Subject: [Tweeters] Anna's Feeder Competition
Date: Jan 6 13:01:55 2011
From: David Hutchinson - flora.fauna at live.com



Hummingbirds, in general, are opportunists, certainly exemplified by our local ANHU. There are really two questions here: 1) Does male competition limit female survivorship based on feeder use? I know of no evidence that this is true, while humans seem to be adding feeders along with the expanding hummer population?. The sex ratio in ANHU is skewed in favour of males in any case. Traditionally West Coast hummingbird females are heavier than males, which may enhance their competitive abilities. However in S.Calif males are heavier than females, about which I won't speculate.
2)Is female Annas' ability to raise young hampered by male competition at feeders? Based on my feeder study in Magnolia/Discovery Park the answer is clearly no.Females appeared to drastically cut back their use of feeders once they were incubating The hatching of their young seems to correlate closely with the blooming of local native woodland species, such as Red Flowering Currant, followed by Salmonberry and many other native and introduced ornamentals. With all the mild temperatures we have had recently, the first bloom of Indian Plum in our forests and green belts cannot be far away.
Similarly Rufous Hummingbird nesting in our latitude is timed around the blooming of Salmonberry, irrespective of what garden plants are available. Another question of interest is: What effect does inter-specific competition between Annas and Rufous have. While perhaps smaller Rufous tends to dominate Annas at feeders if only through sheer numbers at feeders. But Annas fledge well before Rufous and could be second-nesting while Rufous fledge. There is evidence that Annas can double clutch here. I don't know what the story is for Rufous however.

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