Monday, July 20, 2015

The Science Behind Fledging Birds

TOS_grouse_fledglingOn a recent afternoon, I saw a baby ruffed grouse about the size of a pin cushion scurry into the bushes. I had the same impulse I did as a 10-year-old when I scooped up a baby blue jay hopping around on a neighbor’s lawn: I wanted to “rescue” it.  Instead, I kept driving, leaving the tiny bird to its fate.

Fledging is perilous for all birds – most won’t survive their first year – but what exactly is that process? Do nestlings know when to leave or do the parents signal when it’s time? Do they all go at once? Will the parents continue to protect and feed them after they have fledged? And what should I have done, if anything, to help that baby ruffed grouse?

For most birds, instinct drives them to depart, said Robyn Bailey, NestWatch Project Leader at the Cornell Lab of Ornithology. “Nestlings begin exercising their flight muscles and standing on the edge of the nest without any encouragement from the parents,” she explained. “They typically leave the nest on their own, when they’re ready.”

Among songbirds, all the young from one nest typically fledge within 24 hours of each other. This sudden departure unfolds every year with the phoebes nesting on the side of my house. One afternoon the nest is overflowing with baby birds and the next it is empty and still.According to Bailey, songbirds incubate their eggs once they are all laid, resulting in the eggs hatching, more or less, all at once. This is not the case with birds of prey, which incubate their eggs as they are laid, so that hatching and fledging occur in staggered increments.

While most nestlings need no encouragement to fledge, cavity-nesting ducks, such as hooded mergansers and wood ducks, are exceptions to the rule. Just 24 hours after her eggs hatch, a mother wood duck will leave the nest – often a hole high up in a tree – check for predators, and then call to her young to leap down. She doesn’t help them, explained Bailey, but she lets them know it’s time to leave.

Despite the perils of fledging, it is in a bird’s best interest to do so as soon as possible, first and foremost because predators may find the nest. The other reason is better access to food. “Being a helpless nestling means you have to wait for food deliveries,” Bailey said.

But that doesn’t mean they are left to fend for themselves. Most birds will continue to feed their young for days, weeks, or even months after fledging. For birds of prey, the maturation process takes much longer than it does for songbirds, according to Sara Eisenhauer, Director of the Center for Wild Bird Rehabilitation at the Vermont Institute of Natural Science (VINS). “It takes months for raptors to fully develop and become independent,” Eisenhauer said. During that time the young will return to the area of the nest for regular feedings.

But even with their parents’ help, fledglings are extremely vulnerable. Which brings me back to the baby ruffed grouse. Had I done the right thing when I did nothing at all? I had, according to Eisenhauer. Between mid-May and late September, VINS receives hundreds of calls from people fretting about a baby bird they have found on the ground. “We strongly encourage folks not to disturb the fledgling bird, for constant interference will discourage the parents from coming to it,” said Eisenhauer.” Best to watch from a distance and let the parent do its job.

The day after my brief encounter with the young grouse, I was walking very near where I had spotted it. As I crested a low knoll, several baby ruffed grouse skittered into the woods. Their mother appeared, flapped her wings, squawked, and frantically paced. I hurried away to ease her distress, and as I looked back, she slipped into the thicket, following her chicks.

Carolyn Lorié lives with her rescue dog and very large cat in Thetford, Vermont. The illustration for this column was drawn by Adelaide Tyrol. The Outside Story is assigned and edited by Northern Woodlands magazine and sponsored by the Wellborn Ecology Fund of New Hampshire Charitable Foundation:

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The Adirondack Almanack publishes occasional guest essays from Adirondack residents, visitors, and those with an interest in the Adirondack Park. Submissions should be directed to Almanack editor Melissa Hart at

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