Canada's butterfly migration is largest on record
300 million red admiral butterflies estimated from Windsor to New Brunswick
Butterflieshave migrated acrossEastern Canada this spring inunprecedented numbers, reflecting the warm winter throughout North America andraising alarm bells about whatit might mean for other species.
"It's probably the most exciting year for butterflies that Canada has ever seen," said Jeremy Kerr, a professor of biology at the University of Ottawa.
Estimates from the field suggest there are 300 million red admiral butterflies from Windsor to New Brunswickmore than 10 times what would be seen in a typical year. Numerous other butterfly specieshave also arrived or appearedingreater numbers, Kerr said.
What are red admirals?
Red admiral butterflies, Vanessa atalanta, are found throughout North America. Smaller than a monarch, their black, orange (some say red)and white wings are between about 4.5 and5.7 centimetres wide.Red admiralsare extremely adaptable and can sip nectar from almost any kind of flower. They are often seen in gardens.
The explosion in butterfly populations is mostly due to the warm weather this winter throughout North America. It caused butterflies to emerge from their overwintering forms in places like Texas and Florida sooner, and then improved their survival rates as they headed north.
The first local butterflies (ones that overwinter in Canada)were seenas early as March"damned peculiar," Kerr saidand southern Ontario was hit by itsfirst big wave of migratory butterflies in mid-April,thanks in part tostrong winds. The red admirals moved so far north so early that they flew into areas with snow, something that normally wouldn't happen.
They were also joined by the painted lady, a closely related butterfly.
A second wave arrived in early May, boosting the diversity in southern Ontario, especiallyfromWindsor to Toronto.Kerr saidoneenthusiast recorded 22 different species in a single Windsorpark.The blog of the Royal Ontario Museum in Toronto notedthe appearance of such speciesas the American lady, question mark, mourning cloak, cloudless sulphur, grey hairstreak, variegated fritillary and American snout.
How do you count butterflies?
Researchers take a best guess based on reports from the field, surveying particular sites and extrapolating a larger number from the count. For instance, Kerr recently surveyed a 100-metre wide location for red admirals, counting 102 flying overhead in an hour. Biologists collect such information from scientists and enthusiasts to keep track of the leading edge of migrations and how many butterflies are likely involved. This year, the University of Ottawa started an "eButterfly" hub that allows"citizen scientists"to post their observations and photographs.
Felix Sperling, a biologist atthe University of Alberta, said the earlyand large migration has been a strictly eastern phenonemon, save for some red admirals approaching the southern border of Manitoba.He said the red admiral is known to have surges and years where they're no-showsbut in Western Canada they tend to have their own ebbs and flows in numbers.
Kerr said the butterflies won't have any immediate effect on their environmentthe bigger question is what it might mean for other animals.
Butterflies are excellent indicators of environmental changes."Is it a really beautiful sign of something really worrying to come?"
However, Sperling and Kerr both said it's impossible to know what the change means.
"We don't know yet which species are going to be winners and which are going to be losers in this time of rapid environmental change," Kerr said.
Two immediate questions yet to be answered arehow abundantmonarch butterflies will be when they arrive (usually in early to mid-June), and how plentiful the red admirals (and their larvae)will be when they give birth to asecond generation this summer.
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