The winter storm we had this past weekend provoked a flurry of emails from customers concerned for the hummingbirds in their yards. One email read, "I have a hummingbird who is still hanging around, notwithstanding the cold weather. Because he's still here I have been keeping the feeder supplied, although I have to take it in every night so it doesn't freeze. I certainly don't mind doing this, but I'm wondering if I'm doing the right thing; that is, by keeping the feeder supplied and accessible am I inducing him to stay here when he would otherwise migrate to a warmer climate? On the other hand, if I take the feeder down, might he die from the cold or lack of food? I don't think I could stand it if he died when I could have kept him alive. What's your advice?"
Another email read, "It seems like we are getting more and more hummingbirds during the winter. Do you think it is possible that a subspecies or a variety of Anna's or black-chinned hummingbirds is starting to evolve that are resistant to the cold temperatures? Those of us like myself that keep a feeder out during the winter are obviously encouraging this to happen. I understand that hummingbirds go into a state of torpor during the cold winter nights, but why do just a few hummingbirds hang around during the winter and most go south? Just wondering."
It is one of the wonders of nature that hummingbirds can survive our winter weather. The one species of hummingbird that winters over in the Central Arizona Highlands is the Anna's hummingbird. It weighs approximately 4.4 grams! In spite of its diminutive size, Anna's hummingbird are uniquely adapted to winter weather with its ability to go into a state of semi-hibernation referred to as torpor.
On cold winter nights, Anna's hummingbirds lower their body temperature between 40 and 50 degrees to reduce the amount of energy they need to expend to survive. It was 18 degrees Monday morning at my house. A hummingbird's normal daytime temperature is 104 degrees. The differential in temperature on Monday between body temperature and air temperature was a whopping 86 degrees! If hummingbirds didn't have the ability to lower their body temperature, they would have to expend a tremendous amount of energy (while sleeping) to keep their body temperature at 104 degrees. By lowering their body temperature 40 degrees, the difference between their body temperature and the air temperature would only be 46 degrees, cutting their energy demand almost in half.
My response to the first email was, "At this point, you would be wise to keep the feeder out during the day. If you are concerned about inducing a hummingbird to stay, the time to take the feeder down is in the fall, not in the dead of winter when they probably would die if the feeder were suddenly removed."
My response to the second email was, "One thing that happened this year was an incredibly mild fall and winter - I don't know that hummingbirds felt a need to migrate. It is likely more are wintering over because of the human activity of providing feeders, but Anna's have always had the ability to go into torpor, and are hearty birds, capable of withstanding very cold temperatures."
I invite you to attend the Prescott Audubon Society meeting at 7 tonight in the fellowship hall at Trinity Presbyterian church, located at 630 Park Avenue. The speaker for this evening's program is David Moll, and his program is titled, "The White Mountains of Eastern Arizona." It should be an excellent meeting, and I hope to see you there. Until next week, Happy Birding!