Sexual Selection in the
Gray Catbird
Studies of sexual
selection in
birds have disproportionately focused on species with pronounced sexual
dimorphism and polygynous mating systems. For the past three
summers, my REU students (pictured from left to right: Jake Langeslag,
Greg Sours, Dhyana Miller) have investigated how sexual selection might
operate in a sexually monomorphic, apparently monogamous species, the
Gray Catbird (Dumetella carolinensis).
The Gray Catbird is a neotropical migrant that winters from the Gulf
states south into to Panama. In Virginia Catbirds return to breed
in mid to late April and can produce as many of three broods within a
single breeding season before returning south in September and October.
The Gray Catbird is a member of the Mimidae, the mockingbird
family. Like other members of that family, it is an accomplished
singer, with a double syrinx that allows it to make unusually
complicated sounds. Only males sing. The Catbird's song is
a
long, rambling string of phrases. We have been recording Catbirds
in order to quantify their vocabularies and to relate vocal patterns to
male pairing success, male parental care, and nesting success.
Although Gray Catbirds are sexually
monomorphic, they do possess two conspicuous, though simple, plumage
ornamentations. Males and females have a dark black cap and both
have chestnut-colored undertail coverts. Both of these ornaments
are the result of melanin-based pigments and reflect light strictly in
the visible range. Both are variable within each
sex. We have begun to examine whether these ornaments can act as
informative signals of mate quality. Using standardized digital
photos we have been able to quantify color variation and relate this
variation to age, male pairing success, male and female parental
care (both sexes feed nestlings), and male and female nesting
success. We are also interested in how multiple signals (song and
plumage) interrelate with one another.