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