Why Roost?
Roosting behavior may be temperature-driven. When overnight temperatures are warm, monarchs may not roost or aggregate as tightly. Roosting is a known anti-predator strategy at the overwintering sites in Mexico. Cool temperatures paralyze monarchs, making them vulnerable to predators. A roost provides safety in numbers. Perhaps monarchs shift to roosting behavior only when cold overnight temperatures make them vulnerable.
Patty Moss Wainfleet, Ontario September, 2012
![Monarch nectaring on blazing star](//sightings.journeynorth.org/jnorth/images/userfiles/1348634299.jpg)
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