Every morning for a week before Oct. 9, I stepped out of my front door at 5:15 a.m. and listened. And every morning I heard crickets and nothing more. But when I stepped out on that Thursday, I was greeted by the constant flight calls of dozens of migrating birds as they winged overhead. Weather conditions finally caused myriads of migrants to suddenly resume their flight south in unison.
Many birders have a particular interest when it comes to how they engage in birding. Some may be interested in a particular group of birds, such as hummingbirds, shorebirds or gulls. Some may be more likely to participate in a particular birding activity such as hawk watching, bird banding, photography or chasing rarities. One area of interest that you may not be as familiar with is the identification of nocturnal flight calls among migrating birds.
Many of the migrants passing through our area right now are nocturnal migrants. Surrounded by darkness and navigating via internal compasses, these nighttime travelers keep in touch with each other via unique chips, buzzes and whistles. Researchers have mapped individual species’ calls onto spectrograms, visual representations for a call’s sound frequency and duration. By using a microphone and recording system, birds can be recorded overnight and the species and numbers can be determined at a later date. This can be a useful tool for analyzing bird population numbers, and could prove to be more efficient and economical than capturing birds with mist nets in a banding operation.
That Thursday morning I was able to identify many Swainson’s thrushes by their high-pitched piping notes, reminiscent of sounds made by spring peeper frogs. I also heard a good number of gray-cheeked thrush calls, and I even heard a couple of rose-breasted grosbeaks. I am nowhere near an expert on nocturnal flight calls, but it was great fun listening in.
There will be plenty more mornings when this phenomenon will occur. If you are an early riser, take a few minutes to listen. For more information on migrant bird call spectrograms, and some audio on some species calls, check out http://bit.ly/1Ddm0tR.