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Comparing
Migrations
Why Do Rufous Hummingbirds
Seem Far Ahead?
It
seems to be a normal year for timing of the migrations. So why do
Rufous hummers move north so much sooner than Ruby-throats
do?
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| Photo:
Deborah Repasz |
First,
let's explore what's different about Rufous hummingbird bodies.
- Rufous
hummingbirds are naturally cold hardy. They typically
overwinter in cooler areas than Ruby-throats do. They often hatch
in cold mountainous areas and spend nights where the temperatures
are often near freezing. Ruby-throats, which overwinter farther
south in warmer climates, are not well adapted to cold temperatures.
- Both
species can enter a state of "torpor" in cold weather,
but Rufous hummers do it more regularly. Their body temperature
lowers, slowing down their breathing and heart rates. In this
way, they conserve energy, which fuels migration.
But
that's only part of the story! >>
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