I anxiously await the arrival of the ruby-throated hummingbirds each
year around the first week of May, as this, along with the
daffodils, is a sure sign of spring. Knowing a few facts about these
unique birds helps me, and may help you, appreciate them
even more.
Although there are over 300 species of hummingbirds in the world, only
about 16 migrate each year to North America, and
only one--the Ruby-throated-- nests east of the Mississippi River.
Rubythroats overwinter in Mexico and Central America,
beginning their migration north in late winter. They fly alone during
the day, males and females separately, with the males arriving
a week or two before the females. Hummingbirds begin their migration
back south sometime in September, earlier in colder
areas.
As with many birds, the males are the showier of the two genders, having
ruby red throats. Young males don't have this red
coloring, nor do the females that they resemble.
Although they fly on average about 50 miles per hour (compared to 20
miles per hour for barn swallows), they fly faster with
the wind and when migrating. When in flight, males beat their wings
about 70 times per second, females about 53 times per
second (compared to 4.3 times per second for starlings). Another interesting
fact is that due to their wing structure, these are
the only birds that can fly in any direction, even backwards!
Rubythroats are about three and one half inches long and weigh about
a tenth of an ounce--less than a penny. Their breast
muscles make up 25 percent of their body weight (compared to five percent
for humans). Their little hearts (although largest
proportionately to their body of any bird) beat 600 times per minute
and up to 1,200 times during exertion (compared to 200
for most birds and 72 for humans).
As you might imagine from all this exertion, they need lots of energy,
and in fact must feed all day, at least once every 10
minutes. Each feeding is only a half to full minute. Contrary to popular
belief, they lick, not suck, nectar from flowers. Their
grooved tongue is forked and licks about three times per second. They
also eat insects, which provide a good source of protein
and fat.
If severe weather or a food shortage, they can enter a state of "torpor"
in which their heart rate drops drastically, as does their
breathing and body temperature, in order to conserve energy. They can
stay in this state for only eight to 14 hours.
Males are aggressive in protecting their territory, an area about one
quarter acre in size containing nectar sources. As the
sources change with the seasons, their territory also will change.
Hummingbirds basically live alone, the males and females being
together only during courtship and mating.
Unusual flight patterns, such as two birds going up and down alternately
or, more commonly, one bird making a U-shaped arc
back and forth can indicate aggression, protection of territory, or
courtship. The actions often depend on whether the birds are
both male or a male and a female.
If the courtship is successful, the female makes a nest the size of
a large thimble. She starts with the scales protecting tree buds,
then covers the outside of the nest with lichens and the inside with
plant fluff such as from leaves and seeds. She lays only two
or three eggs, which take about two weeks to incubate. The fledglings
remain in the nest from two to four weeks.
Hummingbirds may live 12 years, but the average life span is three to
five years. Although the greatest losses are from their long
migration, the biggest threat is loss of habitat, either in their overwintering
or summer areas. You can help by providing plenty of
the flowers and other aspects conducive to their summer residence in
the North. They are especially attracted to red
nectar-producing flowers, and to a lesser degree pink, rose, purple,
and orange. Favorite plants include bee balm, hollyhocks,
verbena, and phlox, among others.
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University of Vermont
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