The nest of an eastern phoebe with four phoebe eggs and one cowbird egg.

My phoebes hate me. I can’t say I blame them. It’s been a tough year.

Eastern phoebes love to nest under cover. Is there a porch, outhouse, or trailhead kiosk in Maine that doesn’t have a pair nesting under the roofline? My pair is nesting beneath the eaves of the garage for the first time.

Usually they nest on the porch.

It was a short winter, but a dry spring. Insect life was a little meager earlier this year, and some of the insectivores appeared to be food-challenged. My phoebes seemed to be getting a slow start on egg-laying. They were attentive to the nest, but not sitting on it much.  

So I checked. I stood on a stool, and held a mirror over their nest, just long enough to peek. There was an egg. No, wait, two eggs. Oh, NO! One of them was a cowbird egg!

Brown-headed cowbirds are brood parasites. They lay their eggs in the nests of other birds, to be raised by unwitting foster parents. One credible hypothesis for this behavior is that they had no choice. They evolved to follow bison herds, feasting on the flies attracted to them. Consequently, the cowbirds could not count on remaining in one place long enough to raise a family.

Phoebe eggs are small and white. Cowbird eggs are larger and mottled brown. It was immediately obvious that my phoebes had been victimized. Frankly, phoebes aren’t very subtle about hiding their nests, making themselves an easy target for cowbirds. Many other songbirds are victimized as well, but some species have wised up. Some now recognize an egg that’s not their own, and may re-nest. A few even build another nest layer on top of the invader, and try again.

Phoebes aren’t that clever. The bigger cowbird egg hatches sooner, producing a bigger baby. The chick squirms a lot, often pushing the other eggs out of the nest, or even the other nestlings. The result was inevitable. My phoebes would successfully raise a cowbird, but lose their own offspring.

My first instinct was revulsion. I pondered removing the offending egg. What was the ethical thing to do? I turned to the internet for advice, and a consensus emerged. I should let nature take its course. Cowbirds may be parasites, but they deserve life, too. While that may be a noble ethic, my benign attitude toward parasites might be different if I had a tapeworm.

I resolved to watch developments over the ensuing weeks. Sure enough, the cowbird hatched five days before the others. By the time all four phoebes were out of the shell, their step-sibling was three times their size, and demanding all the food. Within a week, the cowbird was nearly ready to fly, while the underfed phoebes were scrawny and featherless. It was only a matter of time before there would be only one nestling alive.

Or so I thought.

Something dramatic happened. While I was away for a couple of days, the cowbird and two of the phoebe chicks disappeared. Perhaps the cowbird had fledged, and fluttered off the nest. If so, I would expect the two parents to keep tending it until it was old enough to forage on its own. But they didn’t. They cared solely for the two remaining chicks. Perhaps a predator – most likely a red squirrel — had found the nest and carried off the cowbird and two of the phoebe chicks before the parents could chase it off. But if so, I would expect the nest to be damaged, and it wasn’t. Perhaps the cowbird had grown so large that it had pushed two victims from the nest, before prematurely fluttering off to its own demise. I’ll never know.

Whatever misfortune had befallen the others, the surviving phoebe chicks benefited greatly. Now that there were only two hungry mouths to feed, and two parents to feed them, the previously malnourished chicks grew rapidly. The proud parents had snatched partial breeding success from almost certain failure. Nature had taken its course.

Still, my phoebes hated me. Even though I kept a respectful distance (most of the time), all of my abnormal, unwanted nest-peeping had made them deeply suspicious. In previous years, they had barely sounded the alarm when I was in the yard. Now, they were yelling loud “cheeps” as soon as they heard the front door open. I had to remind them, “Hey, this is my house, too, you know!”

I hope we’ll all have less drama next year.

Bob Duchesne, Good Birding

Bob Duchesne serves as vice president of Maine Audubon’s Penobscot Valley Chapter. He developed the Maine Birding Trail, with information at mainebirdingtrail.com. He can be reached at duchesne@midmaine.com.