Kentucky Ornithological Society
Kentucky Warbler 76:48-50, 2000
 

The Forehead Patch of Tufted Titmice:

A Possible Status Signal
 
 

Shawn P. Moses and Gary Ritchison
Department of Biological Sciences
Eastern Kentucky University
Richmond, KY 40475 USA



Abstract.-- Among birds, morphological features, called status signals or badges, may provide information about relative fighting ability and, as such, permit birds to avoid costly fights. Tufted Titmice (Baeolophus bicolor bicolor) have black forehead patches that vary in size, and our objective was to determine the possible relationship between patch size and dominance status in winter flocks in central Kentucky. Patch width was significantly correlated with dominance rank, with higher ranking birds having wider patches. Such results suggest that the forehead patch of titmice might serve as a status signal, particularly during encounters between unfamiliar individuals. Variation in patch size may also be an important intersexual signal.
 
 

    Status signals are morphological features that convey information about relative fighting ability. These signals may allow assessment of potential competitors and permit birds to avoid costly fights with dominant individuals (Rohwer 1975). In birds, prominent plumage patterns often function as status signals and such signals have been reported in several species, including the House Sparrow (Passer domesticus; Møller 1987) and Dark-eyed Junco (Junco hyemalis; Yasukawa and Bick 1983). Status signals have also been reported among species in the family Paridae, including Great Tits (Parus major; Jarvi and Bakken 1984, Wilson 1992) and Willow Tits (P. montanus; Hogstad and Kroglund 1993). Among North American parids, Otter and Ratcliffe (1999) found that bib morphology varies among Black-capped Chickadees (Poecile atricapillus), but the signal value of such variation remains unclear. Similarly, Tufted Titmice (Baeolophus bicolor bicolor) have black forehead patches that vary in size among individuals. The objective of  our study was to determine if the size of these forehead patches is correlated with dominance status in winter flocks of titmice in Kentucky.
 
    During the non-breeding season, Tufted Titmice occur in small flocks of 2 - 5 birds that typically consist of a pair of adults plus a variable number of juveniles (offspring and juveniles from unknown natal sites) (Grubb and Pravosudov 1994, Pravosudova et al. 1999). Dominance hierarchies develop within these flocks and flock members may also interact with titmice from other flocks (Brawn and Samson 1983, Grubb and Pravosudov 1994). Thus, as with other flocking species, Tufted Titmice might benefit from the presence of a status signal.
 

METHODS

    We studied titmice at the Central Kentucky Wildlife Management Area (CKWMA), located 17 km southeast of Richmond, Madison County, Kentucky. Beginning in September 1996, six feeding stations were stocked with sunflower seeds.  From October 1996 through February 1997, titmice visiting these stations were captured in mist nets and banded with numbered aluminum bands plus a unique combination of colored bands.  The size of the forehead patch (top width, bottom width, and height) was also determined. From December 1996 - March 1997, titmice were observed at feeding stations to determine the dominance relationships among flock members. During interactions at feeders, an individual was considered dominant if it either chased or supplanted another titmouse or if another titmouse waited nearby and did not visit the feeder until the dominant bird left.
 

RESULTS

    We captured 29 titmice, and were able to determine the age of 13 (4 hatching year and 9 after-hatching year) (Pyle et al. 1987). AHY birds had longer (Mann-Whitney U test, P = 0.02) wing chords (mean length = 81.3 mm) than HY birds (mean length = 76.8 mm), but AHY and HY birds did not differ (P > 0.15)  in tarsus length, tail length, mass, or any measure of patch size (top width, bottom width, height, or total area).
 
    Fifteen titmice were observed throughout the study and formed five flocks, with flock size ranging from 2 to 5 birds. Dominance hierarchies in titmouse flocks are linear peck-right, with each member of a flock consistently either dominant or submissive to other flock members (Brawn and Samson 1983). For all flocks combined, we observed an average of 2.9 interactions per dyad and, based on these interaction, assigned each flock member a dominance rank. We found a significant correlation between rank and patch width (measured along the top of the patch), with higher ranking birds having wider patches (rs = 0.55, n = 15, P = 0.032). Correlations between the width of the bottom of the patch and rank and between patch area and rank, respectively, approached significance, with higher ranking birds having both wider (rs = 0.44, n = 15, P = 0.099) and larger patches (rs = 0.47, n = 15, P = 0.07).  The height of the forehead patch was not correlated with rank  (rs =0.002, n = 17, P = 0.99).
 

DISCUSSION

    The significant correlation between the width of the forehead patch of Tufted Titmice and dominance status suggests the patch may serve as a status signal. However, the results of  previous studies of titmice also suggest that variation in patch morphology may be important only during intrasexual interactions with unfamiliar individuals and as an intersexual signal. Several factors appear to support this hypothesis. First, dominance status within flocks of titmice is typically age- and sex-related, with males dominant to females and, within a sex, adults dominant to juveniles (Brawn and Samson 1983). If so, and assuming that male titmice were the top-ranked individuals in the flocks observed during our study, the observed correlation between patch size and status in our study may have due, in part, to sex-related differences in plumage. In addition, flocks of titmice are stable (Samson and Lewis 1979) and often composed of parents and offspring (Pravosudova et al. 1999). As a result, flock members typically know, and know the status of, other flock members, making status signals unnecessary.
 
    However, even badges that reflect age or sex may serve as a signal of potential fighting ability among unfamiliar individuals (Lemel and Wallin 1993). Thus, status signaling may be important during encounters between members of different flocks because they might not remember the fighting ability of birds with which they interact only rarely (Jarvi and Bakken 1984).  Because they interact occasionally with conspecifics from other flocks and with satellite birds with no flock membership (Brawn and Samson 1983, Grubb and Pravosudov 1994), titmice might benefit from the presence of a status signal.
 
    Morphological variation in the forehead patch of Tufted Titmice may also be important as an intersexual signal. For example, Norris (1990a, b) found that female Great Tits may use the breast stripe of males as a criterion for mate choice, and may benefit from such discrimination because large-striped males are more attentive to the nest and more likely to defend the brood. Similarly, female House Sparrows prefer large-bibbed males as mates, and such males tend to obtain better territories and nest sites (Møller 1988). Additional study is needed to determine the possible role, if any, of the forehead patch in the mate choice decisions of male and female Tufted Titmice.
 

ACKNOWLEDGMENTS

    We thank Joel Beverly for help with the field work, and the Eastern Kentucky University Research Committee for financial support
.

LITERATURE CITED

Brawn, J. D. and F. B. Samson. 1983. Winter behavior of Tufted Titmice. Wilson Bull. 95:222-232.

Grubb, T. C., Jr. and V. V. Pravosudov. 1994. Tufted Titmouse (Parus bicolor). In The Birds of North America, No. 86       (A. Poole and F. Gill, eds.). The Academy of Natural Sciences, Philadelphia, PA; The American Ornithologists’ Union, Washington, DC.

Hogstad, O. and R. T. Kroglund. 1987. The throat badge as a status signal in juvenile male Willow Tits, Parus montanus. J. Ornithol. 134:413-423.

Jarvi, T. and M. Bakken. 1984. The function of the variation in the breast stripe of the Great Tit (Parus major). Anim. Behav. 32:590-596.

Lemel, J. and K. Wallin. 1993. Status signalling, motivational condition and dominance: an experimental study in the Great Tit, Parus major. Anim. Behav. 45:549-558.

Møller, A. P. 1987. Variation in badge size in male House Sparrows Passer domesticus: evidence for status signalling. Anim. Behav. 35:1637-1644.

Møller, A. P. 1988. Badge size in the House Sparrow, Passer domesticus. Effects of intra- and intersexual selection. Behav. Ecol. Sociobiol. 22:373-378.

Norris, K. J. 1990a. Female choice and the evolution of conspicuous coloration of monogamous male Great Tits. Behav. Ecol. Sociobiol. 26:129-138.

Norris, K. J. 1990b. Female choice and the quality of parental care in the Great Tit Parus major. Behav. Ecol. Sociobiol. 26:275-281.

Otter, K. and L. Ratcliffe. 1999. Relationship of bib size to age and sex in the Black-capped Chickadee. J. Field Ornithol. 70:567-577.

Pravosudova, E. V., T. C. Grubb, Jr., P. G. Parker, and P. F. Doherty, Jr. 1999. Patch size and composition of social groups in wintering Tufted Titmice. Auk 116:1152-1155.

Pyle, P., S. N. Howell, R. P. Yunick, and D. F. DeSante. 1987. Identification guide to North American passerines. Slate Creek Press, Bolinas, CA.
 
Samson, F. B. and S. J. Lewis. 1979. Experiments on population regulation in two North American parids. Wilson Bull. 91:222-233.

Watt, D. J. 1986. Relationship of plumage variability, size and sex to social dominance in Harris’ Sparrows. Anim. Behav. 34:16-27.

Wilson, J. D. 1992. A re-assessment of the significance of status signalling in populations of wild Great Tits, Parus major. Anim. Behav. 43:999-1009.
 
Yasukawa, K. and E. I. Bick. 1983. Dominance hierarchies in Dark-eyed Juncos (Junco hyemalis): a test of a game-theory model. Anim. Behav. 31:439-448.


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