A fledgling story takes a strange twist
Our Phoebes gave birth to little a little Phoebe, or so we thought.
I mentioned in a recent newsletter that we’ve been hosting a Phoebe family and that their chick seemed to be preparing to set flight from the nest. Within hours, it did just that and then the story took a strange turn. The fledgling made its way down from the nest to a perennial border about 20 feet away and nestled itself among the leaves and shade.
As it turns out my wife Katie about an hour earlier had sent a picture of the chick raising its head high above in its nest to Ben Nickley, the executive director of the Berkshire Bird Observatory. Ben’s an expert birder and wonderful person who’s been leading us and others on bird walks all spring. (If you love birds follow their Instagram account.)
“Our single baby Phoebe is getting ready to go?” Katie asked.
“Darn,” Ben replied. “Looks like a cowbird (neutral-face emoji)”
We knew the birds that built the nest were Eastern Phoebes. They’re light grey with dark heads, part of the flycatcher family. The Brown-headed cowbird is larger and darker. It also, we have now discovered, is a parasitic bird with a nasty habit of laying eggs in the nests of other birds. Phoebes, it seems, are frequent victims.
The unsuspecting parents then sit on a cowbird egg along with theirs as if it's their own. Cowbird chicks are much bigger than Phoebe chicks and are born much earlier. They’re also monstrous in size compared to a Phoebe chick. Our Phoebes are now exhausting themselves bringing insects to the cowbird fledgling in our garden believing, for all we know, it is one of their own.
We’re hoping the Phoebes haven’t forgotten their own chicks, which sometimes happen when they’ve unwittingly adopted a cowbird. We were encouraged last night when one of them was sitting on the nest again. Today, sadly, the nest seems quiet.
So what’s up with cowbirds?
“Cowbirds, Everybody’s Favorite Villain,” is the headline of a story posted a few years ago on the Southern Wisconsin Bird Alliance website.
“A lot of people really dislike – even hate – cowbirds,” begins the ultimately sympathetic piece. “It can be hard to watch a small warbler trying to keep a huge cowbird chick fed, and it’s sad when host species eggs get destroyed.”
Needless to say, the past 24 hours have offered us a crash course in cowbird behavior and exposed us to the strange reproduction habits of obligate brood parasites. These are birds that lay eggs in nests of other species, having lost the ability to build nests and incubate eggs on their own. It’s estimated that 1 percent of all bird species are obligate brood parasites, including, in addition to cowbirds, about half of all cukoos and all Black-headed Ducks in South America.
Cowbirds are crafty. They scout for potential nest hosts for their offspring and time their mating so they can swoop in when the nest is unoccupied and quickly lay an egg before leaving the scene. If all goes well, the host parents will accept the egg even if it’s often a different color and, in many cases, slightly larger than their own.
Cowbird eggs hatch more quickly and, once born, the chicks grow more rapidly than those of many other birds. “The host parents will try to feed both the chicks in the nest and those that have fledged, but they tend to give preference to the ones who are already out in the world,” the Southern Wisconsin Bird Alliance said, adding: “Another win for the cowbird chick.”
The Bird Alliance story, which is worth reading if you’re interested in learning more, notes that cowbirds originally hung around American bison, moving with the herds through the Central Plains. After one season their parasitism wouldn’t affect native bird host populations since they would move on with the herd. Nowadays, though, they lack a native habitat of their own, which means they can become more of a nuisance to local birds.
We’re just waiting to see how the Phoebe chicks fare, if they’re still with us, while simultaneously making sure our dogs stay clear of the cowbird fledgling – the chicks’ adopted sibling – until it learns to fly. It’s been keeping us busy, though nothing like the two Phoebes, male and female, who mate for life.
Headline: Fake Fledgling Fools Fraught Phoebe Family
Cowbirds can also be entertaining as they teach their fledglings to fly.