SHORT COMMUNICATIONS ORNITOLOGIA NEOTROPICAL 14: 269–273, 2003 © The Neotropical Ornithological Society A SURVEY OF PERUVIAN TORRENT DUCKS (MERGANETTA ARMATA LEUCOGENIS) ON TWO RIVERS IN PERU Nancy L. Staus1 & Eugene F. Weast2 1Conservation Biology Institute, 260 SW Madison Avenue, Suite 106, Corvallis, OR 97333, USA. E-mail: [email protected] 2991 NW Sycamore Avenue, Corvallis, OR 97330, USA. Reconocimiento del Pato Correntino Peruano (Merganetta armata leucogenis) en dos ríos del Perú. Key words: Merganetta armata leucogenis, Peru, Peruvian Torrent Duck, survey. INTRODUCTION thus for directing conservation management of the species. The Torrent Duck (Merganetta armata) occu- We conducted surveys for Peruvian Tor- pies a large geographic range in the Andean rent Ducks on portions of two rivers in two highlands of South America, extending from major drainage systems in northern and Venezuela down to southern Chile (Callaghan southern Peru. Our objectives were to (1) 1998). One of only four species of anatid river locate river stretches that are used by Peru- specialists that exhibit year-round territoriality vian Torrent Ducks as potential sites for and long term pair bonds (Elridge 1986), the future study; and (2) establish new baseline Torrent Duck is ecologically limited to torren- numbers for monitoring population trends in tial mountain streams at elevations generally the future. greater than 1500 m (Johnsgard 1966). Torrent Ducks in the subspecies Mer- STUDY AREA ganetta armata leucogenis are found throughout Peru, Bolivia and Ecuador and are considered There are three major drainage systems in vulnerable by the Threatened Waterfowl Spe- Peru. To the west of the Andes, rivers drain to cialist Group (in prep.). Due to the birds’ the Pacific Ocean, to the east of the Andes scattered distribution and secretive manner, they drain to the Amazon river (which drains systematic population surveys are lacking and to the Atlantic Ocean), and rivers in the the Torrent Duck remains one of the least southern part of the Andes drain to Lake Titi- known species in the family Anatidae. Base- caca. We chose to survey rivers in two of line information about population density these drainage systems by their ease of access, and distribution is vital for successful detec- suitability for Torrent Ducks, and proximity tion of changes in population over time, and to areas that have been previously surveyed. 269 STAUS & WEAST FIG. 1. Map of Peru showing locations of Peruvian Torrent Duck surveys on the (a) Quebrada Santa Cruz, and (b) Urubamba River. Quebrada Santa Cruz. This river is a tributary river that runs through the Parque Nacional of the Río Santa that originates high in the Huascarán (Huascarán National Park) that Cordillera Blanca in northern Peru and drains was protected from many forms of human into the Río Santa about 70 km downstream disturbance such as dams and hydroelectric from Huaraz, and eventually into the Pacific plants, although livestock grazing was com- Ocean (Fig. 1a). We surveyed a portion of the mon. The portion of the river we surveyed 270 SHORT COMMUNICATIONS ranged in elevation from 4200 m to 3200 m. Urubamba River over a period of three days; Although it is protected in a National Park, three km downstream of Aguas Calientes and large portions of this river are subjected to four km upstream. On the Quebrada Santa livestock grazing, and the first ten km of the Cruz, we surveyed approximately thirteen km river surveyed (4200 m to 3800 m) were bar- over a three day period. This river became ren of streamside vegetation due to grazing by quite difficult to survey as the banks became horses, cows, and burros. In addition, much steep and major landslides had destroyed the of the river flowed at low gradients and may original trail that closely followed the river. not have been swift enough to support an ample food supply for the birds. RESULTS The Urubamba River. This river is located in Quebrada Santa Cruz. We found no sign of Tor- southwestern Peru and is a tributary of rent Ducks in the first ten km of the river, the Amazon River (Fig. 1b). The Urubamba even where the instream habitat seemed suit- begins high in the southern Peruvian able (e.g., fast flowing water, ample riffles). In Andes and flows northwest past Cuzco, the final three km that we were able to survey, through the Sacred Valley, winds around the banks became steeper thus deterring live- Machu Picchu, and finally joins the Tambo stock, and the streamside vegetation was River to drain into the Ucayali, and eventually thick. However, the only ducks we observed the Amazon River. The Urubamba is subject were two males who were jointly defending a to human disturbance in the form of agricul- very large territory that was at least one km in tural runoff and hydroelectric dams. There length. The males behaved like a mated pair, was an hydroelectric dam on the 7-km stretch feeding together and perching on the same of river that we surveyed. We conducted our boulder. They flew approximately one km survey out of Aguas Calientes, a small town downstream together when we disturbed located at approximately 2000 m elevation at them and were observed at their new location the base of Machu Picchu, just northwest of feeding and loafing together. No females were Cuzco. In this area, the Urubamba is fast sighted on this river. flowing, contains numerous large boulders within and along the edge of the river, and is Urubamba River. On our first day, we found approximately 20 m wide. Streamside vegeta- two pairs of Torrent Ducks on the 3-km tion is dense, consisting of large trees and stretch of river from Aguas Calientes to shrubs. Puente Ruines. We observed the birds perch- ing on large boulders and feeding by diving METHODS into the eddies formed downstream of rocks. The birds did not appear wary, and allowed us We conducted surveys from May 3–13, 2001 to observe them if we stayed very still by walking along the edge of the rivers at and quiet. On the following two days, we water level whenever possible. The birds were observed two pairs of ducks in the same quite tolerant of our presence and would gen- general areas as before, and one female duck erally act normally if we moved slowly along at about the 3-km mark upstream. Although the river bank. When the banks became too we observed her for 30 min, we saw no steep, we surveyed the river with binoculars sign of a male. However, it is unlikely that from above. an unpaired female would defend a territory We surveyed a total of seven km of the by herself, so we assumed that this was 271 STAUS & WEAST another pair and the male evaded detection. breeding season may be an extended one in In the 4-km stretch upstream from Aguas this population. Calientes, we observed four pairs of Torrent This stretch of the Urubamba appeared Ducks. One pair had an older (Class B) duck- quite pristine with healthy streamside vegeta- ling – all three were perched on a large boul- tion and only one small village (Aguas Cali- der together. This was the only duckling that entes) located on the river. Access to Aguas we saw during our survey. Another pair was Calientes is by train only, and the road from located approximately 300 m from a hydro- Aguas Calientes to Machu Picchu runs along electric dam/plant. the river for only 2.5 km before veering up the mountainside. Thus there is little human DISCUSSION access to the area and the river at this point may be quite healthy. This assertion is per- Torrent Ducks are ecologically limited to tor- haps supported by the fact that Peruvian Tor- rential mountain streams characterized by fast rent Duck pair densities were similar in 1965 flowing cold water moving over a substratum and 2001. There is a new hydroelectric dam of rock, stones and gravel (Johnsgard 1966). located about 4 km upriver from Aguas Cali- The birds feed primarily on insect larvae, entes, but this has not seemed to affect the especially caddis-flies, that are most abundant ability of Torrent Ducks to use this portion of in shallow riffles (Hynes 1970). Torrent the river. Indeed, we observed high pair den- Ducks have been reported in elevations rang- sities in the 7-km stretch of river immediately ing from 200 m to 4500 m, although 1500 m downstream from the dam, indicating that the is typically the low end of their distribution. river is still suitable for habitation by these Therefore, the streams we chose to survey birds. met the basic criteria for supporting Torrent To our knowledge, Quebrada Santa Cruz Ducks. has not been surveyed previously. However, Although we are unaware of a previous Torrent Ducks have been observed on the survey on the same stretch of the Urubamba Quebrada Yanganuco, another tributary of River, a tributary of the Urubamba River was the Río Santa that drains the Cordillera surveyed for Torrent Ducks in July 1965 in Blanca southeast of the Quebrada Santa Cruz, the same general area (Johnsgard 1966). The although the numbers seen were not recorded river supported a good population of Torrent (Johnsgard 1966). Because it is protected in a Ducks and the survey results suggested a national park, we assumed this river would be maximum population of about one pair per in pristine condition and able to support a kilometer over a 19-km stretch of river. Our healthy population of Torrent Ducks. survey revealed a similar pair density with six Although much of the river we surveyed pairs and one lone female observed over a 7- seemed suitable for Torrent Ducks, there km stretch of river.