I found this one sitting on the ground near the bird bath I was filling. Of course I didn't have a camera with me, but he/she was still there when I went back with the camera in hand.
Could those feathers get any more fluffy?
The bird appeared healthy enough, with its alert eyes following me as I walked around it. It moved into the sun a few minutes later, and then flew off into the weeds near the bird feeder.
Fall weather is hard on all us homeotherms, as we try to rev up the metabolism that keeps us warm. Acclimation to cold typically takes a few weeks as increased thyroid hormone helps us increase heat production and changes in blood flow to the skin reduce heat loss. Decreased hours of daylight here in the far north means less time for animals to fatten up during the day to fuel the metabolic furnace overnight. Maybe these little guys (they only weigh 12-15 grams, about the same as a fast food ketchup package) just run out of energy on those colder nights and need more time to rewarm during the morning. I know mortality is much higher in the fall than in the middle of winter for these small birds. Once they get fully acclimated to cold they can withstand temperatures as low as -70 F for a few hours, and -40 F for 8-12 hours (based on studies done by a colleague in Michigan many years ago).
How different these drab winter plumaged birds are from their golden summer color. Here are two Goldfinches sitting in the same part of the garden, on the stems of Purple Coneflower. (click on any of the photos to enlarge to full size)
Fall weather is hard on all us homeotherms, as we try to rev up the metabolism that keeps us warm. Acclimation to cold typically takes a few weeks as increased thyroid hormone helps us increase heat production and changes in blood flow to the skin reduce heat loss. Decreased hours of daylight here in the far north means less time for animals to fatten up during the day to fuel the metabolic furnace overnight. Maybe these little guys (they only weigh 12-15 grams, about the same as a fast food ketchup package) just run out of energy on those colder nights and need more time to rewarm during the morning. I know mortality is much higher in the fall than in the middle of winter for these small birds. Once they get fully acclimated to cold they can withstand temperatures as low as -70 F for a few hours, and -40 F for 8-12 hours (based on studies done by a colleague in Michigan many years ago).
How different these drab winter plumaged birds are from their golden summer color. Here are two Goldfinches sitting in the same part of the garden, on the stems of Purple Coneflower. (click on any of the photos to enlarge to full size)
How cute! I had no idea Goldfinches changed their plumage so drastically throughout the year.
ReplyDeleteI didn't either. I'll have to look more carefully because we do have several Goldfinches around in the summer - also quite a few Chickadees and a few other tiny birds that I'm not sure of.
ReplyDeleteThe bright plumage of the Goldfinch male is designed to show off to females in the summer; the rest of the year both sexes seem to adopt the camouflage strategy instead. This is typical of many bird species, but not Chickadees, Nuthatches, and Woodpeckers whose bold patterns are constant throughout the year.
ReplyDeleteI was surprised to read about the Goldfinch and their camouflage strategy. I am sure that I have seen them, but assumed they were some other tiny bird. Thanks, too, for the reminder about the onset of cold and our adaptation to it. Brrr. I am liking cold weather less and less each year.
ReplyDeleteBut just think how warm 40 degrees will feel to us in February, compared to now. That's when you really appreciate your ability to adapt to cold. thanks for the comments.
ReplyDelete