Tuesday, February 21, 2006

goldfinch update and notes on Sibley

About a month ago I posted about an unusually yellow goldfinch that had been hanging around my feeder. I did not see that particular goldfinch this weekend, but I did find out more about what causes bright yellow colors in goldfinches, courtesy of the Minnesota Birding Network listserv. Someone else asked about the same thing, and this was the response:
The brightness of plumage for the American Goldfinch is an indicator of the
amount of carotenoids the bird ingests during the molting period. A friend
of mine, who works with AMGO and their carotenoid pigments, suggested that
the bird may have ingested a larger amount of carotenoids during the molting
period (vs. his flock mates). Maybe the reason he is so yellow is because
he is an "aggressive" bird and able to outcompete his buddies. Another
possible argument is that he may have lived in a different area during his
molt where the foraging was better. Hope this helps.
So the yellow guy may be a superfinch.

I was perusing through my new copy of The Sibley Field Guide to Birds of Eastern North America last night, and while I like the format overall and the amount of information given for a small, pocket-size guide, I came across a couple of statements that I questioned. About the Great Blue Heron: "Nests in colonies in dead trees..." I have seen several great blue heron nesting colonies, and the trees they are in were all very much alive. Sometimes the nesting activity of the herons, and the accumulation of waste, ends up killing the trees, but I have seen one particular colony at least once a year since 1971, and very few trees have been lost.

The other statement, on the immediately preceding page, regarding the American Bittern: "Uncommon in marshes, where it hides among grasses and reeds, its cryptic plumage blending in with the vegetation." I once believed that bitterns were so secretive that I had little chance of ever seeing one. That is, until I encountered this brazen bittern last summer.

Despite these discrepancies, I think Sibley's guide clarifies some things that my 20 year old Petersen's and 35 year old Birds of North America failed to. For example, I was mystified by the woo-woo-woo sound produced by the wingbeats of one bird here in the spring, and neither of my books offered much help. Sibley clearly identified it as a Wilson's snipe, which must be a relatively new name for that species.

I'm hoping to get out in the marshes and woods more this spring and identify more of the species that are no doubt here, but which I have not taken the time to see or hear.


madcapmum said...

"Cryptic plumage" - what a great description.

Chris O'Byrne said...

About three years ago, the name was changed from Common Snipe to Wilson's Snipe. I believe that before it was called Common Snipe, it used to be called... Wilson's Snipe! Some organizations simply have too much time on their hands. Perhaps a DNA analysis indicated that Jack Wilson really was genetically related to this particular species of snipe. ;)

clairesgarden said...

malls are bad places, but you can never have too many books!

shannon said...

Up in Ithaca, there's a small colony of blue herons who do nest in a large stand of dead trees - but weather it was the nesting activty that killed the trees...who knows! :) I used to take my kayak onto the pond and row to the nesting island to read.

lené said...

Interesting observations about the herons and their impact on trees, Deb. I would love to see a bittern. Your bittern moon post was pretty amazing, as well.

bev said...

Regarding Great Blue Herons, in my area (eastern Ontario), most herons seem to nest in dead trees in beaver-flooded forest. However, there is a colony not too far from my place that is in the tops of some very tall Red Pines. I shot a bit of video footage of them a couple of years ago. I've just made a still photo from the video footage and put it up on my website in case you want to take a look. Because it's a frame grab, it's not that clear, but I think you'll still be able to see the adult to the left, and the nest with 3 young heron standing up in it over to the right. There were several tall pines with nests in them and I believe they've been there for at least several years.

As for American Bitterns, we've occasionally had them nest in an old drainage ditch that runs through our farm. We see and hear them from time to time. The adults sometimes wander out into the meadow and seem to think they are well camouflaged when they stand very still with their beaks pointed in the air pretending they are cattails, but they're rather obvious looking because they're the only thing stickiing up from the grass. About 20 years ago, I had a very young bittern turn up wandering around in my vegetable garden. Somehow, it must have wandered up from the drainage ditch. When I approached it, it went into the typical bittern pose with its beak up in the air while it kept its eyes on me. I left it where it was and it wandered off again in awhile.