It is a good question.  I don't know whether there's a dispersal after a 
snow storm, but many birds apparently try to stick it out given the 
large numbers of birds that show up by the roadsides.  Nevertheless, 
White-throated Sparrows and Dark-eyed Juncos obviously migrate south for 
the winter. And I expect part of the reason is to avoid areas of 
permanent snow cover.  (BNA online notes regarding White-throated 
Sparrows that "In central Canada, spring migrants arrive when snow melt 
exposes portions of forest floor; latest departures in fall are prior to 
first permanent snowfall.")  White-throated Sparrows are found in Maine 
in winter, but primarily in the south and along the coast where it is 
warmer and snow cover is likely not permanent.  (Dark-eyed Juncos follow 
a similar pattern).  Having, recently moved from Massachusetts, I can 
also attest to the fact that White-throats are much more common in 
Maryland in winter than further north in Massachusetts, where snow is 
likely to linger longer.

Jim Moore
Rockville, Maryland

Andy Martin wrote:
> Thanks Frank. Come to think of it, after big storm in Dec, I did 
> observe both Horned Larks and Savannah Sparrows using the "ground 
> raised" height effect of snow cover to feed off tall weed and grass tips.
>
> Andy Martin
> Gaithersburg
>
> Frank Marenghi wrote:
>>
>> Hi Andy,
>>
>> Good question. I doubt it though. White-throats, White-crowned, 
>> Juncos, Song Sparrows, and many other feeder-type ground birds 
>> regularly winter in regions that have snow cover throughout the 
>> entire winter (Maine, Nov. or Dec. - April). To say nothing of field 
>> birds, Snow Buntings, Longspurs, etc. I think these birds utilize 
>> other foods (i.e., berries, grass seeds, sap) or use open areas 
>> (wind-blown areas, roadsides, etc.). Bird feeders almost certainly 
>> help out certain species significantly. N. Cardinals for example are 
>> expanding their range northward, possibly because of an increase in 
>> winter feeding by humans.
>>
>> My personal feeling is that ground hunting raptors like Harriers 
>> might suffer more.
>>
>> Best,
>>
>> Frank
>>
>>
>>
>> > Date: Sun, 7 Feb 2010 10:42:25 -0500
>> > From: 
>> > Subject: [MDOSPREY] question about snow cover and bird movement
>> > To: 
>> >
>> > With extraordinary snow cover in place in parts of MD, do some regular
>> > winter residents (White-throateds, juncos and other birds somewhat
>> > dependent on ground feeding) make a secondary migration out of the 
>> area?
>> >
>> > Andy Martin
>> > Gaithersburg
>> > 
>>
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>