Sexual Selection in the Gray Catbird
birds have disproportionately focused on species with pronounced sexual
dimorphism and polygynous mating systems. Several of 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.