http://news.bbc.co.uk/earth/hi/earth_ne ... 481380.stm
"Monarch butterflies that migrate vast distances have grown larger bodies and wings, researchers have discovered.
These "supersized" butterflies have evolved to cope with the demands of long-distance flight.
In contrast, monarchs that live in one place all year have wings that are up to 20% smaller, report scientists in the journal Evolution....."