Nyctomys sumichrasti (Rodentia: Cricetidae), a poorly known, arboreal, nocturnal, rodent found in Central America, has been considered rare, and limited information is available about its biology, especially reproduction. We obtained vesper mice from several sites in Costa Rica and prepared them as scientific specimens with standard external measurements and reproductive data recorded. We expanded our dataset by including specimens from museum collections. Vesper mice have 1:1 sex ratios throughout their range. They reproduce year-round and litters may occur in rapid succession. Testis size is positively correlated with body mass; however, we could not determine the onset of sperm production. The onset of reproduction for females, based on mass, is variable but most females are parous by 60 g. Litter size is small with a mode of two, and embryos are not evenly distributed across the uterine horns. Vesper mice exhibit striking morphological differences in terms of tooth-wear and pelage patterns across their range. Much work is needed to fully appreciate N. sumichrasti, its role in tropical habitats, and its reproductive biology.