next message in archive
next message in thread
previous message in archive
previous message in thread
Index of Subjects
Index of Subjects
This is a multi-part message in MIME format.
--Boundary_(ID_la24JuoQ8S6w4XWvU0sGGw)
Content-type: text/plain; charset=iso-8859-1
Content-transfer-encoding: 7BIT
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 -----
From: Wild Flora
To: naturens@chebucto.ns.ca
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.
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:
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.
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.
c.. 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
__________ NOD32 2349 (20070623) Information __________
This message was checked by NOD32 antivirus system.
http://www.eset.com
--Boundary_(ID_la24JuoQ8S6w4XWvU0sGGw)
Content-type: text/html; charset=iso-8859-1
Content-transfer-encoding: quoted-printable
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML xmlns=3D"http://www.w3.org/TR/REC-html40" xmlns:v =3D=20
"urn:schemas-microsoft-com:vml" xmlns:o =3D=20
"urn:schemas-microsoft-com:office:office" xmlns:w =3D=20
"urn:schemas-microsoft-com:office:word" xmlns:m =3D=20
"http://schemas.microsoft.com/office/2004/12/omml"><HEAD>
<META http-equiv=3DContent-Type content=3D"text/html; =
charset=3Diso-8859-1">
<META content=3D"MSHTML 6.00.2900.3132" name=3DGENERATOR>
<STYLE>@font-face {
font-family: Wingdings;
}
@font-face {
font-family: Wingdings;
}
@font-face {
font-family: Calibri;
}
@font-face {
font-family: Tahoma;
}
@font-face {
font-family: Verdana;
}
@page Section1 {size: 8.5in 11.0in; margin: 1.0in 1.0in 1.0in 1.0in; }
P.MsoNormal {
FONT-SIZE: 12pt; MARGIN: 0in 0in 0pt; FONT-FAMILY: "Times New =
Roman","serif"
}
LI.MsoNormal {
FONT-SIZE: 12pt; MARGIN: 0in 0in 0pt; FONT-FAMILY: "Times New =
Roman","serif"
}
DIV.MsoNormal {
FONT-SIZE: 12pt; MARGIN: 0in 0in 0pt; FONT-FAMILY: "Times New =
Roman","serif"
}
H2 {
FONT-WEIGHT: bold; FONT-SIZE: 15.5pt; MARGIN-LEFT: 0in; MARGIN-RIGHT: =
0in; FONT-FAMILY: "Times New Roman","serif"; mso-style-priority: 9; =
mso-style-link: "Heading 2 Char"; mso-margin-top-alt: auto; =
mso-margin-bottom-alt: auto
}
A:link {
COLOR: blue; TEXT-DECORATION: underline; mso-style-priority: 99
}
SPAN.MsoHyperlink {
COLOR: blue; TEXT-DECORATION: underline; mso-style-priority: 99
}
A:visited {
COLOR: purple; TEXT-DECORATION: underline; mso-style-priority: 99
}
SPAN.MsoHyperlinkFollowed {
COLOR: purple; TEXT-DECORATION: underline; mso-style-priority: 99
}
P {
FONT-SIZE: 12pt; MARGIN-LEFT: 0in; MARGIN-RIGHT: 0in; FONT-FAMILY: =
"Times New Roman","serif"; mso-style-priority: 99; mso-margin-top-alt: =
auto; mso-margin-bottom-alt: auto
}
SPAN.EmailStyle17 {
COLOR: #1f497d; FONT-FAMILY: "Calibri","sans-serif"; mso-style-type: =
personal-reply
}
SPAN.Heading2Char {
FONT-WEIGHT: bold; mso-style-priority: 9; mso-style-link: "Heading 2"; =
mso-style-name: "Heading 2 Char"
}
.MsoChpDefault {
FONT-SIZE: 10pt; mso-style-type: export-only
}
DIV.Section1 {
page: Section1
}
OL {
MARGIN-BOTTOM: 0in
}
UL {
MARGIN-BOTTOM: 0in
}
</STYLE>
<!--[if gte mso 9]><xml>
<o:shapedefaults v:ext=3D"edit" spidmax=3D"1026" />
</xml><![endif]--><!--[if gte mso 9]><xml>
<o:shapelayout v:ext=3D"edit">
<o:idmap v:ext=3D"edit" data=3D"1" />
</o:shapelayout></xml><![endif]--></HEAD>
<BODY lang=3DEN-US vLink=3Dpurple link=3Dblue bgColor=3Dwhite>
<DIV><FONT face=3DArial size=3D2>So, even if a male hummer is suitably =
fattened up=20
to begin the migration south, he still has to wait for the shortening =
days to=20
cause the hormonal changes that will send him on his way. At this tim