Local birder Jack Hayden scored a phenomenal sighting in the Native Plant Area of Cesar Chavez Park around noon on August 29: a Ruby-throated Hummingbird. When he first spotted it, he figured it was another Anna’s Hummingbird, which are seen frequently in that area and elsewhere, but this bird looked smaller. When it did him the great favor of settling on a branch and resting for a bit, he got a series of images that sent him to the internet, to the books, and on email to hummingbird experts. After several days the verdict came in, in the form of an opinion by Sheri Williams, author of the Peterson Field Guide to Hummingbirds of North America: it’s a juvenile male Ruby-throated Hummingbird. No such bird has ever been spotted in Alameda County, and there have only been 21 recorded sightings in all of California, ever.
The differences between the common Anna’s and this rara avis are minute. Here’s Williams’ decision: “The mask is darker than usual in juvenile male Black-chinneds, and the tail notch is quite deep, exposing the black tips of R3-4, and the third photo shows the diagnostic elongated oval tip on P5 and the sharply pointed P6.” Hayden’s photos on eBird are at this link.
The Ruby-throated Hummingbird is an East Coast native. It’s the only hummer that breeds on the East Coast, and when it does, it’s quite bold and unafraid of people. It’s by far the most common hummingbird seen east of the Mississippi River. It breeds widely on the East Coast as far north as Canada. It may come in numbers not only to feeders but also to potted plants on a windowsill, and it may sometimes build its tiny nest on human structures. In the fall it migrates across the Gulf of Mexico, often in an uninterrupted flight of 500 to 900 miles, to Central America. Some individuals skip the Gulf crossing and spend the winters in Florida. When breeding, the female does all the work; she builds the nest, sits on the eggs and feeds the babies, while the male flits about. She may even build a second nest and start a second brood while still feeding the first.
They have an amazing metabolism. “Hummingbirds have one of the highest metabolic rates of any animal, with heart rates up to 1260 beats per minute, breathing rate of about 250 breaths per minute even at rest, and oxygen consumption of about 4 ml oxygen/g/hour at rest. During flight, hummingbird oxygen consumption per gram of muscle tissue is approximately 10 times higher than that seen for elite human athletes.+ — Wikipedia.