September 2010 Migration Through Southern Ontario

Details on the monarch's migration this fall in southern Ontario

(Ontario, Canada) Monarch enthusiasts learned in January 2010 that the 2009 overwintering monarch population in Mexico was the lowest ever recorded – 1.92 hectares. In February 2010, the Monarch Butterfly Biosphere Reserve experienced severe torrential rains followed by snow and freezing temperatures that negatively impacted the overwintering monarchs. Many of us were uncertain about what recovery the monarch population would make in 2010.

The first signs of the southern monarch migration in southern Ontario were noted in early August.  Residents in the northern breeding range also reported that the population this year was “remarkably better”, while southern Ontario residents were reporting larger numbers of monarchs in urban flower gardens. About August 19th, observers in some areas reported small clusters of monarchs forming on cool nights and by August 25th, observers noted good numbers of adult monarchs feeding on goldenrod and other flowering plants along the north shores of Lake Ontario and Erie. While some nights were quite cool, approaching 50 F, daytime temperatures on September 1st in the Toronto area were in excess of 89 F.

The first report of clustering monarchs came on September 5th, when 1000 to 2000 monarchs were discovered roosting on willow trees near Frenchman’s Bay and the Pickering Nuclear Power Plant east of Toronto. On September 8th,  one observer reported seeing hundreds of monarchs feeding on wild flowers and in clover fields in eastern Ontario and also in western Quebec. On the evening of September 9th, an estimated 10,000 monarch butterflies roosted for the night at Presqu’ile Provincial Park near Brighton, Ontario. Further reports trickled in for that date, with 10,000 to 15,000 estimated at Port Burwell and Monarch Landing west of Long Point on Lake Erie; the Hawk Cliff Hawkwatch at Port Stanley on Lake Erie reported that during 3 hours up to 100 to 130 monarchs per minute were counted passing by the cliff. Numerous other reports of monarchs streaming by or clustering in large numbers were reported from many locations on the north shores of Lakes Ontario and Erie.

On September 12th, several hundred were found roosting on one tree on the Leslie Street Spit in Toronto, while 15,000 were estimated at the tip of Point Pelee National Park and another five to seven thousand passing through the Walpole Island First Nations on the Canadian side of Lake St. Clair north of Detroit. While September 15th was wet at times and temperatures at noon only 53 F, several hundred monarchs were reported along the beaches and lake shore trails at Presqu’ile Provincial Park. September 16th was a warm day and thousands and thousands of monarchs were migrating west through Toronto’s Leslie Street Spit, stopping to feed on the abundant goldenrod, while thousands were reportedly flying past the Hawk Cliff Hawkwatch. A cluster of about 8,000 monarchs was discovered on September 17th just east of Port Alma on the north shore of Lake Erie between Rondeau Provincial Park and Point Pelee National Park.  On September 18th, many hundreds of monarchs were reportedly passing by the Cranberry Hawkwatch at Whitby while at the lighthouse at the tip of Toronto’s Leslie Street Spit, an observer was surprised to see thousands of monarchs feeding and migrating on what was a dull, overcast day.  On September 20th, one observer estimated 5000 monarchs streaming past as he walked north along the west beach of Point Pelee National Park.

On September 22nd, in advance of a cold front and rains, there was a strong migration of monarchs along the north shore of Lake Ontario. At Cranberry Marsh Hawk Watch at Whitby, one observer wrote: “It was perhaps the best Monarch flight I think I've ever seen with many hundreds (thousands?) of them going though. At most times all through the observation period, 30-50 were in view as they streamed westward”. While no monarchs were counted at the tip of Point Pelee the previous night, 1,100 were counted on September 22nd, and only 2 on September 23rd

With the approach of cooler wetter days and nights, it was thought that the bulk of the migration had passed through Ontario. On September 27th, temperatures warmed up in the afternoon and good numbers of monarchs were reported at key locations across the province. At Toronto, dozens of very fresh monarchs were feeding almost exclusively on New England asters.  

It is now mid October 2010 in Ontario. Leaves are falling off of the deciduous trees and night temperatures have dropped below freezing in many localities. Late monarchs are still being reported on warm days and this trend may continue into November. We hope that these observations indicate that the monarchs had a successful year of reproduction in central Canada and that this will result in an increase in the size of the overwintering population in Mexico.

We have also posted a map of the monarch sightings in southern Canada, a photograph at Pain Court Ontario, and another at the Pickering Nuclear Power Plant and two You Tube videos, one at Presqu’ile Provincial Park and the other at near Port Alma on Lake Erie.

--Don Davis. MBF Board of Directors