Monarch Fall Roost

Date: 08/17/2010

Number: 15000

September 12
Monarch migration continues here at Point Pelee and a roost of 15,000 on Sunday 12th September is the largest roost we have had since 2003. This year has been an excellent year for butterflies of all species with an early warm spring and twice as many warm days than normal and twice as much rain through June and July compared to long term normals. Quite possibly, with an early start to the reproductive cycle and the extra warmth, Monarchs were able to squeeze in an extra generation at the end of their reproductive season to give us this fabulous migration.

September 6
Cold overnight temperatures of 10 degrees centigrade on the 5th and 6th of September stimulated a movement southwards of monarch butterflies, bringing us our second wave of monarchs on migration. In mid-August, a cold snap brought us monarchs that were nectaring in our immediate area, resulting in a roost of 300 monarchs. Now, we are receiving monarchs from a much larger area north of us, being funnelled to us and concentrated by the Great Lakes.

Despite strong winds from the south and west, monarchs were able to enter the point by flying in the protection of the bushes and trees on land. However, once they reach the southern tip of Point Pelee, they have 40 kilometres of open Lake Erie with nothing to hide behind. So, we began with a roost of 300 on the night of the 6th, and numbers accumulated to a count of 8,000 by Thursday night the 9th of September. The following morning, with the warmth of the sun and a gentle 5 km/hr breeze from the north, monarchs began flying off the tip of Point Pelee at 8 o'clock at a rate of 60 butterflies per minute in a southwesterly direction towards Mexico. At this rate, most of them had left the point by 10 o'clock in the morning.

We were happy to see them off safely on a calm morning, knowing they would reach Ohio in about an hour and a half.

August 17
A sharp drop in overnight temperatures here at Point Pelee on the 15th and 16th of August brought us a roost of 300 Monarch butterflies at the tip of Point Pelee on the 17th, about two weeks earlier than normal. However, temperatures have warmed up and we will be waiting patiently for another cold night or strong winds from the north before we see any further movement southwards.

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Leamington, ON

Latitude: 42 Longitude: -82.5

Observed by: John
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