Once upon a time, in a land far from people, a tiny egg cracked in its nest. Slowly, a small beak pushed through, delicately casting pieces of eggshell aside. It was followed by dark grey bulges that were closed eyes, and finally a floppy, mostly featherless and helpless body that weighed only 3 grams .
This hatchling was nestled warmly among a few siblings in a twig-shaped cup lined with grass and caribou hair in a small depression in the ground . Although she didn’t know it, her nest under a bush was in a vast wilderness in Alaska. What she did know was that she was hungry. What began as a feeble and silent head raise to open her mouth and beg for food, later became relentless begging accompanied by tiny peeping sounds. Both of her parents stuffed her and her siblings full of insects such as butterflies and stoneflies . Summer days and nights passed with hardly any darkness and so much birdsong. Nearby she could hear the melancholy sound from her parents singing “Oh, dear me” in a dialecta that was unique to the region in which she was born .
Eventually, when she was about 10 days old, her eyes were alert, and her body was covered in warm feathers. She was stronger and ready to fledge—to join her parents in the sea of bushes outside her nest. However, she was not yet able to fly and could only walk. She hesitated to leave at first, but then a Northern Shrike (Lanius excubitor) attacked her nest. She hopped away just in time, but one of her siblings left the nest in the shrike’s mouth .
When she first flew above her nest days later, she saw similar bushes that seemed to stretch all the way to the tall snow-capped mountains lining the horizon. She noticed there were other birds like her nearby, some with just a subtle yellow crown who were leaving their nests for the first time, and others with striking yellow and black crowns singing songs to communicate which areas they had claimed as territories . She could see a vivid world filled with ultraviolet colors and magnetic fieldsb . While her parents had begun to moltc their feathers, she practiced the song of her home.
As the days became shorter, each morning there seemed to be fewer birds singing. The little bird suddenly got the urge to eat—a lot! As she ate, she felt herself become heavier. She was putting on fat, but at the same time her muscles and heart were growing larger . Eventually she had so much fat that it seemed to bulge out from the area under her throat, her furculum.d Then, one night, instead of sleeping, she was restless. So restless that she needed to fly. She needed to fly, in the dark, higher than she had flown before. So, she flew away from her nest bush, away from her family, away from the sea of bushes and familiar birdsong. Only a few inches long, she flew higher and higher into a night sky shimmering with so many stars—and she didn’t stop.
A few hours later, in the middle of the night, she landed. She was in a new place and it was dark, but she knew she was heading in the right direction. She needed to find a safe place to rest before the sun rose and she could eat again. The next night that restlessness—that Zugunruhe—came again.e Night after night, for about a month, she traveled. Sometimes she rested in the same place for a few days before moving on. Sometimes she only stayed one day. She noticed that the further she flew, gliding away from the wilderness, the more often the ground far beneath her grew brighter, looking like stars on the ground instead of just in the sky.
One morning as she was eating to replenish the fat and protein she had burned to fuel the trip , she looked up to see the talons of a Cooper’s Hawk speeding toward her. With her quick reflexes she bolted away just in time into some nearby bushes, heart pounding.
After so many days of traveling, for reasons only she knew, the little golden-crowned sparrow finally stopped. Her Zugunruhe was replaced with a different feeling. The next morning she saw that other birds like her were gathering in flocks instead of staying in separate territories, and she joined in. She was careful to give the more dominant birds their space, otherwise they might hop aggressively toward her . Together, the group searched for food and watched for predators. Some of the other birds had black and white instead of yellow on their heads.
One afternoon, two humans walked by. She had become accustomed to seeing them now that she was in California. One said, “I don’t know what those are—just a bunch of little brown birds I guess.”
“No,” said the other. “The ones with yellow are Golden-crowned Sparrows, and the ones with white are White-crowned Sparrows.”
“Oh, well, sparrows are boring. Let’s go look for some bluebirds or hawks or something.”
Then the humans left.
The winter passed with rain and sun, and some cold. She learned where to find seeds, fresh sprouts, and grain to eat. She learned the alarm calls from other birds that indicated when a predator—often a house cat—was nearby . She even molted her crown feathers and now had more brilliant colors on her head. She had grown into an adult. Months later, when the days were getting longer, she was hungry once again. The feeling was familiar, and after fattening up and experiencing that restlessness, she left again in the night.
Speeding away from the cities of California, she could see the stars again as the lights faded into the distance. After a few weeks, somehow, she knew she was home. She was early enough that male birds were just determining their territories; if she had been late, she may have missed getting a good territory or missed the feast of insects soon to cloud the air as the warmth of spring arrivedf .
Back in Alaska, she heard familiar song dialects and a male sang to her while carrying a small tuft of grass . The days were long again, and the vast wilderness was still there. Yet, she was different. Soon, she would be laying eggs. Soon, she would be relentlessly feeding a new generation of helpless hatchlings in her nest. And then, she would do it all over again.
Autumn Iverson is a PhD candidate in the Graduate Group in Ecology at UC Davis. Her research interests include songbird migration and the impacts of environmental change.
a While most birds have a song that is typical of their species, some birds (including Golden-crowned Sparrows) also have different variations of their song—called dialects—depending on the geographic area where they grew up. One species may have many different song dialects, and the dialects can impact birds’ social behavior. For example, individuals of some species will only mate with others that share their dialect .
b Birds can perceive ultraviolet light (i.e., short-wavelength light that is outside of the range of colors that humans can see). This type of vision may help them signal to mates or locate food, since many fruits, seeds, and insects reflect UV light . It is also thought that some migratory birds have the ability to sense the Earth’s magnetic field, providing a sort of internal compass that may help them navigate during long-distance migration.
c Molting is when birds shed their feathers and grow new ones; this generally occurs once or twice per year in songbirds like Golden-crowned Sparrows. Molting is an important process for maintaining healthy feathers and flight ability.
d Before leaving on migration, sparrows may increase their body weight by 15% or more, much of which is stored as fat in their furculum (a special structure on the bird’s upper chest). This stored energy helps sustain the birds over long stretches of non-stop flight during migration.
e The German term Zugunruhe describes the restless behavior of migratory animals like birds around migration. This restlessness serves as an internal cue telling the animal it’s time to depart.
f Many birds arrive at breeding grounds and time their reproduction so that egg laying and chick rearing correspond with the period when food sources, like insects, are most abundant. Poor timing in relation to food abundance means a bird might not have as much food to feed its growing chicks, putting them at a disadvantage.
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Edited by Jessica Schaefer