Monarch migration is in full swing. Some of the migrating butterflies from the Northeast travel as far as 3,000 miles to reach their winter destination in the Sierra Madre Mountains of Mexico. In addition to finding sources of nectar along their migration pathways to build their fat reserves Monarchs must also seek shelter at night, roosting on land when it cools down and they can no longer fly.
It appears that roosting is critical for migrating Monarch survival. Just before dark these solitary diurnal migrants gather in clusters called roosts. A roost can consist of just a few butterflies up to thousands clinging to leaves and branches on a single tree. Cedar, fir, and pine are common species of trees used for roosts, but deciduous trees are also used.
Most roosting trees are along a principal flyway, located in a cool, moist area, provide shelter from the wind and are near a source of nectar. Often roosts last for only a night or two but can last a week or two. Monarchs can but do not necessarily use the same resting sites year after year. It’s generally accepted that these roosts are an anti-predation tactic, employing the strategy of safety in numbers. To see a map of documented 2021 roosts, go to Journey North’s site: https://maps.journeynorth.org/map/?map=monarch-roost-fall&year=2021.
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