Since earliest times, people have wondered about the comings and goings of birds. Ancient Greeks explained their seasonal disappearance by a belief that they buried themselves under mud for the winter. People in the Middle Ages thought birds wintered on the moon. It wasn’t until world travel became more prevalent that people began to comprehend patterns of bird migration, and even in the twenty-first century, scientists are still unearthing new mysteries about it. If they still have questions, is it any wonder that the rest of us do?
Q Why do birds migrate?
A Most birds that breed in the huge landmasses of the Northern Hemisphere feed on insects, fruits, fish, and weed seeds — foods that disappear or are covered with ice or snow in winter. These birds must migrate south to find suitable food in winter, but they return north apparently to capitalize on the rich food and fewer competitors during the breeding season.
Although many people assume that birds migrate to escape cold winter temperatures, birds can actually survive very cold temperatures, as long as they have enough food. Even tiny birds, such as Boreal Chickadees, can survive temperatures as low as –50°F (–46°C). They survive the long winter months by eating spruce seeds and insects they have stored in the crevices of trees.
Q How far do birds migrate?
A It depends on the species. Some birds don’t migrate at all, such as Florida Scrub-Jays, which remain near their area of birth for their entire lives. A few mountain species such as Sooty Grouse just move up and down the mountain with the seasons. Depending on where they live, individuals of some species, such as American Robins and Dark-eyed Juncos, may move less than a hundred miles.
Other species travel thousands of miles each year. Eastern Kingbirds that nest as far north as Canada’s Yukon, Northwest Territories, Labrador, and Newfoundland migrate all the way to South America for the winter. Arctic Terns and many shorebirds that nest on Hudson Bay or the Arctic tundra winter in southernmost South America, traveling 24,000 miles (38,625 km) each year between their nesting and wintering grounds. Arctic Terns may travel as far as 1,800 miles (2,897 km) between resting and feeding stops during migration. Some Pacific Golden-Plovers migrate between western Alaska and the Hawaiian Islands, an overwater journey of more than 3,000 miles (4,827 km). Sooty Shearwaters have the longest migration on record: they travel about 40,000 miles (64,360 km) each year, traversing the Pacific Ocean in figure eights.
Q How do birds know when to migrate?
A From the time they hatch, migratory birds apparently respond instinctively, growing restless as the day length and angle in the sun change in spring and fall. Ornithologists have termed this migratory restlessness Zugunruhe. Even individual migratory birds that have been hatched and reared in captivity experience this urge.
By responding to day length, birds arrive on their breeding grounds at the best average time, regardless of weather conditions wherever the bird has wintered. In fall, this restlessness helps ensure that the journey will take place while rich food resources are most likely available, or, in the case of birds that must cross large bodies of water without stopping, that they consume rich food supplies before starting out. Many people assume that their feeders will entice birds to remain too long, but Zugunruhe ensures they do not.
Although this migratory restlessness provides the urge to move, conditions from day to day may provide the impetus to send birds packing. In spring, Neotropical migrants usually wait for northerly storms to pass over rather than flying into headwinds. Birds wintering in the southern United States often begin moving north with good weather. Robins and geese seem to follow the 37-degree isotherm (the “line” visible on a weather map where temperatures average 37°F [3°C]), from which they can backtrack when a sudden deep freeze puts them in danger.
Spring arrival dates for these species can vary widely from year to year. Birds wintering in the tropics can’t predict what weather will be like in the north, so their flights are more precisely tied to day length. One concern for them with continued warming trends is that insect emergences are now beginning earlier, coinciding with warm weather. Meanwhile, the Neotropical migrants arrive and begin nesting and raise their young at closer to the normal arrival dates, and now seem to have a poorer chance of capitalizing on the greatest insect abundance while raising their hungry young.
Goldfinches move south in winter following a pattern that seems to coincide with regions where the minimum January temperature is no colder than 0°F on average.
A BIRD’S GOTTA FLY WHEN A BIRD’S GOTTA FLY
Researchers study migratory urges by putting birds in an orientation cage, called an Emlen cage after the scientist who designed it. It is a funnel shape in which birds can stand upright. Birds that are in a migratory state try to escape from the cage by moving from the bottom area up the sloping walls. Early models had an ink pad on the bottom, and birds would leave footprints on the funnel walls as they tried to fly up. Newer versions may be lined with typewriter correction paper or another material so that the birds leave scratches as they move about.
These marks are distributed fairly randomly by non-migratory birds or birds not in a migratory state, but show strong directionality in migratory birds undergoing Zugunruhe. Some modern cages also have perches fitted with microswitches that register a signal whenever a bird alights. These cages indicate how birds undergoing Zugunruhe are much more active than others, and also show preferred directions and length of time spent traveling.
Q How do migrating birds know where to go and how to get there?
A Some species, such as cranes and geese, learn their migratory routes from their parents. They follow their parents on their first flight south, and sometimes for part of the return trip north in spring, and then are on their own. Most birds, however, cannot depend on their parents to lead the way. Young hummingbirds and loons migrate days or weeks after their parents have left, and yet the young birds know which way to head, how far to go, and when to stop. The more we study the intricacies of orientation and navigation, the more miraculous it seems.
In some cases, birds head in one direction for a certain distance and then change course. For example, Blackpoll Warblers start their migration in an easterly or southeasterly direction from Alaska and northern Canada toward the Atlantic coast. They bulk up, often doubling their weight, and then strike out over water on a journey that can take from 36 to 88 hours without a single break for food or rest, traveling 1,500 to 2,200 miles (2,414 to 3,540 km) nonstop until they reach South America. They start out over the ocean heading southeast, aided by northwesterly winds. As they approach the Tropic of Cancer, they start encountering the northeast trade winds, which deflect their flight to the south or southwest and provide favorable tail-winds as they make the final push toward South America.
In this case, favorable tailwinds may help send the birds in the right direction, but they can use other navigational aids as well. Research scientists are teasing out the environmental cues long-distance migrants use, including the earth’s magnetic fields, the movement of stars in the sky, and polarized light patterns. Recent research has discovered a neural connection between the eye and a part of the forebrain that is active during migrational orientation. This suggests that the visual system is involved in the birds’ ability to sense the earth’s magnetic field. Some species may also use visual landmarks, such as mountains or rivers below them.
ADOPTIVE PARENTING
Beginning in 2001, a population of captive-reared Whooping Cranes have been learning their migratory route by following an Ultralight aircraft driven by crane-costumed handlers that the birds are imprinted on. The birds follow the tiny plane from Wisconsin to Florida their first autumn, then make the return trip and subsequent journeys entirely on their own. Eight years after the first release, some of the birds are starting to breed, and ornithologists hope that soon this introduction will be providing a self-sustaining population of this endangered species.
Q How do birds prepare for long migrations?
A As days shorten at summer’s end, photoreceptors in their brains trigger hormonal changes that stimulate many birds to molt into new feathers that will stand up to the rigors of a long flight. Their hormones also trigger a huge appetite, and they start eating voraciously, gaining significant amounts of weight. Many insectivorous species supplement their diet with fruits, grains, and other items that can be converted to body fat, which birds burn efficiently for energy. These hormonal shifts make birds increasingly restless, especially at nighttime. Suddenly, one day it’s time to go!
Many of the best places for witnessing migration are along coastlines and bluffs. Watch for hawks and other birds that ride on thermal air currents. Warblers, thrushes, and other songbirds that cover long distances by night are more likely to be down in the vegetation feeding and resting. You can often find them by listening for chickadees, because when warblers and vireos are passing through an unfamiliar area anywhere in North America, chickadees allow them to join their feeding flocks. Chickadees know where the best food is and where predators are mostly likely to be lurking.
Q I’ve noticed that the male Indigo Buntings in our area look so bright and shiny in the spring, but by the end of the summer, they are drab and dull. What happens to them?
A Late every summer, after breeding, male Indigo Buntings molt out of their bright blue feathers into drab brown ones. They keep these feathers through their migration to the tropics and during most of the winter, and then in late February or early March they molt into their bright blue feathers once again just before returning north.
Bird feathers are wonderful for protecting their bodies from extreme temperatures, rain, wind, and too much ultraviolet light, but over time feathers grow frayed and parts break off. Molting provides a great way of replacing them before their general wear and tear cause problems. In the case of Indigo Buntings, the bright blue plumage of males is very useful when they’re trying to attract mates and defend their territories but is not so helpful in winter, so the feathers they grow at that time make them less conspicuous.
By the way, the blue in their feathers is due to the way the outer layers of cells in the feathers reflect light, not due to any pigments. If you were to grind up a few male Indigo Bunting feathers, you wouldn’t see a trace of blue — the feathers are pigmented to be dull grayish brown. The blue color is most intense when sunlight is bouncing off it, and least intense when the bird is backlit or in low light.
I’ve often been asked if hummingbirds hitch rides on the backs of geese while migrating — a rather charming concept but definitely a myth. So where did this idea come from? Once I saw a Ruby-throated Hummingbird that was perched on a wire become suddenly agitated. I looked up in the direction it was looking to see a Bald Eagle flying high above. The eagle had apparently crossed into the hummingbird’s column of defended airspace, and the hummer took off straight for it.
When it reached the eagle, the hummer started dive-bombing it on the upper back and nape, up, down, up, down, like a little avian yo-yo. Eventually, the eagle must have crossed out of the hummer’s defended airspace. At that point, the little guy flew back down to his wire, chirping animatedly like he’d chased the big bruiser away.
Hummingbirds will attack virtually any large creature that enters its feeding territory. I wonder if someone once saw a hummingbird dropping down or flying toward a goose and thought it was hitching a ride, rather than maneuvering for an attack. I did read of one account by a hunter who shot a goose that had a dead hummingbird tangled in weeds on its back. If true, that’s hard to explain, but it may be because the hummer got tangled while doing a dive-bomb. I think people just find it hard to believe that tiny hummingbirds can migrate so far — it may just seem more believable that they hitch a ride!
In fact, though, hummers can even fly across the 600-mile (965 km) Gulf of Mexico on their own. We know this because specially licensed bird banders capture, weigh, and band hummingbirds in southern Texas, Louisiana, and Mississippi before they cross the Gulf. Other researchers capture the hummingbirds when they arrive on the Yucatán Peninsula and weigh them again. The average difference in weights fully accounts for the birds flying nonstop over the Gulf of Mexico on their own power.
Q Why do I see some species every winter, but other species only every few years?
A Some food and nesting resources are predictable and found readily year after year, but some vary greatly. Robins can return to the same yards every spring for nesting, and except in extreme droughts can count on a fairly regular supply of worms for feeding on and mud for nest building. But in winter, the trees of one area can be rich in fruits one year and barren the next. So they wander widely in winter. Many finches depend on conifer seeds during the winter. One year conifer cones may be abundant in one area, and the next year birds may have to travel hundreds of miles to find the same food. The birds that move about feeding on these unpredictable food sources are called “irruptive.”
Q Why do some hawks migrate and some stay through the winter?
A Different hawks specialize on different prey. Those that eat rodents in large fields can either head for South America and find rodents in large, summery fields down there, as Swainson’s Hawks do, or stick it out in the north, as Red-tailed Hawks do, grabbing animals in large fields whether they’re peeking out from the snow or running across a road.
Peregrine Falcons that specialize on shorebirds often fly all the way to South America; those that learn to catch city pigeons can spend the entire winter in the north. Some individual Cooper’s Hawks have learned to exploit bird feeders for easy prey. They remain north while other individual Cooper’s Hawks head to Central America to feed on warblers, tanagers, and orioles.
Q Every summer most of my hummingbirds disappear for a few weeks and then suddenly reappear in large numbers. What’s going on?
A Adult male hummingbirds aggressively defend their territories, and if your yard is within the territory of one, he may drive all other male hummingbirds away during the nesting season. If you have a nesting female nearby, she will visit your feeder only periodically, spending most of her time incubating her eggs.
After the eggs hatch, she usually concentrates her feeding at flowers that supply tiny insects as well as nectar. Insects contain the protein that her nestlings need in order to grow, and she’s regurgitating a slurry of the nectar and insects she’s eaten to feed them. Once the young have fledged, she continues feeding them for several days until the fledglings have mastered getting their own food.
At this time, she may bring them to your feeders to teach them how to take advantage of this easy food supply, too. This is also when males stop defending a territory and begin migrating, with adult females soon following. Many of the hummingbirds that suddenly appear are actually migrants from farther north, just passing through.
Q I’ve heard that many songbirds migrate at night. Why?
A There are several major advantages to nocturnal travel.
Temperatures are cooler and the air is moister, protecting them from overheating or dehydrating.
Winds are often lighter, helping them to conserve energy.
Songbird-hunting hawks are active by day and nocturnal owls don’t chase prey in midair, so migrants are safer from predation at night.
Since songbirds require daylight to see and capture their food, nighttime travel allows them to spend their days fueling up for the next leg of their journey.
Q How do birds see where they’re going when they migrate at night?
A They navigate by sensing magnetic fields and by using the stars to orient themselves in the right direction. Birds, like us, have “rod” cells in their retinas, providing some limited nocturnal vision. And, also like us, they have an easy time seeing the stars. But they can’t see other objects in the sky or below them very well, particularly on moonless and cloudy nights.
Researchers have long suspected that some migratory birds can use the earth’s magnetic field to orient. One classic study in the 1960s involved homing pigeons wearing tiny metal helmets. Half the helmets were magnetic; the other half were the same weight and size but not magnetic. On sunny days, all the birds found their way home easily. On cloudy days, the birds sporting magnetic helmets didn’t orient or find their way back, at least not until the sun came out again.
More recently, researchers have discovered deposits of magnetite in the nasal tissues of several migratory species, including Bobolinks and White-throated Sparrows, and have learned that some neurons in visual centers of the brain respond to changes in the magnetic field. In darkness or red light, these birds may become disoriented, but in white, green, or blue light their sense of direction is normal.
In 2004, a European team studying the Garden Warbler discovered light-sensitive pigments in the retina that influence how the bird’s sensory cells react to the magnetic field. It’s possible that the curvature of the retina and the position of the magnetite in the nares (nostrils) may create some sort of pattern as they respond to the magnetic fields, perhaps producing a visual color shift when facing north or south but not east or west. This would explain why birds grow disoriented in some colors but not others, but we don’t know if the birds’ perception of magnetism is through vision or some other sense that we mere humans can’t even imagine.
Q How do scientists know that birds use the stars for navigation?
A Fascinating research projects conducted in planetariums were begun in the 1950s, when European scientists Franz and Eleanor Sauer discovered that Garden Warblers fluttered away from the projected North Star, even when the projection was rotated to place the North Star in another direction. During the 1960s, American scientist Stephen Emlen showed that birds don’t recognize one particular star but actually the pattern of stars revolving around the one fixed star. He raised young Indigo Buntings in a planetarium, under a projected sky with stars revolving around Betelgeuse. During the birds’ first autumn, they oriented to fly away from Betelgeuse.
Apparently young birds spend part of the nighttime awake, gazing at the night sky. They seem to notice that the stars move in a circular pattern, and instinctively know that the one fixed star that never moves is “north,” and they can find it by learning the pattern of the stars around it so they can figure out where north is even when the sky is covered with patchy clouds.
Millions of migrating birds strike high-rise buildings every year. What can we do? Toronto’s Fatal Light Awareness Program (FLAP.org) patrols downtown Toronto in early morning to rescue live birds and collect dead ones. They urge people to turn off lights or close drapes during migration. Chicago, Minneapolis, and San Francisco have similar programs.
Q Do birds migrate directly north and south? How do they compensate for crosswinds?
A Few birds fly directly north or south. Many species, such as Blackpoll Warblers, have adaptations allowing them to capitalize on specific feeding or flying opportunities along their route. Many of these birds start out heading east-southeast toward the Atlantic Coast, and then take off over the ocean toward South America, aided by trade winds. To aid their long flight, their primary wing feathers are longer than those of warblers, such as Pine Warblers, that make shorter flights.
Ruby-throated Hummingbirds fly generally south until they reach the Gulf Coast, and then take advantage of abundant food in the Mississippi Delta to build up their fat reserves. Then many of them take off over the Gulf, flying nonstop to the Yucatán. But there is evidence in both cases that some individuals hug the coastline rather than making such a long overwater flight.
The flight direction of migratory birds in general depends on where their final destination is, whether the stars are visible, and a lot of individual factors. For example, thrushes have a very strong sense of direction. From a given departure spot, though, each bird takes a different heading. They’re all moving in general toward their species’ winter range, but a winter range can be large — it wouldn’t be very good for all the birds to end up in exactly the same spot!
Q Since they can fly away, why do some birds stay in extremely cold places for the winter?
A The average annual adult survival rate of year-round tropical residents is 80 to 90 percent. The average annual adult survival rate of migrants is about 50 percent. And the average annual adult survival rate of temperate zone year-round residents is only 20 to 50 percent, because of the difficulties of surviving severe winters. Why don’t these northern residents head south to improve their odds?
The evolutionary game is won not by the birds with the longest lives but by those who produce enough young to replace themselves. Year-round residents can select the best territories long before migrants arrive and can work out territorial differences well in advance of the breeding season so they aren’t depleted by the rigors of both a long journey and territorial battles right when they start nesting. They can also get an earlier jump on nesting, allowing them more time to re-nest if their first attempt fails.
Q Migrating seems so dangerous and the birds must use so much energy to fly such great distances. Why do they do it?
A Migration in birds probably evolved many times, for many reasons. The northern temperate and boreal zones are vast and rich with insects; they have fewer marauding insects such as army ants, and fewer poisonous snakes and spiders than are found in the tropics. The northern latitudes also have significantly longer summer days than tropical zones, providing more hours for feeding young each day and significantly reducing the amount of time vulnerable young remain in the nest.
BLOWN OFF COURSE
Although the mechanisms of bird orientation and navigation are amazingly intricate, some storm systems are powerful enough to send migrating birds far off course. Individual North American songbirds, including several species of warblers, Dark-eyed Juncos, White-throated Sparrows, Scarlet Tanagers, and Rose-breasted Grosbeaks, have been carried all the way across the Atlantic, especially to England and Ireland, frequently enough to be included in some field guides to the birds of Europe. A few Siberian birds appear with some regularity in North America, especially Wheatears and Bramblings. And some birds seem to have a compass that can become so disrupted it entirely reverses their migration, such as Fork-tailed Flycatchers from South America that have turned up dozens of times in North America. To see the migration routes of warblers and other birds, go to http://bna.birds.cornell.edu/bna/species/431/articles/migration.
Some birds breeding in even northernmost North America may well have originated as tropical residents who, to escape competition and take advantage of huge insect population explosions in the north, started heading to the vast northern landscape to breed, retreating “home” to the tropics again after the breeding season. A full 78 percent of all northern migrant species, including flycatchers, swallows, vireos, wrens, and orioles, have close relatives in the same genus or even the same species that are year-round Neotropic residents.
Some non-migratory populations have probably become migratory as conditions changed for them. One example that we’ve been able to observe firsthand: non-migratory House Finches from the Southwest were released in New York in the early 1940s. Within 20 years, some of these birds had begun migrating to the Gulf States for the winter and returning north to breed. Other individuals remain year-round in the Northeast. In just two decades this species has become a partial migrant.
Q I’ve heard you can tell if birds are migrating on a particular day by looking at a weather map! How does that work?
A It’s true. Weather radar images show where radar beams have been “reflected” as they sweep the atmosphere. They’re useful for showing weather conditions because the beams are reflected by precipitation and the water vapor in clouds, but they can also be reflected by swarming masses of birds or insects.
In the early days of World War II, British radar operators noticed mysterious, ethereal shadows drifting across their screens. They weren’t associated with weather systems and so the radar technicians nicknamed them “angels.” In 1958, a New Orleans high school student named Sidney Gauthreaux, realizing that these “angels” were really the radar reflections of swarms of birds, started scrutinizing radar images. As a Louisiana State graduate student, he worked with radar images to document the existence of massive trans-Gulf migrations.
In the late 1980s, Gauthreaux started examining archival radar images and made a disturbing discovery: major bird movements over the Gulf had declined by nearly half since the 1960s.
Next Generation Radar (NEXRAD) made studying bird migration much easier. The Air Force started using it to avoid collisions in their Bird Aircraft Strike Hazard program. Graduate students took stunning images of giant expanding aerial doughnuts, which they found to be thousands of Purple Martins radiating from critical roosting sites each morning.
Now it’s easy for anyone with access to a NEXRAD weather map on their computer to see birds take off on migratory movements at night or alight in the morning, if you know how to interpret the mystifying patterns. You can learn how at www.virtual.clemson.edu/groups/birdrad/.
Fall migration, when many birds fly over the Gulf of Mexico, takes place during hurricane season. Birds can be killed outright by high winds, hail, blowing debris, falling trees, and so forth. They can be blown too far off course to survive. Birds passing through a devastated area after a storm may have trouble finding feeding resources, or may succumb to pollutants released in hurricane-related oil, gasoline, and other toxic spills caused by flooded automobiles, households, oil refineries, chemical manufacturers, and other sources.
Most migrants don’t encounter hurricanes and avoid damaged areas. But there are plenty of other dangers out there. Communications towers in their flying space may kill as many as 50 million migrating birds per year. Occasionally in foggy or stormy weather when birds are flying over open water in the Gulf or the oceans, they are attracted to the lights of a lighted vessel and dash against the windows, injuring or killing themselves. And if they survive the dangers of the night, come morning, they have to negotiate whatever habitat they find themselves in.
Cities can be treacherous. An estimated 500 million to one billion birds are killed each year in the United States in collisions with windows. Many of these deaths take place at lighted high-rise windows at nighttime, and many take place in the morning against plate glass windows and doors at ground level, when birds find themselves in a heavily urbanized area where the only vegetation is inside hotel lobbies and solariums. Habitat degradation, especially along coasts and shorelines, can make obtaining food difficult for migrants right when they need it most. As a wildlife rehabilitator, I cared for several loons, grebes, and rails (shy little marsh birds) that had crashed onto sparkling wet pavement where a wetland existed the previous year.
One researcher found that apparent mortality rates of Black-throated Blue Warblers were at least 15 times higher during migration than during the breeding and winter resident periods; more than 85 percent of apparent annual mortality of this species occurred during migration!
You can see a map of where any wintering species were reported in mid-February in the United States and Canada during any winter since 1999 on the Great Backyard Bird Count map; the website is www.birdcount.org.
Q Do birds nest again once they reach their wintering grounds?
A No. Northern birds spend winter eating food in the tropics and, sometimes, molting into new feathers. Raising young takes tremendous amounts of energy, and few migratory species can afford to do that for longer than a fairly brief period of time in their annual cycle.
Canada Geese were introduced into Great Britain as early as the 1600s. Four centuries later, the geese on the British Isles are still non-migratory. Canada Geese were introduced into Sweden during the first half of the 1900s. These geese have become migratory, many headed to Scania, in the southernmost tip of the Scandinavian Peninsula, and to the East German Baltic coast.
Q What do birds do while they are “on vacation” in the tropics? Do they just loaf around and eat?
A Many birds, males and females alike, use as much energy defending a winter territory as they do a breeding territory. There are great advantages to knowing every inch of a familiar plot of land for finding food, hiding from predators, and having safe roosting places. There are many dangers in the tropics, and birds must compete with a tremendous number of other birds for resources.
Some birds, such as Eastern Kingbirds, that specialize on a high-protein insect diet in the north while producing eggs and feeding young may switch to a fruit diet in winter. Fruit-eaters such as these may be highly territorial in summer, but on their wintering grounds peaceably associate in flocks, wandering widely in search of new food supplies.
Whether they defend a winter territory or associate in a flock, wintering birds must recover from their arduous autumn migration and get back in condition to migrate north all over again when the time comes.
Q Do any Central or South American birds spend their winter up here in North America?
A A few individual southern birds wander north after their own breeding season, but those are anomalous cases. About 220 to 240 austral migrants (birds that breed in the Southern Hemisphere and migrate north for their winter) breed in temperate South America and winter toward the Amazon basin. Most austral migrants do not winter as far as the tropics — only 32 species reach Amazonia and 14 more winter north of the Amazon basin. This, by the way, compares with about 420 species that breed in temperate North America and winter in the Neotropics.
Q Robins are supposed to be harbingers of spring but I see them all winter in Minnesota! How is that possible?
A Robins switch their diets from primarily worms and insects in spring and summer to primarily fruits in fall and winter. They can survive as far north as they can find a consistent supply of food. Robins are interesting migrants — rather than a north–south route, they wander more loosely in search of their winter diet of fruits and berries, which are unpredictably abundant in some places and sparse in others.
Those robins that remain in the far north tend to be males who get the advantage of arriving first and claiming the best territories in spring, if they survive the winter. They will move on if they deplete the food supplies, and some succumb to bad weather and starvation. So the genes for longer distance migration remain alive in the population, too. Major spring migratory movements of robins follow the thaw pattern when earthworms first appear, about where temperatures are starting to average 37°F (3°C). But in many northern areas, wintering robins are around long before the “first robin of spring” arrives.
How do you tell that first robin of spring from the last robin of winter? If they’re feeding in flocks in fruit trees, they’re still exhibiting winter behaviors. When they run on lawns feeding on worms and start singing, they’re showing spring behaviors; usually spring robins are seen as individuals, pairs, or fighting rivals. In the changeable conditions of early spring, a robin may exhibit spring behaviors one day and revert to winter behaviors when a late blizzard blows in.