More than half of the population of Colombia is settled in the Magdalena River basin, resulting in high deforestation rates due to productive activities and urbanisation. Within this scenario of forest loss and ecosystem degradation, it is imperative to record and monitor the biodiversity in order to decrease and mitigate the negative consequences of human activities on species and ecosystems. For six years, we assessed the mammal species richness, abundance and activity patterns in premontane forests of the Magdalena River basin in the Department of Caldas, Colombia. We also presented additional information on the geographical affinities of this fauna. We recorded 101 species, seven of them endemic to Colombia, with Chiroptera being the richest order, followed by Rodentia. Most of the species are common and not listed in threatened categories and only four are vulnerable and two endangered, according to the Red List of the IUCN and the Ministerio de Medio Ambiente y Desarrollo Sostenible of Colombia. The mammalian fauna of the study area is similar to that of other lowland localities in the Neotropics and different to the fauna in highland localities, including the nearby ones. Specifically, this fauna was most similar to that in lowland Tolima and the Caribbean Region of Colombia, Venezuela and Costa Rica; however, when we accounted only for bat fauna, it was more similar to the fauna in Caribbean and Pacific Regions of Colombia. To secure the long-term persistence of these species, we recommend maintenance of the current corridors, such as riparian forests and living fences and an increase in the forested area.

biodiversity, biogeography, Caldas, checklist, inventory, monitoring

The Magdalena River basin is located in northern South America in Colombia (Morrone 2014). This river has its origin in the Andes mountains (Colombian Massif) and flows northwards between the Central and Eastern Cordilleras throughout the Magdalena River Valley, emptying finally into the Caribbean Sea (Hermelin 2016). Biogeographically, this basin is classified as the Magdalena Province and belongs to the Pacific domain, sharing a taxa composition with nearby Provinces, such as Guajira, Chocó-Darién and Cauca (Hernández-Camacho et al. 1992; Kattan et al. 2004; Morrone 2014).

This Basin is of great economic relevance for the country because a large part of the Colombian population and their productive activities are settled there (IDEAM 2001). Such a level of economic development has produced a continuous pressure on natural resources, resulting in high rates of deforestation mainly at low to mid elevations (Armenteras et al. 2013). It is estimated that around 70% of Andean and 30% of lowland forests in Colombia have been lost (Etter et al. 2006a, b), especially in the Magdalena River basin (Etter and van Wyngaarden 2000). The current landscapes in this basin are very heterogeneous, where forests are represented mainly by fragments immersed in an agricultural matrix with different levels of connection through riparian forests and living fences (Etter et al. 2008). The remaining extensive areas of forests are mainly associated with the Andean highlands, natural parks and private civil reserves, as well as hydroelectric dams (Armenteras et al. 2003).

In this context of forest loss and fragmentation, it is important to monitor the biodiversity in order to prevent, mitigate, compensate or correct the negative effects of socio-economic activities on ecosystems (Schmeller et al. 2017). An important tool for this purpose is species inventories which result in checklists, natural history field data and spatiotemporal trends in species richness and abundance (Christoffersen 2010, Lees et al. 2014). The data obtained from the previous activities allow the construction and improvement of species distributional hypotheses (Elith et al. 2006) and to the identification of evidence-based important areas for conservation (Niemelä 2000).

In the Magdalena River and its tributaries, mammal inventories can be tracked back as far as the 19^th century (Mantilla-Meluk et al. 2014) and, during the last decades, checklists have been frequently published (e.g. Moreno-Bejarano and Álvarez-León 2003; Castaño and Corrales 2010; Garcés Retrepo et al. 2016; Solari et al. 2020). However, most published inventories and monitoring are based on one year or less sampling efforts and the local mammalian richness is generally underestimated. Here, we provide a checklist for mammals from premontane forests on the eastern slopes of the Central Cordillera in the Department of Caldas, Colombia, as a result of field data collection distributed over six years (2014–2019). We also provide some insights into the geographical affinities of this fauna and data on their activity patterns.

Premontane forests, located on the eastern slopes of the Central Andes below 1000 m in the Department of Caldas, sustain at least 101 species of mammals, mostly common species that are not listed as threatened. This number represented 19% of the mammalian richness in Colombia (528 species; Sociedad Colombiana de Mastozoología et al. 2020) and it is expected to increase with additional sampling efforts. Bats as the richest order and rodents as the second follow the same pattern found at the national scale (Solari et al. 2013).

We expected to find, according to the estimator Chao 1, at least nine species more if the sampling effort were increased. Checklists of mammals in localities in the Magdalena River basin report species that were not found in the study area, but their presence is highly probable, especially bats such as Myotis caucensis, M. albescens, Pteronotus parnellii, Trachops cirrhosus, some molossid species and nectarivorous bats, such as Hsunycteris thomasi and Lionycteris spurrelli (García-Herera et al. 2019; Solari et al. 2020). Some carnivorous mammals, such as Herpailurus yagouaroundi or Bassaricyon neblina, are also expected (Sánchez-Giraldo and Daza 2017; Gerstner et al. 2018). Besides increasing the sampling effort, it is important to focus it on habitats where rare species concentrate their activities. This was the case of the bat Eumops hansae, which was captured over the Manso River in a net set across the river, a method that was rarely used in this or other studies; the specimen captured by this method was the first reported for the country (Torres and Rojas 2020).

The mammalian fauna found in the study area is composed mostly of common species with wide geographic ranges; however, the presence of seven Colombian endemic small mammals with restricted geographic ranges associated with premontane and cloud forests in the Magdalena River basin emphasises the conservation value of premontane forests in the east of the Department of Caldas; indeed, this area had already been identified as a regional centre of mammalian endemisms (Castaño 2012). Since non-volant small mammals have low dispersal ability, local deforestation associated with agricultural activities can cause local population extinctions of these endemic species and restrict them to isolated forested areas (Castro and Fernandez 2004, Paise et al. 2020). This is especially true for the marsupial Marmosops chucha, the rodent Rhipidomys caucensis and the primate Saguinus leucopus that carry out their activities above the ground in the lower, middle and upper forest strata (pers. obs., Poveda and Sánchez-Palomino 2004). To ensure the survival in the long term for these endemic species, it is imperative to increase the connectivity of forest fragments and maintain the already existing corridors such as riparian forests and living fences (Zimbres et al. 2017).

Most species in the study area are not listed in lower threatened categories (LC or NT); however, 10 species showed a globally-decreasing population trend. This pattern is part of a world phenomenon known as defaunation, which means the progressive loss of animal populations caused mainly by habitat loss (Dirzo et al. 2014). Interestingly, eight of the eleven species with decreasing populations, according to the Red List, feed on other animals (i.e. animalivorous), despite belonging to different taxonomic groups, such as bats (Vampyrum spectrum), carnivores (Leopardus pardalis or Lontra longicaudis), marsupials (Chironectes minimus) and rodents (Ichthyomys hydrobates). Animalivory is a functional trait of species that has been associated with increased vulnerability to habitat loss and fragmentation because of their lower population densities and slow life histories (Cardillo et al. 2004; Minin et al. 2016).

Since ambient temperature is an important determinant of the distribution of many animals (Bozinovic et al. 2011) and the inter-Andean valley, through which the Magdalena River flows, opens in the north, the faunistic similarity between the study area and the warm Caribbean Region in Colombia, Costa Rica and Venezuela was not surprising. This inter-Andean valley could be defined as a “warm corridor” for mammalian species adapted to these warm environmental conditions. The warm lowlands similarity was also supported by the fact that mammalian fauna in the Central Cordillera below 1000 m (both the study area and Tolima) and the Caribbean localities are more related to the warm lowlands of the Amazon and Guiana Shield, than they are to closer regions like West and Central Cordilleras above 2000 m, which have lower temperatures. Our analysis restricted to bats also points to this relationship and adds to the group of “lowland fauna”, the bat fauna of the Pacific Region below 1000 metres.

Similar relationships between lowland areas have also been described for birds (Kattan et al. 2004; Cadena et al. 2016). For these flying vertebrates, it has been hypothesised that relationships amongst lowland areas in northern South America were mediated by dispersal events (Cadena et al. 2016). One hypothesis is that this dispersion occurred throughout the north in the Caribbean lowlands (Haffer 1967a, b). Another hypothesis proposes that this occurred through passes in the Andes, such as the Táchira depression in northern East Cordillera or Andalucía pass and Suaza-Pescado valleys at the south of this same Cordillera (Cadena et al. 2016). Possible examples of this historical dispersion in mammals may be the bats Artibeus planirostris and Sphaeronycteris toxophyllum which are distributed in the lowlands east of the Andes, but also extend their distribution into the Magdalena River basin and Caribbean Region (Solari et al. 2013; García-Herrera et al. 2018). At least in the case of A. planirostris, molecular evidence suggests dispersion from the Guiana Shield and Venezuela into the Lesser Antilles and northern South America (Larsen et al. 2007).

Most analysed mammal species were active during the night, beginning at dusk and finishing at sunrise. This is the typical mammalian pattern; and, as it is currently understood, this was the ancestral behaviour of the placental mammalian ancestor (Gerkema et al. 2013); thus, activity during the day, as shown by some species, may be considered a derived behavioural trait. In general, the activity patterns of many Neotropical mammals of medium and large size are well-known (e.g. Blake et al. 2012; Ramírez-Mejía and Sánchez 2016; Huck et al. 2017); however, the small mammals activity patterns are under-studied (Ferreira and Vieira 2016). Thus, the data, shown in this study on the activity patterns of the endemic spiny rat Proechimys chrysaeolus, are an important contribution to this topic. The activity pattern of P. chrysaeolus was similar to the patterns found in other species of Proechimys in the Brazilian Amazon (Pratas-Santiago et al. 2016).

Premontane forests of the Magdalena River basin in eastern Caldas harbour a rich mammalian fauna, consisting mostly of common species of lowland origins. However, these forests are of high conservation value because they host at least seven endemic species and five Endangered or Vulnerable species. To secure the long-term persistence of these species, we recommend maintaining the current corridors, such as riparian forests and living fences and increasing the forested area.

ISAGEN and the Universidad de Caldas financed this study (agreement 33/45). We thank Beatriz Edilma Toro, John Harold Castaño and Thomas Defler for valuable comments to this manuscript and Mary Luz Bedoya for administrative and logistical support. We are grateful to editors and two anonymous reviewers who greatly improved this manuscript.