Western Bonelli’s Warbler

Alternating Song Trills

Went to see this amazing record. An early July Western Bonelli’s Warbler on the edge of Manchester. Rather unprecedented! It was not too difficult to hear with sufficiently regular song trills. These came in very short bursts. Seeing it though a lot harder. When  I finally got reasonable views it was a rather colourless looking thing. Greenish fringes on wing and faint yellow on rump  rather tricky to discern due to the worn plumage. It’s constant movement didn’t help in trying to get a good view of the plumage characters either. I did manage some OK recordings of the song trill. I also heard 3-4 times a ho-eet type call which I think was it, but couldn’t be absolutely sure.

These sonagrams were fascinating for me and a learning experience. I didn’t notice a difference in the song trill in the field, though it did seem very short. Notice how there are 2 types of song trill on the sonagrams. They correspond  roughly to song trills:  Bonelli’s type 1 and Bonelli’s type 3 in this Dutch Birding paper. Interestingly the bird was actually alternating between these 2 trill types. The following is a sequence of 6 song trills, in the order in which the bird sang during a  period of 2 minutes and 6 seconds. It’s pretty consistent:

4th July 2011: (click through for larger sizes)