A new locality in Paraguay for the Black-tailed Marmoset , Mico melanurus ( Geoffroy Saint-Hilaire , 1812 ) ( Primates , Callitrichidae )

Mico melanurus is an endangered primate in Paraguay, with most Paraguayan records in the vicinity of Agua Dulce (Defensores del Chaco National Park). We report the first well-documented locality outside of the Agua Dulce/ Linea 1 transect, representing the most northeastern record in Paraguay, as well as a new habitat for the species, transitional Pantanal-Cerrado. This note demonstrates the importance of monitoring areas which have been insufficiently studied for conservation purposes.

The smallest species, M. melanurus, is restricted to the extreme northeastern Chaco (Stallings & Mittermeier 1983).This species was formerly considered a subspecies of the Silvery Marmoset (M.argentatus) until elevated to full species status by de Vivo (1991).
The majority of sightings of M. melanurus in Paraguay have been in the vicinity of Agua Dulce (Defensores del Chaco National Park, Departamento de Alto Paraguay), between the ranger station and a swath of forest extending 3 km to the east (Table 1).The frequency of these sightings were largely bimodal, taking place during the early 1980s (Stallings & Mittermeier 1983), and again between 2007 and 2010 (Smith 2010, Giordano, pers. comm.).
While M. melanurus has been reported by interviewees further north and east of Agua Dulce (Brooks 1996), direct encounters have been documented at only a couple of localities.Stallings & Mittermeier (1983) observed M. melanurus east of Agua Dulce along Linea 1 (the same latitude as Agua Dulce, 20° S) at km 30 and 48, and up to 14 km south of km 48 (Fig. 1).During primate surveys in the northern Chaco in July 1990, Brooks (1996) only accounted for the 2 medium-sized species (C.pallescens and A. azarae) but not M. melanurus, although the area covered was west of Agua Dulce where it had not been recorded.
Herein we report a new record of M. melanurus in Paraguay well east and north of Agua Dulce, which also represents a new habitat recorded for this endangered Paraguayan primate (SEAM 2006).We briefly address the results in light of current habitat threats in the region, as land use changes are rapidly affecting Paraguayan wilderness before we have a firm understanding of what is being lost.
Current distribution of M. melanurus within and near Paraguay (Fig. 1, Table 1) was documented through literature review, and perusing museum database records for American Museum of Natural History (AMNH), Field Museum (FMNH), National Museum of Natural History (NMNH), University of Michigan Museum of Zoology (UMMZ) and VertNet (databases accessed 25 July 2016).These localities were compared to the site of the observation reported below On 20 July of 2016, HCB, LRN and DB were driving south on Linea 28 in a pickup truck at 60-70 km/hr, ca.20 km west of Mbarigui (Departamento de Alto Chaco, Paraguay; 19°47ʹ38.95ʺS, 058°48ʹ07.73ʺW).At 09:15 hr a group of 3 M. melanurus was observed running towards the road quadrupedally from the right side to cross to a large tree on the left.As the vehicle approached rapidly the marmosets split off (2 crossed the road to the left of vehicle, 1 remained on the right).The vehicle was immediately stopped and the observers got out to search the area, whereupon 2 additional marmosets were spotted 4 m off the ground in a tall tree (ca. 10 m high) to the left.The marmoset troop quickly climbed higher into a stand of Peltophorum dubium trees, where one of the individuals remained long enough to be observed for 15 min.(Fig. 2), before it also fled deeper into the forest to join the rest of the troop.
The habitat was transitional Pantanal-Cerrado (Mereles et al. 2013).The dirt road was 4 m wide, flanked by a 4 m wide swath of short grasses (≤ 5-7 cm high) on both sides of the road, which transitioned into taller savannah (≤ 1.7 m high) that was ca. 8 and 10 m wide on the left and right side, respectively.Typical Cerrado woodland was on the right side of this ca.30 m gap, and taller forest (10-12 m high) was on the left.Cerrado is comprised of a mixture of open vegetation with isolated trees and island forest (Mereles et al. 2013).As the vehicle was traveling between study sites, no other species of primates were recorded.
With Paraguay's arboreal mammalian fauna relatively depau-perate compared to more tropical areas closer to the equator, it is difficult to confuse M. melanurus with other species.The pelage and size of the primates observed (Fig. 2) clearly matched that of M. melanurus, with the upper torso being silvery-gray, becoming darker towards distal extremities of appendages, with a dark face, legs and tail; hip stripes; unpigmented nose and ears without tufts (de Vivo 1991).These characteristics matched museum specimens examined at NMNH by DMB, as well as photographs in Stallings (1989) and Smith (2010).This record is noteworthy, as it is the first well-documented locality for M. melanurus outside of the Agua Dulce/Linea 1 transect in Paraguay (23 km north, and 52 km east).A specimen at the National Musuem of Natural History (NMNH 3353) was collected by T.J. Page purportedly along the "Paraguay River" in 1852 (Table 1, Fig. 3).It is possible that this specimen was actually collected along the Paraguay River, but during that era it was common to create multiple tags for a base camp, the locality of which was assigned to all specimens, regardless of where they were collected.As T.J. Page did not provide the precise collection locality for this sample, it is impossible to  determine if the specimen was from the Agua Dulce/Linea 1 transect, or transitional Pantanal/Cerrado region.Stallings & Mittermeier (1983) reported that M. melanurus is restricted to Dry Chaco forest having a canopy that is mostly 5-10 m high along Linea 1 and 20-25 m high at localities south of Linea 1 where some emergent trees reach 30 m in height.The new locality is transitional habitat between Pantanal and Cerrado (Mereles et al. 2013).While M. melanurus has been reported to occur in other habitats, including near the study area in eastern Bolivia (Brooks et al. 2002), this is the first time it has been recorded in transitional Pantanal-Cerrado vegetation in Paraguay.There was a gap of ca. 30 m between forest patches, dictating the marmosets travel quadrupedally on the ground.Crossing wide gaps on the ground has been inferred in at least 1 other case for a Paraguayan primate (Giordano & Ballard 2010).
This region harbors other rare species as well.For example, a flock of 3 Red-and-green Macaws (Ara chloroptera) were recorded in the vicinity on the same day as the marmoset (HCB, LRN and DB unpubl.data).Additionally, this new marmoset record demonstrates the importance of monitoring areas which have been insufficiently studied.This area is located within a region of rapid land use changes which affect the area, particularly the Gran Chaco ecoregion (Hansen et al. 2013, Yanosky 2013).This transitional area is characterized by escalating deforestation patterns from pristine forests to grazing lands for livestock production (Hansen et al. 2013, Caballero et al. 2014, Pizzurno et al. 2014).Government plans and regional prioritization indicate the area will soon be transformed with new roads and other infrastructure.The observation herein provides information for decision making, in terms of mitigating loss of natural habitat and pertinent planning for compensation measures (Cardozo et al. 2013).
Figure 1.Map depicting known localities of Mico melanurus (squares) and the new locality (star).Protected areas include (A) Defensores del Chaco National Park, (B) Chovoreca National Park, and (C) Río Negro National Park.