Observations on Hummingbirds

For two years, I was involved as a volunteer with the Hummingbird Project run by the University of Arizona. My job was to identify hummers, observe and record their behavior at the feeders in my yard. Over that time I was able to recognize individual birds of the same species, since each has a slight variation from the ideal pictured in a bird book. Hummers have good memories. They can return to a feeder year after year.

Hummingbirds are ferocious. The males jealously guard feeders and flowers. Females guard nesting sites. I’ve seen one Rufous male literally drive another hummingbird into the ground and jab him with his sharp beak. They have a variety of vocalizations including a “war cry,” a buzzing to warn others away. The Rufous is particularly pugnacious, but one posed long enough for me to take his picture, as he sat watching over his territory.

Rufous, natureHummingbirds live on the edge. Their small size and ability to fly forwards, backwards, upside down, and hover, requires a racing metabolism. At rest, their hearts beat 500 times per minute and this increases to over 1,200 beats per minute during flight. Their wings beat 80 times per second; body temperature is 105- to 109 F.

To function, a hummingbird must consume 70% of its body weight in solid food per day (8-12 calories) and 4- to 8 times its body weight in water. They consume flower nectar (and sugar water), insects, and spiders, as well as tree sap in some areas. They can completely digest sucrose within 20 minutes. According to the Peterson Field Guide, “Despite the predominance of certain hues in hummingbird pollinated flowers, color is far less important… than the quantity and quality of the nectar.

When presented with a variety of flowers, hummingbirds will maximize their energy intake by selecting for highest nectar output and richest concentration of sugars, regardless of flower shape or color. Taste also ranks above flower color…” Hummers prefer sucrose over other sugars such as glucose and fructose.

To take in the oxygen they need to burn food, hummers respire at the rate of 300 breaths per minute, even at rest. An excited hummer can breathe twice as fast. Hummers, which are the smallest warm-blooded vertebrates, have the largest heart-to-body ratio of any warm-blooded vertebrate, and the largest brain-to-body ratio of any bird.

They need that relatively big brain for their split-second aerial maneuvering. Hummers are the only birds that gain lift from both the downstroke and upstroke of their wings. The wing motion describes a horizontal figure eight. After the downstroke, the wing is turned over at the shoulder so that the up stroke becomes another downstroke.

There are over 300 species, all in the western hemisphere, and they range from the tip of South America to Alaska. There are 17 species native to the Sonoran Desert Region. Hummers in our region range in length from 2.75 inches to 5.25 inches and weigh 2 to 10 grams (0.07 to 0.35 ounces). Only two hummingbirds, the Ruby Throat and the Rufus, occur regularly east of the Mississippi River in the U.S.

Most hummers in our region exhibit some migratory behavior. The champion is the Rufous which travels from Mexico to Alaska and back every year. Second is the Ruby Throat which migrates from the eastern U.S. to Mexico. Some travel along the coast, but others take a 13-hour, non-stop flight across the Gulf of Mexico. Those long-distance flyers try to double their body weight for fuel before the trip. Normal flight speed is 25- to 30 mph, but they can do bursts of 60 mph if necessary.

Hummingbirds are very territorial; both sexes protect feeding territories; males protect courtship territories; and females protect nesting territories. Hummers are promiscuous breeders. The male merely courts and mates with receptive females. The female may mate with several males, but she alone builds the nest, lays and incubates the eggs, and tends the young.

Hummer In Nest1The nest is about two inches in diameter. The female uses plant fiber and moss bound with spider web silk. The nest may be lined with hair or feathers and decorated with leaves, bark strips, or lichens to help camouflage it. Generally, two raisin-sized eggs are laid and incubated for about two weeks. Young fledge about three weeks after hatching, but they hang around momma for a while hoping to get fed.

Hummingbirds are colorful. Most of that color is not produced by pigments as in other birds, but by refraction of light by the feathers. The feathers contain filmy layers that hold granules of melanin and air bubbles, which refract light differently depending on the angle of impingement. The bubbles act as tiny prisms, breaking the light into its component colors.

Where do they go at night, especially in the winter? Hummers are often perilously close to the limits of their energy reserves. On cold nights, when the costs of keeping warm are especially high, it may be too risky for a hummer to maintain its high metabolism. In that case, it will seek shelter of a branch or crevasse, bristle its feathers to let body heat escape, and allow its body temperature to approach that of its surroundings. Its heart rate drops dramatically, and it may stop breathing for minutes at a time. It appears lifeless, clinging motionlessly to its branch with its head drawn close to its body and its bill pointing sharply upward. At daybreak it revs its metabolism and warms itself again. This temporary hibernation is called torpor. Hummingbirds become torpid not only to deal with fuel crises, but also to save energy for migration. And since birds lose moisture with every breath, becoming torpid also helps desert hummers conserve water.

Like many animals in the wild, most hummers don’t survive the first year, but those that do have a life expectancy of three to four years. Some tagged birds in Colorado are known to be 12 years old. One hummer at the Arizona-Sonora Desert Museum was claimed to be 18 years old at death.

If you set up feeders, use 1 part sugar in 4 parts water in the winter, and 1 part sugar in 5 parts water in the summer. Clean the feeders before each filling. Do not use coloring, honey, or artificial sweeteners.

If you want to learn to identify hummingbirds, I recommend “Hummingbirds of North America” a Peterson Field Guide by Sheri L. Williamson. This book contains photos rather than drawings. Photos include close-ups of heads and tails which aid identification. The book also has a good discussion of natural history and good range maps. It covers 31 species. With practice, you can even learn to identify some hummers by their vocalizations. Some species (usually only the males) also have a distinctive “hum” of the wing beats.

Copyrighted by Jonathan DuHamel. Reprint is permitted provided that credit of authorship is provided and linked back to the source.

2 Comments on "Observations on Hummingbirds"

  1. Colt Cassidy | June 30, 2013 at 10:38 am |

    Hummingbirds are quite possibly the most wonderful creatures on planet Earth.

    That, and ladybugs.

  2. It’s December 21st, and a feeder I put out for the first time yesterday was already 1/3 empty by the end of the day! I believe many websites have too limited a winter range for various species in the AZ winter. I am seeing a LOT of species variation at the feeders, and even more around my blooming winter annuals. Perhaps some previously more southern species have learned to make a winter living in the suburbs and foothills around Phoenix through the winter, or perhaps it is a global warming outcome. Be that as it may, I’m going to have to get a new field guide with better range data!

    Most amusing behavior: two sizable, aggressive male hummers that had been squabbling over the feeder all morning joining forces and walloping the daylights out of thrashers and cactus wrens bent on stealing a few sips of nectar. The only birds they leave well alone are the woodpeckers that occasionally visit for nectar.

Comments are closed.