Hummingbirds
DB: This is Earth and Sky. Curtis Dunsmore of Frederick, Maryland writes, “Hi, I’d like to know why hummingbirds are so territorial and why they fly to Mexico in late summer.”
JB: Curtis, the champion migrant among hummingbirds is the rufous hummingbird. This species makes a yearly trip between wintering grounds in Mexico and breeding grounds in the U.S. Pacific Northwest and Alaska. But it’s not so much that these hummingbirds fly south in the summer as that they fly north in the spring. Hummingbirds are tropical birds, but some head north in the spring – to areas where insects are super-abundant – such as Alaska.
DB: A migrating rufous hummingbird has to make several “pit stops” to rest and refuel. At each “stopover site,” a bird claims a plot of nectar-filled flowers and guards it for a few days – chasing away other birds, butterflies and bees. Hummingbirds have to defend their territories furiously because it really is a matter of life and death. With their small size and high metabolism, they can’t really pack on a layer of fat. Instead, they have to find and claim a reliable food source.
JB: They’re so possessive that – early in the morning, when they start feeding – they drain the nectar from flowers at the edge of their territories first – to foil any competitor who might try to sneak a drink on the outskirts.
DB: Today’s program was made possible by the National Fish and Wildlife Foundation, in cooperation with the U.S. Forest Service. We’re Block and Byrd for Earth and Sky.
The following individuals were interviewed for today’s show. Our thanks to:
Keith Graves
District Ranger
Nogales Ranger District
Nogales, AZ
Sheri Williamson
Director and Naturalist
Southeastern Arizona Bird Observatory
Bisbee, AZ
More Resources:
Carpenter, F.L., D.C. Paton, and M.A. Hixon. 1983. Weight gain and adjustment of feeding territory size in migrant hummingbirds. Proc. Nat. Acad. Sci. U.S.A. 80:7259-7263.
Calder, W.A. 1993. Rufous hummingbird (Selasphorus rufus). In A. Poole and F. Gill, editors. The Birds of North America, No. 53. Philadelphia: Academy of Natural Sciences and American Ornithologists’ Union.
Hummingbird Migration (Maintained by Larry and Terrie Gates of Portal, AZ.)
Rufous Hummingbird (Natural history information about rufous hummingbirds on the web site of the Hummer/Bird Study Group)
Southeastern Arizona Bird Observatory
Author’s notes:
Rufuous hummingbirds seem to know just how much fuel they need to feed their tiny bodies. In one study of rufous hummingbird territorial behavior, scientists established where the boundaries of each birds’ territory lay, then covered half the flowers in each territory with cloth, so the birds couldn’t drink. In response, the birds increased their territory size. It seems that each bird can somehow tell how much nectar is in the patch that it controls, and adjusts the boundaries accordingly. As further evidence, the scientists also rigged a tiny scale on the branch that each territory holder used for a perch. In this way, they could assess the bird’s weight each time it alighted after a feeding bout. The researchers found that hummingbirds adjusted the size of the territory to maximize their daily weight gain.
If you want to attract hummingbirds to your yard, plant red flowers such as bee balm, or hang up a sugar-water-filled hummingbird feeder. Contrary to popular belief, you don’t need to worry that leaving your feeders up in the fall will prevent hummingbirds from migrating. The instinctive urge to migrate is so strong that it would take much more than a free meal to keep a healthy bird from heading south. Though most rufous hummingbirds overwinter in Mexico, the population of birds overwintering within the southeastern United States (especially Louisiana) seems to be growing. Scientists think that a small number of birds wander off course each year; birds that ended up around New Orleans and Baton Rouge found a welcoming winter home where yards were blooming with flowers and hummingbird feeders were kept filled. So their numbers seem to be growing.
Additional Teacher Resources
USGS Northern Prairie Wildlife Research Center: Forest and Rangeland Birds of the United States- Rufous Hummingbird, Selasphorus rufus
A report on the natural history and habitat use of the Rufous Hummingbird.
Forest Preserve District of Cook County, Illinois: Hummingbirds
A broad overview of the natural history, migratory patterns, variety of species, and behavioral patterns of hummingbirds found in the United States.
California Dept. of Fish & Game and California Interagency Wildlife Task Group: Rufous Hummingbird- Selasphorus rufus
A more scientific publication covering the distribution, abundance, habitat requirements, life history and territory of the Rufous Hummingbird.
U.S. Forest Service, Deschutes & Ochoco National Forests and Crooked River National Grasslands: Non-Perching Land Birds-hummingbirds
Several species of migratory hummingbirds occur in central Oregon. Hummingbirds are the smallest North American bird; these tiny birds are often seen hovering while they use their long tubular bills to draw nectar from flowers. Many are attracted to nectar filled feeders; hummingbirds are extremely territorial, and create quite a spectacle at feeders. This publication gives brief scientific descriptions of several species of hummingbird including the Rufous Hummingbird.
