Path: utzoo!attcan!uunet!decwrl!sdd.hp.com!zaphod.mps.ohio-state.edu!rpi!leah!gmr044
From: gmr044@leah.Albany.Edu (Gregg Recer)
Newsgroups: rec.birds
Subject: RE: Bird feeding and migration
Keywords: feeding migration range expansion etc.
Message-ID: <3438@leah.Albany.Edu>
Date: 2 Aug 90 15:53:54 GMT
Organization: The University at Albany, Computer Services Center
Lines: 56


Various posts have brought up the idea that summer/fall feeding of
birds might interrupt normal migration behavior in birds so fed.  I
think there's no strong generalization that can be made about this
issue.  I doubt very much that bird species with strong migration
tendencies will hang around in great numbers just due to the presence
of some feeders in a typical non-winter-range area.  On the other
hand, some populations in which not all individuals are strongly
migratory may respond to additional food availability in fall and hang
around.  Northward range expansions of some species such as N.
Cardinals and N. Mockingbirds have been explained, at least in part,
by this kind of effect.  I believe this kind of thing has helped
Anna's Hummers expand their range north as well, yes?  

     I guess the main point is that, for migratory species, the main
cue to which they respond is day-length.  Shorter light cycles cause
physiological changes that result in a whole suite of behaviors
leading to (in our case) migration southward.  Most often, food levels
are correlated with decreasing day length (insects, e.g. die or become
inactive as fall progresses) so the advantage in migrating may be in
moving to areas with more food but the main cue to which the birds
respond is not food per se but light (light cycle-length is a whole
lot less variable from year to year than is food abundance so it's a
more useful cue).  In species where the response to the light cue is
not real strong food levels could act as a secondary cue to modify
migratory behavior.

     One condition that is not generally a factor in this is
temperature.  Birds are typically quite well adapted to surviving cold
temperatures.  So hanging around in the cold northern winter, wouldn't
necessarily be a "disaster", as someone suggested, assuming there was
sufficient food around.  The main reason the typical winter-resident
bird species here in the northeast are chickadees, nuthatches,
woodpeckers and finches is that these species can either dig dormant
insects out from under bark, etc. or can subsist pretty much entirely
on various seed crops available in the winter.

     As a side note, with regard to sugar-water for hummer feeders,
nectar, which I'm sure hummers eat without incident, is sugar water
(basically fructose instead of sucrose).  This soft-bill idea is
pretty silly, seems to me.



Gregg



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     "In future you should delete the words crunchy frog and 
     replace them with the legend crunchy raw unboned real
     dead frog!!"  
                 -- Inspector Bradshaw, The Hygiene Division

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