Numerous birders have told me of "bilingual" birds. Although most folks don't use Ned Johnson's terminology, which I recommend, I think most such reports refer to the MPN, which is indeed problematic. So far I have thought of four possible explanations for such reports. Which is correct, in each case, would be readily apparent if recordings were available of these "bilingual" birds. So, get out your recording devices and bring back the goods! Meanwhile, here are the possibilities that have occurred to me: Bilinguality. A single bird uses standard COFL MPN and standard PSFL MPN. I know of one verifiable example: Kevin Colver has a tape of a bird singing PSFL Advertising Song that also produces a few standard COFL MPNs along with standard PSFL MPNs. COFL Variability. Because the great variability of COFL MPN is not widely appreciated, observers who hear a continuous, rising, COFL MPN may assume it is a PSFL MPN. If the bird also utters two-parted MPNs, it may then be called "bilingual." Duetting. A pair duetting with different forms of MPN may be construed as a single bird with two kinds of MPN. If these are different enough, bilinguality may be invoked. Song Phrase 2. This is the most interesting and plausible alternative to true bilinguality. I visited the site of a famously bilingual bird in Oregon (in a subsequent year) and recorded a bird that was indeed giving two different sounds in mid-morning, when the MPN is the most likely sound to be used. Spectrograms revealed that the two sounds were (1) MPN and (2) Song Phrase 2. This bird was foraging and tooling around the territory, calling sporadically, as males do in mid-summer. Some of the calls were MPN, others were Song Phrase 2. The interesting thing about this "Song Phrase 2 Hypothesis" is that Song Phrase 2 is continuous in COFL and broken in PSFL, just the OPPOSITE of the standard MPN of these forms. For either species, alternating its MPN and SP2 at a time of day when MPN is usually the only sound could easily give the impression of bilinguality! Bear in mind that both species also may insert the MPN into the rapidly repeated Advertising Song at dawn. Construing a Male Position Note as a Song Phrase 2 at this time could also give the impression of bilinguality. The bottom line, in my opinion, is that before you accuse a bird of being bilingual, you must be able to discriminate four different sounds, both MPN and Song Phrase 2 of both species. That doesn't mean bilingual birds aren't out there. Send me a recording of a bilingual bird and I'll put it on this site. Home Introduction     Characteristics of Sounds     List of Geographic Samples