butterflies and ruby-throated hummingbirds have similar migrations even though one is a bird and the other is a butterfly. Both species eat nectar. Both spend the winter south of the United
States border and migrate north in the spring. Both species begin to arrive in the United States in
the month of March, as they return to their breeding grounds in eastern North America. Both species move north as their habitat becomes ready to support their needs.
makes their migrations different? Do differences in flight speeds matter?
Hummingbirds have been clocked flying 60 miles per hour. They can fly across the Gulf of Mexico in only 20 hours! Monarch butterflies only fly about four miles per hour unless the wind carries them faster.
Unlike monarchs, hummingbirds
have more than one source of food. They can eat
insects and sometimes they even eat sap that drips
from holes made in trees by woodpeckers. This means some hummingbirds
can migrate north before flowers bloom and still
find food. Monarchs must wait for flowers to bloom or they will not have food.
The life cycle of each species also affects the pace of its migration. Hummingbirds can complete the entire spring migration
in one generation. In contrast, the monarch's life cycle causes
a delay. The monarchs that overwintered in
Mexico only live until mid-to-late April. They must lay eggs before they die. It takes
about one month for an egg to develop into an adult butterfly. As adults, this generation completes
the migration to the northern breeding grounds.
Spring temperatures also affect both migrations in many ways. Because they are insects, monarchs are cold-blooded and are paralyzed
by cold temperatures. Monarchs cannot fly unless
their flight muscles are at least 55° F. Because they are birds, hummingbirds
are warm-blooded. They can fly in cold temperatures. However, they must use much more energy to keep their bodies warm.