For the past few weeks here on Grouse Mountain, if you wandered around late at night, you would have heard a strange cacophony of bird calls and sounds that you never hear in the light of the day.
These are the calls of the nocturnal migrants. Many bird species migrate at night for safety. Predators such as bird's of prey are not active, and because temperatures are cooler, less energy is spent in staying cool during the long demanding flights of migration. It's the equivalent of going for a late evening or early morning job before the heat of the day hits.
As always, there is safety in numbers so many species, or even mixes of species, migrate together and stay in touch through contact calls. Due to poor visibility, contact calls are the best way to stay in touch with your neighboring migrants during the night. Many of these flocks touch down briefly or pass overhead of the local mountains while flying at altitude. This is why we can hear them so clearly on top of Grouse Mountain.
It's an amazing experience to hear a chorus of birds at one o'clock in the morning! Experts study radar images of migration to determine the quantity and timing of migration. Vast flocks of thousands of birds show up as distincts groupings on radar images and allow ornithologists to study this unique phenomena.