Re: Fate of the hummingbirds?

In article <smhcc21gpdmh3ura48bq2ime1crdclk132@xxxxxxx>,
maryann kolb <mkolb@xxxxxxxxxx> wrote:

the adult birds are fat. In fact the male
looks like a feathered ping-pong ball. the juveniles on the other
hand are just little slivers. It makes me wonder how many of them
will make it all the way to their winter grounds. I hope they stick
around and get a lot fatter before they try it.

The first adult males started migrating a couple of weeks ago; they
don't all leave at the same time. Most adult females will leave in
August, and immature birds will follow when they're strong and fat
enough, mostly in September. Some birds nearly double their weight
before departing--so fat they can barely fly! But at that weight, they
can fly nonstop for about 600 miles without eating, which gives them a
nice cushion against the uncertainties of migration.

It's nearly impossible to tell when your summer birds have left, because
they look the same as all the ones from farther north that will be
passing through on their own migrations.

Does anyone know the attrition rate?

Since the overall population of Ruby-throated is essentially stable,
attrition from all causes is essentially the same as the birth rate.
There's not a lot of data, but one study put average annual survivorship
at 31.2% for males and 42.3% for females. In another study, recapture
rates suggested that immature males are 2 to 3 times more likely to die
than older birds.

Yes, an inexperienced hummer's first migration is hard and dangerous.

--
Lanny Chambers
St. Louis, USA
http://www.hummingbirds.net/
.

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