Watching a Roost Form

Few people have the chance to watch a roost form. One observer described it this way:

"The air resembled a monarch airport, with butterflies coming in from every direction, floating through the air, checking out various trees, landing, then taking off again. When one monarch approached a cluster, the roosting butterflies flashed their wings. It took from about 7:15 to 7:35 p.m. for them to cluster in the trees, just before dark."