Warbling vireo - How exactly do you "warble"?

A warbling vireo near Merritt, BC.

"The warbling vireo is one of the most abundant and familiar breeding birds in deciduous stands throughout most of British Columbia" (quote from BC breeding bird atlas).   I find this statement odd, in that I have lived in BC now for almost 40 years and this is the first one I have ever photographed.  

Warbling refers to "the act of singing or producing a melodious sound with rapid changes in pitch, vibration, or tone" (from Merriam-Webster).  If you listen to the song (click here for video), you will notice that the bird does indeed warble.

The warbling vireo has been split into two species, the western and the eastern species.  They look similar and can be difficult to tell apart.  I photographed this bird near Merritt, BC, so it is likely a western warbling vireo.  There is a great image of both birds here.  The differences are minute, and I can't be sure that it is the western variety, but it makes sense given where I photographed it.  Their ranges mix in the prairies, and I was well west of there.

A mated pair will aggressively defend their nest by chasing larger birds such as jays and magpies.  They "mob" the intruders by joining a group of other songbirds and harassing them until they leave the area.  We have all seen smaller birds chasing after larger ones; it seems that mobbing behaviour is found in many species of birds, which may work cooperatively to banish would-be nest predators.  The behaviour includes chasing, using harsh calls, excitedly flitting around, and even dive-bombing them.  Such behaviour decreases predation and increases brooding success.

The warbling vireo - the singing mobster.

Thanks for reading.

Eric Svendsen     www.ericspix.com