[Tweeters] Anna's Dive Noise
flora.fauna at live.com
Thu Mar 5 13:42:16 PST 2009
I believe that what the illustrious Mr. Ed Swan is hearing is the Dive Noise produced by Anna's Hummingbird at the nadir of the elongated oval which the male makes on its display territory. A variety of display flights by West Coast hummers, partic Rufous and Allens are apparently made by wing noise i.e. vibration not unlike the winnowing of Snipe. However there has been much debate over the source of the male annna's noise. One person placed a feather on the end of a whip, cracked it and was convinced therefore that if was feather noise. It is a conundrum that one does not hear that noise, which I hear as PEEK!! during the summer months. This is because adults are moulting their rectrices so cannot control a dive, but also hormonally they cannot sing - so this does not give a clue. Younger males may attempt it though.Rearchers like Gary Stiles and Stephen M.Russell have also gone back and forth on this issue. However in his BNA monograph, Russell ascribes the noise to the bird's voice. I personally agree with this. Having listened to Anna's vocalizations on display territory, the quality of the PEEK noise has the same quality as the male's voice and also sounds like the chattering noise that males often make in a chase. However, surprsingly nobody has recorded and slowed down the noise into a helpful sonagram. I am therefore placing my bet, but I am prepared to be wrong. There is still much to be learned about Anna's e.g. what is the full significance of sex skewed numbers i.e. there are more males than females in a population. And most intriguing of all: in all west coast hummingbird species, the females are larger than the males. Not true for Anna's, the only one to have males larger than females!! I do not believe this is adequately addressed in the literature. I have my own hypothesis as to why this might be so. Can you all think of a plausible explanation?? Perhaps a book prize for the best explanation, which shall include several of the unusual factors in Anna's breeding system. Happy Hunting, David Hutchinson
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