Acta Chiropterologica, 11(1): 208–211, 2009 PL ISSN 1508-1109 © Museum and Institute of Zoology PAS doi: 10.3161/150811009X465839 Remaining cryptic during motion — behavioral synchrony in the proboscis bat (Rhynchonycteris naso) MIRJAM KNÖRNSCHILD 1, 4 , CHRISTINA HARVIEW 2 , RACHEL MOSELEY 3 , and OTTO VON HELVERSEN 1 1 Department of Zoology, University Erlangen-Nürnberg, Staudtstrasse 5, D-91058 Erlangen, Germany 2 Department of Biology, Bryn Mawr College, 101 N. Merion Avenue, Bryn Mawr, PA 19010,USA 3 Department of Biology, Bucknell University, 701 Moore Avenue, Lewisburg, PA 17837, USA 4 Corresponding author: E-mail: mknoerns@biologie.uni-erlangen.de Key words: Rhynchonycteris naso, cryptic roosting, behavioral adaptation, synchronous rocking, grooming, urinating SHORT NOTES INTRODUCTION Most bat species inhabit roosting sites in which they are well concealed during the day, such as caves or tree holes, whereas others roost in exposed locations on tree trunks or branches (Kunz and Lum- sden, 2003). For the latter, it is essential to appear cryptic in order to avoid predation or disturbance at the day-roost. Several traits have evolved to enhance the bats’ cryptic appearance, including cryptic col- oration (e.g., the greenish wings of the foliage-roost- ing bat Paranyctimene raptor — Bonaccorso, 1998) or disruptive markings (e.g., the contrasting meta- carpals and phalanges of the tent-roosting flying fox Cynopterus brachyotis — Kunz and Lumsden, 2003). Behavioral habits may also aid in camouflag- ing roosting bats. One remarkable example is the ‘leaf wrapping behavior’ exhibited by the Australian flute-nosed bat Murina florium, which conceals these foliage-roosting bats effectively from visually oriented predators (Schulz, 1999). In general, there are many more known examples of morphological adaptations for cryptic roosting than there are of behavioral adaptations (Kunz, 1982; Kunz and Lumsden, 2003). Remaining completely motionless during the day is a behavioral habit that obvious- ly assists in camouflage, but it conflicts with the bats’ need for comfort behavior, such as grooming or stretching. We studied the cryptic roosting habits of the pro- boscis bat, Rhynchonycteris naso. This neo-tropical member of the emballonurid family roosts in very exposed areas on tree trunks, branches, vines or man-made structures which are in close proximity to running water (Bradbury and Emmons, 1974). Group size is intermediate, and ranges from 5 to 50 individuals of both sexes (Bradbury and Vehren- camp, 1976). Individuals of small groups normally roost in a vertical line, whereas larger groups tend to form ovals (Bradbury and Emmons, 1974). Indepen- dent of group size, a vertical line is always formed when individuals roost on structures with a small diameter, such as thin trunks, branches and vines (authors’ personal observation). Despite its exposed day-roosts, R. naso is physically very cryptic due to the woolly and mottled pelage with two wavy pale lines on the back and tufts of pale hair on the fore- arms (Dalquest, 1957; Bradbury and Vehrencamp, 1976). This protective camouflage allows the roost- ing bats to resemble a patch of lichen or moss (Hill and Smith, 1984). Bradbury and Emmons (1974) first reported a ‘synchrony in grooming periods by group members’ and ‘frequent periods of gentle rocking’, a stereotypic behavior in which the bats sway rapidly from side to side while both feet and wrists remain attached to the surface of the roost. This peculiar behavior occurs frequently during the day and is often exhibited synchronously by many or all group members, but it is not triggered by dis- turbance. When startled or approached, the bats do not rock, but instead remain motionless before they fly off together. Therefore, the functional signifi- cance of rocking has remained unclear (Bradbury and Emmons, 1974), but a somewhat related behav- ior in arachnids, termed whirling or bobbing, is pro- posed to provide a camouflage defence against pred- ators (Jackson, 1990; Heuts et al., 2001; Grether and Donaldson, 2007). Group members of R. naso not only synchronize rocking and grooming but also uri- nating (authors’ personal observation), but the bene- fit, if any, of this behavioral synchrony is unknown.