Small mammals from the Seasonally Dry Tropical Forests of the Huallaga river basin and new records for San Martín department, Peru Dennisse Ruelas 1, 2* , Víctor Pacheco 1, 2 1 Museo de Historia Natural, Universidad Nacional Mayor de San Marcos, Lima, Peru • DR: druelasp@unmsm.edu.pe https://orcid.org/0000- 0002-3793-8639 • VP: vpachecot@unmsm.edu.pe https://orcid.org/0000-0002-1005-135X 2 Instituto de Ciencias Biológicas “Antonio Raimondi”, Facultad de Ciencias Biológicas, Universidad Nacional Mayor de San Marcos, Lima, Peru. * Corresponding author Abstract The Seasonally Dry Tropical Forests in Peru are well known for their bird and plant diversity and endemicity, but little is known about the diversity of small mammals. We report the diversity of small volant and non-volant mammals from the Seasonally Dry Tropical Forests of the Huallaga river basin in the San Martín Department, working on both sides of the river, making a sampling efort of 3060 traps-night for non-volant and 104 mist nets-night for volant mammals. We recorded 29 species, including fve marsupials, three rodents, and 21 bats. Among the bats, phyllostomids were the most diverse group with 16 species. Short-tailed Spiny-rat, Proechimys brevicauda (Günther, 1877) and Seba’s Short- tailed Bat, Carollia perspicillata (Linnaeus, 1758), featured the highest relative abundance. In addition, we report the frst records for the San Martín Department of Peropteryx macrotis (Wagner, 1843), Saccopteryx bilineata (Temminck, 1838), Lonchorhina aurita Tomes, 1863, Vampyriscus bidens (Dobson, 1878), and Myotis simus Thomas, 1901. The species richness and diversity indices indicate the study site has a high diversity value; however, fragmentation and rapid changes in land-use are the main threats faced by the biodiversity of these dry forests. Keywords Chiroptera, Didelphimorphia, fragmentation, Neotropics, Rodentia Academic editor: William Tavares | Received 19 December 2020 | Accepted 20 May 2021 | Published 7 June 2021 Citation: Ruelas D, Pacheco V (2021) Small mammals from the Seasonally Dry Tropical Forests of the Huallaga river basin and new records for San Martín department, Peru. Check List 17 (3): 877–894. https://doi.org/10.15560/17.3.877 Introduction Seasonally Dry Tropical Forests (SDTF) are character- ized by pronounced seasonality, annual rainfall less than 1600 mm, receiving about 80% of the rains during the wet season, resulting in several drought months during the dry season, which can last fve or six months (Pen- nington et al. 2000; Murphy and Lugo 1995; Maass and Burgos 2011). These forests have a smaller stat- ure and smaller basal areas than humid tropical forests (Pennington et al. 2000; Murphy and Lugo 1995). They range from Mexico to northern Argentina and southeast- ern Brazil, representing 22% of the forested area of South America (Murphy and Lugo 1986; Olson et al. 2001); but having a fragmented distribution with areas of diferent sizes (Espinosa et al. 2012). SDTF are foristic and structurally more complex than the rainforests (Murphy and Lugo 1986), although Check List 17 (3): 877–894 https://doi.org/10.15560/17.3.877 © The authors. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. ANNOTATED LIST OF SPECIES