Social Grooming in the Brown-headed Nuthatch may have Expanded Functions James A. Cox* Abstract - Allopreening is a form of social grooming that has not been extensively studied in most birds. Observations of allopreening in Sitta pusilla (Brown-headed Nuthatch) are described where sex, age, and kin relationships were known for the individuals performing the behavior. Young of the year allopreened adults and nest mates, adult male helpers allopreened breeding females and unrelated adults, and breeding adults allopreened one another as well as young of the year. Previous observations suggested allopreening served to maintain pair bonds in the Brown-headed, but these observations suggest the behavior may have expanded functions. Although most allopreening focused on neck and head regions where the behavior may primarily serve hygienic functions, wings and backs also were allopreened frequently in a manner consistent with the social functions suggested for other birds. Allopreening, a form of social grooming performed by birds, has been documented for scores of avian taxa, but the functions of the behavior are not well understood (Radford and Du Plessis 2006). Allopreening is assumed to have important hygienic functions in many species, but allopreening may also include social functions such as maintaining pair bonds and social hierarchies or reducing strife among group members and neighbors (Lewis et al. 2007, Radford and DuPlessis 2006). The paucity of information on social grooming in birds contrasts sharply with the situation for mammals, where social grooming has been documented as a major feature of social living (Radford and Du Plessis 2006). Allopreening has been documented frequently in Sitta pusilla Latham (Brown-headed Nuthatch), but, because most observations involved unmarked individuals, the sex and relationships of individuals engaged in the behavior were largely unknown (Withgott and Smith 1998). For example, Barbour and DeGange (1982) described allopreening between two nuthatches and suggested the behavior might assist in maintaining pair bonds. Barbour and DeGange (1982) did not describe how sex was ascertained for the individuals they observed, but sex cannot be determined accurately in this species based exclusively on plumage (Withgott and Smith 1998). The Brown-headed Nuthatch also frequently lives in family groups that contain ≤5 members and include breeders and non-breeding helpers (Cox and Slater 2007). Nuthatches observed allopreening cannot be assumed to be a breeding pair or even a male-female combination. In this note, I provide new details on allopreening in the Brown-headed Nuthatch based largely on observations of marked individuals recorded during the post-breeding period. Since 2003, a large, individually marked population of Brown-headed Nuthatches has been maintained on Tall Timbers Research Station (30.66°N, 84.22°W; Leon County, FL) by placing unique color-band combinations on an average of 39.3 adults and 72.1 nestlings annually. Methods used to mark adults and nestlings are described in Cox and Slater (2007). In 2011, I monitored post-fledgling activities by re-sighting the adults and marked fledglings associated with 17 territories. The territories were visited for 20 min on 2–4 occasions each month from May through November, and territorial responses were elicited by playing recorded nuthatch vocalizations that included aggressive calls *Tall Timbers Research Station, 13093 Henry Beadel Drive, Tallahassee, FL 32312. Corresponding author - jim@ttrs.org. Notes of the Southeastern Naturalist, Issue 11/4, 2012 771 772 Southeastern Naturalist Vol. 11, No. 4 and contact and foraging notes (Norris 1958). Individuals were identified by reading color band combinations using a spotting scope (30–60x zoom), and all surveys were conducted between 06:30 and 11:00 DST. Allopreening was defined as a behavior where the bill of one nuthatch made contact with the feathers of another individual in a preening motion. Ten instances of allopreening were observed, and the behavior was classified as reciprocal when individuals preened one another simultaneously or in succession (Barbour and DeGange 1982). Kin relationships and social status (i.e., breeder versus helper) for adults were based on pedigree data and behavioral observations made during the breeding season and followed Cox and Slater (2007). Although most territories with ≥3 adults appeared to have a dominant breeding pair and non-breeding helpers (Cox and Slater 2007), extra-pair copulations have been documented infrequently in territories with ≥3 adults (K. Han, University of Florida, Gainesville, FL, unpubl. data) and indicate that some helpers may also be breeders. I use the term helper to refer to individuals that appeared to differ in social status based on observations of copulation and other behaviors. Juveniles represented nestlings marked prior to fledging, and sex for all individuals was based on DNA samples collected and processed following Haas et al. (2010). All observations of allopreening took place in settings identical to those described by Withgott and Smith (1998), where individuals perched side-by-side on horizontal limbs. Allopreening may take place throughout the year (Withgott and Smith 1998), but my earliest observation occurred on 1 July (approximately 8 weeks after nestlings fledged), while my latest observation occurred on 17 November. The observations typically lasted ≤2 min before individuals resumed other activities. Three observations involved ≥1 unbanded adults where relationships could not be assessed (including one instance of reciprocal allopreening). The remaining observations were recorded in 7 independent territories and involved color-marked birds where sex, age, and status could be assigned. 1 July: a helper male allopreened the breeding female for approximately 40 sec while the breeding male sat on a nearby limb. The dominant male was observed sitting near the female later during the survey, and there were no hostile interactions between the helper male and breeding male. 7 July: a breeding male allopreened the breeding female for approximately 35 sec without reciprocation. 15 August: a breeding male allopreened a juvenile male for approximately 1 min without reciprocation. 6 September: a breeding male and juvenile male engaged in reciprocal allopreening for approximately 1 min. 14 October: a breeding male from a neighboring territory allopreened a juvenile male without reciprocation for approximately 30 sec. The breeding male was the grandfather of the juvenile male. 21 October: a helper male allopreened the breeding male without reciprocation for 20 sec. 17 November: a breeding female and 2 juvenile males engaged in reciprocal allopreening for approximately 1.5 min. The female and a juvenile simultaneously preened the second juvenile perched between them. Approximately 20 sec before interactions ceased, the female moved to the middle and was allopreened by both juvenile males. Social grooming in mammals is thought to serve both hygienic and social functions, but allopreening in birds has been viewed largely in terms of hygienic benefits because 2012 Southeastern Naturalist Notes 773 the behavior appears to concentrate on body areas that are difficult or impossible for individuals to reach (Brooke 1985, Harrison 1965). Recent work on Phoeniculus purpureus Miller (Green Woodhoopoe) provides a new framework for evaluating social versus hygienic functions by considering the area on a recipient’s body where a donor allopreens (Radford and Du Plessis 2006). When allopreening is focused around the neck, head, and other areas difficult to reach with the bill (hereafter head preening), the behavior may serve a hygienic function. Alternatively, when allopreening is directed toward wings, backs, and other areas that can easily be reached with the bill (hereafter body preening), the behavior may serve a social function. In the Green Woodhoopoe, the frequency of head versus body allopreening varies in relation to season, social dominance, and social setting and suggests the behavior has multiple functions (Radford 2008, Radford and Du Plessis 2006). Although I did not quantify the specific time spent allopreening head versus body areas, most donors directed their efforts toward head and neck areas in agreement with a hygienic function. Donors were observed touching the back, wing, and belly less frequently, but allopreening body areas occurred regularly and was consistent with the social function described for the Green Woodhoopoe. Body allopreening was particularly common in the 17 November observation where two donors allopreened a recipient. In addition, the Brown-headed Nuthatch has a shorter bill than the Green Woodhoopoe that enables individuals to reach portions of the neck that individual woodhoopoes can not. Donor nuthatches that allopreened around the neck would be difficult to classify using the head/body criterion established by Radford and Du Plessis (2006). Allopreening in the Brown-headed Nuthatch appears to serve functions other than maintenance of the pair bond emphasized by Barbour and Degange (1982). I observed male and female breeders grooming juveniles, adult helpers grooming adult breeders, and juveniles grooming juveniles. Norris (1958) also described reciprocal allopreening between an adult male and helper male from a neighboring territory. Allopreening in the Brown-headed Nuthatch may serve multiple functions, but additional data are needed to assess the relative importance of allopreening for hygienic versus social functions. It may seem daunting to collect behavioral data for a small songbird (11 g) that forages in the canopy, but I observed approximately 0.15 allopreening events per hour of observation (while also attempting to collect other data). This rate is similar to the ≈ 0.30 allopreening events recorded per hour by Radford and Du Plessis (2006). Future studies also should attempt to monitor the behavior both with and without the use of playback vocalizations. The playback vocalizations elicit territorial responses that could influence the frequency of allopreening as well as the body areas where allopreening is focused (Radford 2008). Acknowledgments. This study was supported by the Wildlife Research Endowment at Tall Timbers Research Station. I also thank an anonymous reviewer for helpful comments on an earlier draft. Literature Cited Barbour, D.B., and A.R. DeGange. 1982. Reciprocal allopreening in the Brown-headed Nuthatch. Auk 99:171. Brooke, M. 1985. 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