Thursday, January 6, 2011

December 31 - Winter Songbird Monitoring

Temperatures had dropped considerably between the last time we were out banding and the 31st. A solid centimetre of ice had formed on all of the pools of water in the woods, which made getting to those nets considerably more difficult. At least we didn't have any snow to contend with. The wetland ponds were just about completely frozen over as well, with only a small area along the east side of the south pond remaining open and full of ducks. But we were treated to one of those few beautiful winter sunrises.

On cold days bird activity can take a little while to perk up and on the 31st it was no different. Only a few birds were caught until about an hour and a half after sunrise and most bird movement was noted after this time as well. The amount of energy needed to stay warm and move around foraging for food is probably greater than what they can gain through eating. So, for the songbirds wintering here it is probably more energy efficient to hunker down and wait for things to warm up.

It was also interesting to note that most of the birds caught had a lot of fat on them. We use a eight level system (0-7) to rate the amount of fat birds have on them. On migration birds can put on a lot of fat (typically 3-5), to be used as an energy resource to keep them going as they migrate. During the summer most birds are focused on nesting and then with replacing their feathers and most of their energy resources are put towards those activities instead of fat (typically 0-1). In the winter birds frequently put on enough fat (typically 2-3) to keep them through the night and/or through temporary food shortages caused by inclement weather. The birds must have anticipated it being a cold night and morning as most had 4-5 fat on them, with several having up to six.

Diversity was about average with 40 of the 48 birds caught were either a Spotted Towhee, Song or Fox Sparrow. Two of the most interesting birds banded most people wouldn't look twice at: Bewick's Wren (1) and Black-capped Chickadee (3). But we haven't banded a Bewick's Wren since August and the entire flock of chickadees in the woodlot had been banded, except none were seen except the three new ones. Also of note was another new Varied Thrush. This is the sixth one banded this year, all since November 21st, and none have been recaptured. It has been noted that this winter there have been higher than normal numbers of Varied Thrushes through the Vancouver area. Our banding totals likely reflect this and the lack of recaptures indicating that the habitat here isn't very suitable for Varied Thrushes. One final mention should go to the Northern Shrike that left a memorable mark on my thumb a few weeks ago. What is very likely the same bird (a banded adult shrike) is still being seen around Iona Island, primarily around the area west of the wetland ponds. It will be interesting to see how long this bird will stick around.

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