Today Matt Young told me about David Sibley’s recent post on vocal mimicry in Pine Siskins. The surprise to me (and to Sibley and others) was not that Pine Siskins infringe on other birds’ copyrights, but rather that this fact had gone unreported in the literature for so long. Actually it hadn’t just gone unreported; it had been refuted. For example, the Birds of North America account on Lesser Goldfinch says:
Mimicry of other species in [Lesser Goldfinch's] song repertoire, first documented by Dawson (1923), is a characteristic shared with Lawrence’s, but not with Pine Siskins or American Goldfinches. (Other cardueline species known to display interspecific mimicry are Purple Finch [Carduelis purpureus], Cassin’s Finch [Carpodacus cassinii], and Greenfinch [Carduelis chloris; Guttinger 1977]).
In addition to the above species, the Pine Grosbeak is an excellent and frequent mimic (Adkisson 1999). Mimicry has also been documented in House Finches (Sewall & Hahn 2003), although apparently only once, in an anomalous bird.
Evening Grosbeaks and the three rosy-finches are members of the Carduelinae, but they don’t sing complex songs as their relatives do; in all four of these species it’s likely that long series of call notes serve the basic functions of song. Interestingly, although several early authors reported that Evening Grosbeaks and Black Rosy-Finches sing soft warbling or twittering songs, modern authors typically do not mention them, and sound recordings of these musical “songs” are rare or nonexistent. Perhaps the early authors were handicapped by a basic conviction that all songbirds must have a song.
The remaining North American Cardueline finches (redpolls and crossbills) have not been reported to mimic other species, although I’d be surprised if the Red Crossbill, at least, never mimicked, as its song is so tremendously variable. I find it fascinating that some species mimic while their close relatives do not. Why do Lesser and Lawrence’s Goldfinches mimic, but not American? Why do Cassin’s and Purple Finches mimic, but not House Finch (usually)? Perhaps House Finch and American Goldfinch are mimics, but such poor ones that we don’t recognize their attempts as mimicry?
What do you think? Any reports of mimicry out there that haven’t made it into the literature?