. INCREDIBLE BUTTERFLY NAVIGATION: Monarch butterflies find their way thousands of miles to specific mountains
Millions of monarch butterflies, pictured, migrate 2,000 miles every
year. In 1976, zoologists found them at the top of the ‘Mountain of
Butterflies’ in Mexico. While scientists know the monarchs target 12 to
15 Mexican mountain sites, they don’t know how they navigate there
Each year, millions of North American monarch butterflies migrate 2,000
miles south for winter. For years, no one knew where they ended up.
Then, in the 1950s, Norah Urquhart and her husband Fred, a zoologist,
began tagging and tracking the creatures. In 1976, tipped off by a local
woodcutter, they climbed to the top of the ‘Mountain of Butterflies’.
All the butterflies in North America, it seemed, were in a mountain
forest in Mexico.
That’s not where the story ends. While we know the monarchs target just
12 to 15 Mexican mountain sites, we don’t know how they navigate there.
Studies suggest they use the position of the Sun to fly south, adjusting
for the time of day through circadian clocks in their antennae. But the
Sun only gives them a general direction. What guides them towards the
Michoacan mountains? ‘They are funnelled in, probably by landmarks as
they reach the overwintering site,’ said Professor Steven Reppert, a
monarch expert at the University of Massachusetts. ‘But how they home in is still a mystery.’
Landmarks such as the Gulf of Mexico couldn’t provide enough information
to take butterflies all the way, so they must use other short-range
navigation systems. One theory is that a geomagnetic force attracts
them, although, says Reppert, ‘that’s never really panned out’.
Scientists only recently acquired some of the genetic tools needed to
probe the details of their navigation systems. Now they have a full
genetic code, they are starting to knock out genes to see how this
affects the animals’ sense of direction.