Friday, January 8, 2010

Found another goldencheek

It wasn't in today's flock, but after we were done with that and scouted for tomorrow's location, we did find one. We drove about a kilometer further on the road where we found a flock this morning, just to make sure that tomorrow's location would be Tracker accessible. You don't want to discover that it isn't at six in the morning. We've found that our Chevy Tracker has rather low clearance and gets into trouble where in previous years the pick-ups we drove had no problems at all.

As we came up on a part of that road where in a previous field season we had found a goldencheek, I noticed how suddenly there were thin-leaved oaks everywhere. Knowing now what we didn't know then, it just made sense that this is where we found that goldencheek back then. And sure enough, within a few minutes after exiting the car, we found another one. Today's bird was an immature female, with only a little bit of black on the sides of the breast, and a clear throat and chin. We'll look for it again tomorrow - maybe I'll get some photos. The bird pictured above is a male Hepatic Tanager, a common bird here in La Botija and a regular flock member. Today's flock had four.

Driving back, I wondered why it seems to be that goldencheeks on the wintering grounds prefer thin-leaved oaks, while the species they associate with appear to be more generalist. Think about it: structurally, a goldencheek isn't that much different from a black-throated green, yet the BT green is found in a much wider variety of microhabitats. (It also is a lot more numerous, of course.) I think part of the answer may be that BT greens employ a wider array of foraging strategies, utilizing treetops as well as the middle layer, and occasionally even the herbaceous layer, feeding on all parts of the substrate. Goldencheeks on the other hand are often found in either the tree or middle layer, foraging on the outer branches of the tree.

Why is this?

Is the BT green a slower, more methodical forager, and the goldencheek a faster-paced forager that needs more light so it can discover prey more quickly?

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