| Monarch
butterflies and ruby-throated hummingbirds are both migrating north
right now. The two species are similar in many ways! Both species
are long-distance migrants that eat nectar.
Both species overwinter in areas south of the United
States border. Both begin to arrive in the United States during
the month of March. Both species migrate north
to their breeding grounds in the eastern region
of North America. Both species move north as their habitat
becomes ready to support their needs for food, water, shelter, space.
What
makes the migrations different? As this week's migration map shows,
hummingbirds are migrating north more quickly.
Why? Is it because hummingbirds can fly so much
faster? (They have been clocked flying 60 miles per hour.) Is it
because they can fly over water, and cross the
Gulf of Mexico in only 20 hours?
Hummingbirds
have several adaptations that allow them to migrate where spring
temperatures are too cold for monarchs. All birds
are warm-blooded. All insects are cold-blooded.
How does this difference affect their migrations? Monarchs are paralyzed
by cold temperatures; they cannot fly
unless their flight muscles are at least 60 degrees F. Cold temperatures
do not keep hummingbirds from flying.
Hummingbirds
have more than one source of food. They can eat
insects and sometimes even eat sap that drips from
tree holes drilled by other birds. This means hummingbirds can move
ahead of the blooming flowers and still find food.
Monarchs must wait for flowers to bloom or they
will not have food.
The
hummingbird's life cycle also gives hummingbirds
an advantage. The monarch's life cycle causes a
delay. The generation of monarchs who begin the migration from Mexico
lay eggs as they travel. Those adult butterflies
are at the end of their life cycle. Their offspring must complete
the migration but they need time to grow. It takes
about one month for an egg to develop into an adult
butterfly. The hummingbirds can complete the entire spring migration
in one generation.
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