[cobirds] West & East Warbling Vireo

Hi

Recently there has been exciting chatter that Colorado could be the home for both the "eastern" and "western" populations of the Warbling Vireo. Further speculation implies these two populations may reflect two different Warbling Vireo species! Within the eastern and western populations there are intermediate populations, thereby causing extreme difficultly in physical identification for each group. It has been suggested that the best way to separate the two groups is by song, the western group apparently ending its song on an upward inflection and the eastern on a downward inflection. Downward-inflected songs have been noted on the eastern plains, leading to the assumption that the eastern group may be present in that region. On a recent family trip encircling the West Elk Mountains in Gunnison, Montrose, and Delta counties, I decided to don my citizen scientist sun hat and see what the Warbling Vireo sounded like in that region of the state.

A usual pattern of their song began to emerge. Frequently the song would consist of two sequences, the first sequence ending on an upward inflection and the second sequence ending on a downward inflection or a neutrally-inflected note. In addition, the song would often consist of one sequence ending with an upward inflection, and infrequently the song would include just one sequence that ended on a downward inflection. Sometimes the song of either sequence would be sung repeatedly of just one sequence or the other.

So what can be learned from this brief experiment in citizen science that produced a mixed message about the sound of the western population of Warbling Vireo? Does the variation in the sequence of the Warbling Vireo song represent a normal pattern of variation within the species and with each of the Vireo's two populations?
Does the variation in the song pattern reflect a phase of the Vireo's phenology as it does with some other species where the song pattern and length changes depending on if the bird is in territorial, breeding, or after breeding mode? Could time of day indicate what song variation is being sung?

There seems to be a lot more that is unknown than known, and we in Colorado could contribute be being alert to what song is being sung when and where.

Bob Righter
Denver, CO

Sent from my iPad

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