Wednesday, May 6, 2015

I don't know that sound!

Lake Erie Bluffs. It’s a large park in eastern Lake County  - 600 acres - and its name describes its location. What the name doesn’t tell you is how much diverse habitat is available for many species of birds. I noticed last year that butterflies were abundant, including some that did not look familiar to me, and I’m sure I’m going to find a lot of singing insects when I look more closely there in later summer this year.

Right now, though, my focus is on the birds. They move north through Ohio, arrive at Lake Erie, and wait for the wind to turn out of the south to help them across. When the wind is northerly, the birds that have arrived stay where they are until traveling conditions improve. 

This past Saturday (May 2nd), I went with my friend Lisle to search the extensive shrubby areas and fields for Yellow Warbler, Brown Thrashers, White-throated and White-crowned Sparrows, and perhaps the first Catbirds. Birds were singing and calling everywhere! 

But closer to the lake, I heard something I did not recognize. Lisle heard it, too. It seemed to be coming from near the path down from the bluffs to the lake edge. We had to go find out, of course. 

The sounds reminded us of something like a Green or Great Blue Heron, but all we saw were some Bonaparte’s Gulls and Red-breasted Mergansers. From a distance, the black heads of the gulls seemed more like these birds could be terns, but I knew that Bonaparte’s Gulls have black heads when they’re in their breeding plumage. That in itself was splendid, as I’d only seem them in their winter white. 

But who was making those creaky, croaking, guttural sounds? I hadn’t heard Bonaparte’s Gulls make that sound in the winter, yet the noise seemed to be coming from their direction. 

It was the Bonaparte’s Gulls! 

Some of you know gulls much better than I do, but I'm going to guess that many of you are not too familiar with the small, beautiful Bonaparte's Gull. Let’s take a look at this interesting species and especially at their calls. 

Bonaparte’s Gulls can be found on Lake Erie in late autumn until the lake freezes. They return as Lake Erie begins to thaw during their migration north to the boreal forest. 

In their northern breeding territory, they actually build nests in trees near lakes and eat insects. It’s rather like they live two very different lives depending on the time of year.

You won’t find them dining with our ever-present Ring-billed Gulls in parking lots and landfills. They do eat fish when they’re here on Lake Erie, though, and that’s exactly what they were doing. There was an abundance of small fish right near the shore, and word spread quickly.

First there was a small group, then more joined them. The activity became more frantic as their number increased. 

Here’s the curious thing about their calls. They sound like they are lower in pitch than the calls of our common gulls. Actually, the opposite is true. 

Look at the sonogram below. Do you see those little lines and dots that are lower, lining up at 1000 to 1500 Hz? (I think you'll be able to hear them in the background.) Those sound like they have pitch to us and we'll probably perceive them as somewhat musical. 

Those grating, guttural calls of the Bonaparte’s Gulls look brighter and more prominent because the birds were closer, but notice they are also higher. They begin where the other gulls left off – at about 1500 Hz, and go up to about 4000 Hz. (For you musicians, there appear to be overtones that are considerably higher.) The range and complexity make those calls sound less musical. 

My priority was recording, as this was a new sound for me and I had no idea when I might hear it again. I was able to get a few photos before they drifted farther up the shoreline, but soon they were too far away. 

If Lisle and I hadn’t followed our ears, we would not have learned who was making those strange sounds, seen Bonaparte’s Gulls in their stunning breeding plumage, or observed the feeding frenzy. I probably would not have read about the interesting life history of Bonaparte’s Gulls, either. 

I never thought I’d get around to listening to the specifics of gull calls, but Lake Erie Bluffs brought the possibility to my attention. Maybe next November...

1 comment:

  1. Great post, Lisa. Interesting observation about the overtones, makes them somewhat insect-buzz-like. Beautiful photos, too. Regards, Carl