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cause the hormonal changes that will send him on his way. At this tim
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For a number of years I have had a male and female hummer at the back of =
my lot - presumably they have had a nest there although I have never =
seen any young. This year I have not seen a male hummer, but a female is =
around almost every day. I don't go looking for nests because I don't =
think it is wise to disturb nesting birds, but I think there is probably =
a nest there tended by the female with the male having deserted the poor =
girl.
Roland.
----- Original Message -----=20
From: Peter Payzant=20
To: naturens@chebucto.ns.ca=20
Sent: Sunday, June 24, 2007 12:38 PM
Subject: Re: [NatureNS] Why do male hummers...
So, even if a male hummer is suitably fattened up to begin the =
migration south, he still has to wait for the shortening days to cause =
the hormonal changes that will send him on his way. At this time of =
year, the day length is changing very slowly (think of the top of a sine =
curve), so presumably the hormones won't start flowing for at least a =
few weeks until the days are noticeably shorter. Even if it makes sense =
in every respect for the males to be on their way, they won't know it =
until the shortening day length sends them the message.
Peter
----- Original Message -----=20
From: Wild Flora=20
To: naturens@chebucto.ns.ca=20
Sent: Saturday, June 23, 2007 10:23 PM
Subject: RE: [NatureNS] Why do male hummers...
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.
=20
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:=20
a.. 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.=20
b.. 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.=20
c.. the early fall departure of the males may leave a richer diet =
available for the developing young of the year.=20
=20
=20
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...
=20
Hi, all-
=20
Here's a question that I ponder from time to time: Why do male =
hummingbirds wait around here all summer before migrating south?
=20
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.=20
=20
Why don't they just go back south once the females are sitting on =
nests?
=20
I can think of a few not-very-convincing reasons:
=20
- The environment here (food, shelter, weather, predation pressure) =
might be better than on their southern range
=20
- Some resources that they need on migration are not yet ready (e.g. =
some important flowers not generating nectar yet)
=20
- There's always a chance that an un-mated female will turn up (I =
call this the "wishful thinking" hypothesis)
=20
Any other thoughts?
=20
Peter Payzant
Waverley
=20
=20
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No virus found in this incoming message.
Checked by AVG Free Edition.=20
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6/24/2007 8:33 AM
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