Central American birds have slightly different song structures and also tend towards lighter ochre plumage independent of Gloger's Rule; they are sometimes separated as flammulated attila ("Attila flammulatus") . Their characteristic song given at dawn has been analyzed in detail: it has a very variable number of "weery"s which may become "weery'o"s, and often ends in a "woo-whit"; a finite state machine has been developed to simulate this structure. However, due to the highly variable songs more data is required before the technically plausible split can be accepted; the AOU has so far refrained from formally acknowledging it.