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Posted by Alex Harper on 12:01:54 03/29/11
In Reply to: Re: Meterology and Migration posted by Toe
Global environmental issues aside, the driving force behind cold fronts is the solar radiation budget in the polar region. If the polar region receives an especially cold winter (a degree or so less than average), it will produce very high pressure, cold, dense air. That polar air will move south across the continent into areas of lesser resistance, displacing warmer and less dense air originating from the more tropical regions. The difference in pressure systems is the cause for wind, and the steeper the gradient in pressure (associated with difference in land temperature), the faster the wind. A more mild polar winter means that southern, warmer winds will be able to reach farther north and more frequently. There are more considerations to take in, such as ocean currents and temperature, making this even more complicated.
So yes, warmer winters allow for more frequent and prevailing southern winds that could (I emphasis "could") allow spring migrants to follow.
Whether this is even altering migration to any degree, partly an anthropogenic cause, or just a natural global cycle, etc., I don't know. Just food for thought, and we might have to give this more attention as an environmental community in years to come.
While doing a passerine survey here at the university, I failed to find any migrants other than Chimney Swifts which have been here for a few days now. Winds over Mexico and Cuba are blowing from the south. The winds will shift sometime Thursday with a cold front, and depending on timing and duration of the front, force birds to take landfall along the Gulf. By tomorrow there should be more accuracy as to when the cold front will arrive. Hopefully in the early morning hours in my area (or yours).
Alex
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