How Do They Know?

Rose-breasted Grosbeak

It's a source of wonder to me how regular and predictable migrating birds can be. We've lived in this house for five years and I've kept desultory notes on the comings and goings of the bird life around us for all this time. The data I've gathered (such as they are) give me some sense of what (or who) to expect, and when.

Each year I eagerly look forward to the first week in May--i.e., now!--as this is the time when Spring migrants really begin to arrive. Not only is it cool simply to have some new birds to look at, but those who typically show up during this period are among the most colorful birds we see all year. Rose-breasted Grosbeaks, Indigo Buntings, warblers of various sorts, Ruby-throated Hummingbirds, Baltimore Orioles, and Scarlet Tanagers--each species brings its own special brand of bling to the table. There are often times during the winter when the bird life in the yard seems like an avian take on of Fifty Shades of Grey. Although the chickadees, titmice, nuthatches, Hairy & Downy Woodpeckers, and juncos look stately and elegant, colorful they are not. Our pair of more-or-less-resident cardinals provides virtually the only spark of color among the birds of a Maine winter.

We moved into this house permanently in late April, 2010. Because we had to deal with the chaos of unpacking and setting things up, my bird notes for that first Spring are pretty sketchy. I did note, however, that by May 10 we had Baltimore Orioles, Rose-breasted Grosbeaks, and Scarlet Tanagers in the yard. The first Indigo Bunting showed up the following day. I have no notes on hummingbirds--we probably did not hang feeders until a bit later--but we had had a warbler species or two by the time I made my first records. In 2011, the grosbeaks, orioles, buntings, and hummers, plus a single Black-and-white Warbler, all made their first appearance on May 4. A couple of Grey Catbirds had already been around for a few days that year.
 

Indigo Bunting

In 2012 it was again on May 4th when I saw the first Rose-breasted Grosbeak, together with a couple of warblers. Two days later the orioles graced us with their presence, while the first buntings and hummingbirds did not arrive until the 8th.

The colorful returnees were a bit tardier the following year; my notes tell me that it was not until May 11, 2013 that I saw the year's first grosbeak, and May 12th the first oriole. Last year the first grosbeak was a bit more prompt, showing up on May 3rd. I apparently failed to note the arrival of the first oriole of the year but a pair of Scarlet Tanagers was here, happily feeding on my suet, by May 12th.

Scarlet Tanager

So, here it is, May 4th (aka Star Wars Day) and things are right on schedule. This morning when I looked out of my office window into the woods, the first bird I saw was a Black-throated Blue Warbler! Upon going outside with binoculars for a better look, I saw that he was accompanied by a Yellow-rump. A bit later in the day a Black-and-white was busily skittering up and down tree trunks. Around 1:15 a male Rose-breasted Grosbeak was pigging out on sunflower seed in the window feeder. Earlier in the day I'd made up a batch of nectar for hummingbirds. I hung out the first feeder about the time I saw the grosbeak and had a customer within 15 minutes. I also put out an orange half for the orioles but so far it's gone unsampled.

I look forward to celebrating the return of more of our avian prodigals in the next few days. The Indigo Buntings and Scarlet Tanagers should be along soon, as well as many more species of warblers. It's a bit surprising that catbirds have yet to show themselves but they'll surely be here soon. The best part of having all these guys come through now is that the trees are just beginning to bud out. For the next couple of weeks our ability to spot and identify tiny birds bopping around in the treetops is as good as it's ever going to be.

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I will again ask the question that I posed in the title to this post: how do migrating birds manage to keep to a schedule that is, if not exactly precise, at least predictable within a fairly small range of deviation? Ornithologists have devoted a good deal of time and attention in an effort to come up with an explanation for this and other mysteries surrounding bird migration.

Frankly, I don't really want to know, at least not on a technical level. I don't want to trouble myself with matters of migration triggers, or shifting seasonal resources, or trying to calculate the air speed velocity of an unladen swallow (either African or European!). While it's wonderful that there are intelligent people in the world who work long and hard to understand the whys and wherefores of such things, I prefer to let my question stand as a rhetorical one. It is simply enough to know that the birds will be back around the same time next year, when they will again brighten both the visual and aural environment around our house. In the words of Iris DeMent (singing about larger metaphysical issues), I'm content to let the mystery be.

Photos (all of male birds) taken May 12, 2014.