Ruby-throats in winter

Date: Wed, 14 Nov 2001 07:06:31 EST
From: Bob Sargent <RubyThroat@AOL.COM>
Reply-To: BB for Hummingbirds and Gardening for them in the Southeast
<HUMNET-L@listserv.lsu.edu>
To: HUMNET-L@listserv.lsu.edu
Subject: Re: [HUMNET-L] November 10, LA Western Winter Hummer report #14

Rob and Humnetters:
Our crew of banders have certainly found more Ruby-throated in recent
winters. I THINK that the increase is due to the more diligent search going
on, and, to some lesser degree to the fact that the milder weather has
allowed a greater survival rate of those that did not migrate. In my
experience, most Ruby-throated that attempt to winter in the USA will fail
unless they are doing so in the area near the Gulf Coast. Even in mild
winters, few have been known to successfully survive away from the coast.

An added note:
It APPEARS to me that Ruby-throated are not very good at putting on fat oncethat window of time for migration has passed. I suspect that this
hormone-driven process does have a set of time limitations. This would be
unlike Rufous and some of the other species that can fatten daily as the
temperatures requires for survival. As winter deepens, it is my OPINION that Ruby-throated are not particular skilled at using torpor as a defense against the chill of winter nights.

It has been my experience that when a bitter winter occurs, the number of
Ruby-throated that "disappear" in our study area is almost 100%. By the way, most Ruby-throated that are found away from the coast in winter have some kind of physical defect or injury that is easily noted when in the hand.
This was long ago suggested by Newfield in personal conversations. Things
like damaged and deformed bills, wounds, damaged flight feathers, damaged
feet, bill lesions, etc. While some Ruby-throated will survive mild winters,
Mother Nature does not take kindly to most of them that stray from the normal migration timing patterns she has long established. There is a great wisdom in that scenario in my opinion.

God Bless
Bob Sargent

======================================================

Date: Wed, 14 Nov 2001 17:32:40 +0000
From: "Nancy L. Newfield" <colibri@GS.VERIO.NET>
Reply-To: BB for Hummingbirds and Gardening for them in the Southeast
<HUMNET-L@listserv.lsu.edu>
To: HUMNET-L@listserv.lsu.edu
Subject: Re: [HUMNET-L] November 10, LA Western Winter Hummer report #14

Bob and Y'All,

At 07:06 AM 11/14/01 EST, Bob Sargent wrote:

>Our crew of banders have certainly found more Ruby-throated in recent
>winters. I THINK that the increase is due to the more diligent search going
>on, and, to some lesser degree to the fact that the milder weather has
>allowed a greater survival rate of those that did not migrate.

I've had no indication that the Ruby-throats we see in winter are in fact
birds that failed to migrate. The ones we get are [as best I can tell]
individuals that have come from elsewhere. Whether they came from elsewhere down the block or from a distant corner of eastern North America we cannot tell, but most of the time these birds show up after a period of weeks during which no Ruby-throats have been present. I think of these guys in much the way I consider the Western/Mexican birds - that is they are
individuals that migrated from somewhere else to our neck of the woods
rather than individuals that did not migrate.

> In my
>experience, most Ruby-throated that attempt to winter in the USA will fail
>unless they are doing so in the area near the Gulf Coast. Even in mild
>winters, few have been known to successfully survive away from the coast.

Of course, southeastern Louisiana is much more temperate than most of the
area you cover. I strongly suspect that Ruby-throateds [and Black-chinneds,
too] are less cold tolerant than Rufous, Broad-tailed, and Calliope, but we
have had success stories. It was a very long time before I had any winter
Ruby-throat returnees, but now we have recorded several. Still, the number
of winter Ruby-throat returnees doesn't come close to the number of
Buff-bellied returnees though we've handled similar numbers.

>It has been my experience that when a bitter winter occurs, the number of
>Ruby-throated that "disappear" in our study area is almost 100%. By the way,
>most Ruby-throated that are found away from the coast in winter have some
>kind of physical defect or injury that is easily noted when in the hand.
>This was long ago suggested by Newfield in personal conversations. Things
>like damaged and deformed bills, wounds, damaged flight feathers, damaged
>feet, bill lesions, etc.

In my experience, Ruby-throats will be the first to "disappear" in freezing
weather, but some are able to survive. Most of the ones we see don't appear
to be damaged, but rather they are very young or retarded in their
developement. We find 80%-90% bill corrugations in January. Ordinarily,
that percentage is what we see in Ruby-throats in August and September and we don't see bill corrugations to that extent in wintering Rufous. Molt is often delayed.

I have often puzzled over the approximate hatching dates of these guys and
never came up with anything plausible. Fred Bassett suggested to me that
these birds were possibly delayed in their developement and that is probably
the correct scenario. Maybe this was originally your idea.