Hi all, This past weekend I spent some time backpacking along the crest of the Cascade Mountains near Glacier Peak. My second night, I woke up to a deer (initially thought to be a bear) in camp at about 4:30 AM at Buck Creek Pass (~5700'). I was on edge enough afterwards that I decided to stay up and hear out the rest of the night as the marine layer was nonexistent that morning. At about 5:00-5:15AM there was a 5 minute window where SWAINSON'S THRUSHES started doing their nocturnal flight calls all around me. Some were definitely already on the ground in the forest, but there were others that were actively calling overhead. As abruptly as it started, it ended without another 'peep'. I also had a CHIPPING SPARROW or two fly over during this time.
I think the Cascade Mountains provide an extremely interesting case of the unknown influences of weather and topography on migration. There were flocks all over the our 30+ mile hike along the crest that contained dozens of Yellow-rumped Warblers, Chipping Sparrows, with a smattering of Townsend's, MacGillivray's Warblers, etc. still hanging around...yet how these birds decide to migrate through and out of the area I find to be an interesting question. There is often a marine cloud layer (flat gray stratus that act as fog when you're in them) that are often backed up against the west side of the Cascade Mountains between 2000-6000 ft ASL (sometimes deeper). This presents a problem because there are a lot of hills and mountains in that elevation range so a bird flying in the fog could potentially just fly into a mountain. So I'm assuming most of these birds either do one of four things when they decide to move south...1) they migrate altitudinally to the Puget Sound/Seattle/Portland areas and migrate southward underneath the marine layer or 2) fly up and over the Cascade crest to migrate on the typically much clearer and drier (usually no marine layer exists) east side of the Cascade Mountains or 3) fly up above the marine layer in between the highest peaks at (7000-10000 ft) and/or 4) only migrate on days where the marine layer doesn't exist. I've always found how birds migrate in complex topography to be fascinating and an extremely interesting question...and certainly this marine layer just adds a little more spice to the question for those in the Pacific NW. Colby -- NFC-L List Info: http://www.NortheastBirding.com/NFC_WELCOME http://www.NortheastBirding.com/NFC_RULES http://www.mail-archive.com/nfc-l@cornell.edu/maillist.html --
