Nocturnal birdcalls reveal an invisible world

Experienced birders will often use a bird’s calls or songs as a means of identification. Most everyone knows that each species has its own unique song, but birdcalls consisting of single note chips, whistles, tweets, tseeps and other sounds are also unique and can be used to identify the bird.

It is helpful to know the sounds a particular bird makes. It eliminates the need to see the bird, sometimes a tough task, unless you really want to get a look at it. It also gives the bird’s location away, which is very helpful if you want to see it.

I stepped outside one day a couple of weeks ago shortly before 6 a.m. and heard what sounded like spring peepers coming from the sky. Spring peepers are tiny frogs that give a high-pitched “peep” in early spring. I knew it wasn’t frogs but was instead the nocturnal call notes of migrating Swainson’s thrushes overhead. This past week I again heard the same sounds, but mixed in were the rougher nocturnal call notes of three other thrushes – wood thrush, gray-cheeked thrush and veery.

I’m not the best at distinguishing nocturnal call notes, but thrushes are among the easiest to differentiate. You can listen to the flight calls of various thrushes and other migrants by visiting http://pjdeye.blogspot.com/2009/02/thrush-calls.html.

You can hear them too. If you are an early riser like me, step outside while it is still dark and listen for a few minutes. If it is a big migration night you may be amazed at how many traveling birds you will hear before dawn. You might hear warblers, sparrows, tanagers, orioles and other migrants.

In some ways listening to nocturnal flight calls can give a better picture of how many birds are passing through and may even help with population estimates. Migrating birds seem to constantly sound off at night. Even simple recording devices can pick up the sounds.

The recordings can then be analyzed at leisure at a later date to determine which conditions are optimum for movement, which species were moving when, or to gauge the presence of rarer species. Information gathered is often more accurate than visual information gathered during the daytime.

This story was originally published September 24, 2015 at 9:24 AM with the headline "Nocturnal birdcalls reveal an invisible world."