Observations on Syntheosciurus brochus (Sciuridae) in Volcan Poas National Park, Costa Rica

Abstract

Syntheosciurus brochus, the mountain squirrel, is a little-known Central American tree squirrel found above 1,900 m elevation in the Cordillera Central of Costa Rica and Panama (Heaney and Hoffman, 1978). The population on Volcan Poas was formerly considered a separate species, S. poasensis, but has since been united with S. brochus (Hall, 1981). The sparse literature on Syntheosciurus has dealt mainly with taxonomic problems, which are summarized in Wells and Giacalone (1985). The only information previously available concerning the ecology and behavior of this species was provided in a short note by Enders (1980). We report on the habitat, foraging behavior, courtship, and other aspects of the biology of S. brochus in Volcan Pois National Park (VPNP), Costa Rica. The squirrels were studied from 7 January to 23 March 1984, during the dry season. Several trails in and near the park were walked regularly to determine the squirrels' distribution. Observations on squirrel ecology and behavior were made through binoculars and were concentrated at feeding and nesting sites. Feeding bouts were defined as a squirrel feeding on one type of food, irrespective of length of time involved. When a squirrel switched to a different food type, a new bout was scored. Plant specimens were collected to verify identification of foods eaten by the squirrels. Two trails, one in undisturbed forest and another in disturbed forest, were indexed with distance markers and used to obtain standardized trail census estimates (Glanz, 1982). Observers walked these trials at a rate of 1 km/h for a total of 68 km. All trail census estimates in this paper are given as sightings/km. A total of 302 sightings of four squirrel species was made at VPNP. Syntheosciurus brochus accounted for 170 (56.3%) of the sightings, Sciurus granatensis 84 (27.8%), Sciurus variegatoides 15 (5.0%), and Microsciurus alfari 1 (0.3%). Identifications were based on body size, coloration, and relative lengths of ears and tails. Only 32 sightings (10.6%) were too fleeting to permit reliable identification. Not all sightings were made during designated census walks; therefore, the sum of the figures given below for specific habitats on the indexed census trails will not equal the total sightings. Squirrels were found in four types of habitats between 2,400-2,640 m: undisturbed forests, disturbed forests, shrublands, and edges. The mature, undisturbed forest where squirrels were found was situated south of the Laguna del Poas, at about 2,500 m altitude, and was classified as Lower Montane Wet by Macey (1975). Its relatively unbroken canopy was dominated by Quercus (three or more unidentified species), Clusia odorata, Didymopanax pittieri, Podocarpus sp., and Brunellia costaricensis. This forest had many trees of large girth, which were often composed of two to four species intertwined into composite trunks. Branches carried heavy loads of bromeliads, orchids, mosses, and liverworts. Sighting frequencies in squirrels/km were: S. brochus 0.46, S. variegatoides 0.02, and S. granatensis 0.42. For all squirrels combined, the sighting frequency was 1.4/km. Disturbed forest occurred on windswept slopes on the southwest side of the Laguna del Poas and the south side of the active crater, between 2,500 and 2,600 m. This forest was also regarded by Macey (1975) as Lower Montane Wet Forest. These areas were frequently subjected to volcanic gases, which may explain the low tree species diversity and the absence of bromeliads in some parts of this habitat. The dominant tree species were C. odorata, D. pittieri, Weinmannia trianea, and unidentified Quercus. Forest canopy was not continuous, and squirrels were relatively easy to see in and near tree-fall gaps. Sighting frequencies were 0.44/km for S. brochus and 0.06/km for S. granatensis. The rate for S. brochus was nearly the same in both forest habitats, but for all squirrels combined was considerably lower in disturbed forest (0.50) than in undisturbed forest (1.4). Both S. variegatoides and M. alfari were seen in disturbed forest, but not during census walks. Shrublands above 2,500 m had been created by volcanic activity, road construction, and clearing for pastures. These large patches and strips of habitat fit Macey's (1975) categories termed arrayan and pasture edge. They contain shrub species, such as Vaccinium consanguineum, V. poasanum, Myrica February 1987 145