Scientists and watchers said they had hoped the number butterflies returning north from wintering in Mexico would increase through the generations, but there's no indication this happened, CBC News reported Tuesday.
Only a small number of monarchs made it to Canada during the summer to propagate the generation now migrating to Mexico, and early indications are last year's record lows will be followed by even lower numbers this fall, scientists said.
Elizabeth Howard, founder and director of Journey North, a citizen-scientist organization that tracks migration of monarchs, said one sign of the healthiness of the monarchs is the number of roosts formed in late August and September. Journey North monitors these roosts during migration periods.
"During migration, monarchs form overnight roosts in places like Point Pelee or Long Point [in southern Ontario], where the monarchs are congregating before crossing the Great Lakes, places where people generally see huge overnight clusters of monarchs gathering," Howard said.
Howard told CBC News during the same time period in 2011, Journey North received 55 reports of roosts, but only 25 in 2012. This year, she said, the organization has received only 17 reports.
Monarch numbers have fluctuated dramatically over the years and have trended downward for the past 16 years, the CBC said. After last year's hot spring followed by the drought in the U.S. Midwest, monarch watchers had hoped for a rebound in 2013.