From: hoyerr@ucs.orst.edu (Richard Hoyer)
Newsgroups: rec.birds
Subject: Re: Hummingbird health question
Date: 23 Nov 92 19:55:52 GMT
Article-I.D.: gaia.1erd08INNafb
Organization: University Computing Services - OSU
NNTP-Posting-Host: ucs.orst.edu

In article <41238@sdcc12.ucsd.edu> afong@sdcc13.ucsd.edu (Krell Kraver) writes:
>Is it true that hummingbird feeders should be removed in the early
>fall so that the little guys will migrate (since there's no
>food).???
>
>Thanks for the help.



	It depends entirely on your interest and you location whether 
	you should keep a hummingbird feeder in the winter.  Pulling a
	feeder down in order to make hummingbirds migrate is like 
	pulling the shades down in order to make the sun set.  Migration
	is not intstinctive in all hummingbirds, but for those species 
	which do migrate, it is an incredibly strong instinct.  And there
	is nothing a person can do to prevent a Rufous Hummingbird, for 
	example, from migrating--short of holding one captive.

	It is pretty clear that migration is genetically controlled, with
	probably some learned influence for some species.  In hummingbird 
	species that migrate, it is probably enitirely genetic.  Imagine
	what would happen to those that failed to inherit the correct
	genes for migration--they would starve in the winter.  On top of 
	that, migration for hummingbirds (again, only those that live in
	cold-winter areas) must be very strictly controlled.  This is 
	because hummingbirds have very high metabolic rates and need a
	relatively constant supply of high-energy food; and that is not
	always easy to find.  So, during the evolution of migration in 
	hummingbirds, the proper genes have been selected.  The genes
	dictate, for example that the hummingbirds "feed up" just before
	migrating, so that they build-up just the right amount of body
	fat.  They cannot be too heavy, or they will exhaust themselves
	and will not make it to their destination (where there is more
	food).  And if they do not build up enough fat, they will deplete
	their energy supplies before reaching their destination.  In addtion
	dictating how much migrating hummingbirds feed, genes also must 
	control when this is done.  Obviously, hummingbirds must be able to
	build up this fat deposit while there is still food around.  And
	one will notice that hummingbird migration is timed when there 
	still is an abundance of wild food for them.  Over thousands and
	thousands of years, hummingbirds that have varied from this strict
	schedule have simply died.

	 
	But there are hummingbird species that do not migrate.  These are
	species that live in areas where there is food year round.  In
	this case, leaving up a hummingbird feeder in the winter is just
	like putting up a seed feeder for the other birds.  In the San Diego
	area, there are two species of non-migratory hummers:  Anna's 
	Hummingbird and Allen's Hummingbird.  The Allen's is sedentary, and
	the Anna's has unusual wandering patterns.  The Anna's used to be
	native to central and southern California, where wild currants
	bloomed in the winter.  After breeding, Anna's Hummingbirds move 
	around to set up new territories; some tend to move from hills
	into valleys, and some just tend to go further.  In the past, those
	that wandered too far, out of the range of any source of winter
	food died.  But in the past century, people have kept hummingbird
	feeders up in the winter, and as a result, the Anna's Hummingbirds
	have instead survived.  In subsequent years, they have also spread
	farther, and now are permanent residents up the West Coast to
	British Columbia.

	One other reason to keep a hummingbird feeder up in the winter
	is to attract those stray hummingbirds that did not follow their
	migration insticts.  These hummers would have normally died, if
	their error caused them to migrate east instead of south.  But
	if somebody in the East (Missouri for example) were to keep a
	feeder up in the winter, they might actually attract one of
	these lost birds.  Rufous Hummingbirds and Black-chinned Hummers
	have been known  to do this. Keeping a feeder up for this reason
	is only for the person interested in the exitement of finding
	a rarity.

-Rich Hoyer
 
Newsgroups: rec.birds