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According to the http://www.hummingbirds.net website, male hummingbirds and
female hummingbirds are on a different migration schedule. (See below.) As
to why they don't migrate any sooner, the main reason is that they migrate
in response to hormonal changes that are triggered by changes in daylight.
However, this probably confers a survival advantage because it gives them
more time to fatten up before they make that long journey. They need to get
to something like double their normal weight before they start out.
According to Connie Toops's book "Hummingbirds: Jewels in Flight," banding
studies suggest that hummers will postpone migration if they are
underweight. This is why it's probably a good idea to keep feeders up late
into the fall.
Here's what the hummingbirds.net site has to say about hummingbird gender
differences in migration:
Male hummingbirds migrate northward as much as three weeks earlier in the
spring than females. In the fall, the mature males similarly leave earlier
than females and immature birds. [Males may start migrating as early as July
in some areas.] Several reasons are generally offered for this behavior:
* by arriving first, the earliest males have their choice of the best
territories, which improves their chances of attracting females for
breeding. But this advantage must be balanced against the risk of arriving
before food is plentiful.
* females - who will soon be nesting - will find more and
better-developed flowers on the spring migration route if they leave
somewhat later; in promiscuous species such as hummingbirds, which do not
form pair bonds at all, breeding females are more valuable than males, and a
reliable food supply reduces their risk.
* the early fall departure of the males may leave a richer diet
available for the developing young of the year.
From: naturens-owner@chebucto.ns.ca [mailto:naturens-owner@chebucto.ns.ca]
On Behalf Of Peter Payzant
Sent: Saturday, June 23, 2007 8:24 PM
To: naturens@chebucto.ca
Subject: [NatureNS] Why do male hummers...
Hi, all-
Here's a question that I ponder from time to time: Why do male hummingbirds
wait around here all summer before migrating south?
Once they've mated with a female, their purpose here is essentially over.
They don't help in taking care of the young, and there's only one brood per
female per year. In fact, you could say that the males create a negative
reproductive pressure by competing with the females and young for food.
Why don't they just go back south once the females are sitting on nests?
I can think of a few not-very-convincing reasons:
- The environment here (food, shelter, weather, predation pressure) might be
better than on their southern range
- Some resources that they need on migration are not yet ready (e.g. some
important flowers not generating nectar yet)
- There's always a chance that an un-mated female will turn up (I call this
the "wishful thinking" hypothesis)
Any other thoughts?
Peter Payzant
Waverley
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<p class=3DMsoNormal><span =
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color:#1F497D'>According to the <a =
href=3D"http://www.hummingbirds.net">http://www.hummingbirds.net</a>
website, male hummingbirds and female hummingbirds are on a different =
migration
schedule. (See below.) As to why they don’t migrate any sooner, =
the main
reason is that they migrate in response to hormonal changes that are =
triggered
by changes in daylight. However, this probably confers a survival =
advantage
because it gives them more time to fatten up before they make that long
journey. They need to get to something like double their normal weight =
before
they start out. According to Connie Toops’s book =
“Hummingbirds:
Jewels in Flight,” banding studies suggest that hummers will =
postpone
migration if they are underweight. This is why it’s probably a =
good idea
to keep feeder