Q. When do robins leave their wintering grounds?
A. Robins
typically start moving northward from Florida and the Gulf states, and
tend to follow the 37-degree average daily isotherm. Migratory restlessness builds up as day length increases. Scientists call this "zugunruhe," a German compound word consisting of Zug (move, migration) and Unruhe (anxiety, restlessness).
Q. Why do robins migrate?
A. Robins migrate because the ground freezes, locking them out from their favorite food, earthworms, and because winter weather makes it impossible to find juicy caterpillars and other insect food. Robins switch their diet to fruit in winter, but there is not enough fruit in the north to feed all the robins that live in the north all summer. That's why most robins move south.
Q. How fast do robins fly during migration?
A. Robins fly about 30 - 36 m.p.h. during migration.
Q.
How far do robins usually fly each day when they migrate north?
A. Robins can fly for many hours each day, so on days with good migrating
conditions, they probably cover roughly 100-200 miles per day.
Q.
Do robins migrate along the 37-degree isotherm?
A. Yes, the
huge bulk of male robins follow this migration pattern in spring, though
there is a wide amount of variation among individuals.
Q. How do weather patterns influence robin migration?
A. Robins
often move ahead of warm fronts, arriving just before or along with rainy
weather. This means they arrive right when earthworms must emerge from
their tunnels or drown.
Q.
How far is the robins' migration?
A. Some robins
fly thousands of miles, such as the individuals that migrate from Vancouver
Island to as far south as Guatemala. Others don't migrate at all, such
as robins that breed in southern Mexico and Baja California. Most robins
migrate intermediate distances.
Q.
Do robins migrate by day or night?
A. Although
robins occasionally migrate at night, they mostly migrate during daytime.
Q. How do robins find their way when storms blow them far off course?
A. Robins figure out their location on the planet in much the way sailors
on the high seas once did--using the angle of the sun in relation to the
time of day. If blown off course, they fly to where the sun will be at
the proper angle.
Q. Do all the robins survive the migration?
A. No! Scientists
estimate that only 25% of fledging robins survive until November. And
many experienced adults die during migration, too.
Q. Which returns first: males or females?
A. Male robins
arrive on the breeding grounds a few days to two weeks before the females
return. You can tell male robins because their head and tail feathers
are very dark black and bright orange in comparison to those of the female.
When the first females arrive later, you'll notice their plummage appears
faded and drab in comparison to that of the males.
Q. What
do robins eat when getting ready for their migration?
A. At winter's end, robins eat a lot of berries. They also eat as many worms
as they can find at the start of spring migration. In late summer and
early fall they prepare for migration by eating a lot of fruit and insects
as well as worms.
Q. Do robins travel together when they migrate?
A. Yes, they form loose flocks for both feeding and flying during migration.
Q. What are the best weather conditions for robin migration?
A. In many areas, high pressure systems with northwesterly winds are best
for migrating during fall. In spring, robins follow warm fronts.Cool conditions
are better than warm.
Q. What are the least favorable weather conditions for migrating robins?
A. Hot weather gets them overheated. Rain and snow are hard to migrate in.
Ice rain and hail are much worse.
Q. Why don't robins stay in the south? Why migrate north in spring?
A. Robins are very often stressed by heat, and areas where robins winter often have hot summers. Soils in the South can even get so warm and dry that worms retreat deeper into their burrows during hot, dry spells, making them harder for robins to find. Also, a careful look at a map of North America shows a vast landmass with frigid winters but pleasant summers, where earthworms and other robin food thrive. Robins evolved to take advantage of that huge food resource.
Q. Why do females arrive later than males?
A. Male and female robins both feed their babies. But before the eggs hatch, the male and female have different jobs. The female builds the nest, and produces and incubates the eggs. The male chooses and defends their territory, and finds some nest materials for the female to use. He must return early to have a good choice of territories and to protect his choice against robins migrating through. If snow or ice storms limit his food supplies for a few days, he can still easily survive until the next thaw. The female, has no urgent need to return early, since there is nothing important for her to do until there is a good mud supply for building her nest. As a matter of fact, if she builds too early, hard frosts at night can weaken her nest. And if she runs out of food so soon before the nesting season, it can make it hard for her body to produce eggs. So she waits until conditions are more favorable so she can continue to get a reliable winter diet as long as necessary.
Q. Can you tell a migrant just by its size or color?
A. Although different populations of robins are slightly different sizes and the color intensity of the plumage varies somewhat geographically, robins don't really show the cut-and-dried plumage variations that populations and subspecies of others birds do. On average, robins are smallest in the warm, humid southeastern US, and smaller than average along the humid coast of northern California and the Pacific Northwest. Robins are largest in the high, dry Rocky Mountains, northern Great Plains, and northern deserts of the West.
Robin plumage is darkest in birds in the Pacific Northwest and in Newfoundland—both places where the humidity is exceptionally high. The amount of white in the tail is largest in the East and smallest in the West. An isolated robin population in the Baja California Sur is exceptionally pale.
But robins live up to their scientific name, Turdus migratorius (the "migratig thrush"), wandering widely and unpredictably in winter and often ending up in spring in entirely different areas from where they were raised, so there's a lot of mixing. That means that size and color differences among populations are subtle at best; even with perfect views, we can never be absolutely certain where robins came from by either size or plumage.
Q. How do flocks get started in the first place?
A. When a brood of baby robins fledge, they are taken care of by both parents for a few days. Then the female gets ready to lay more eggs. When she starts incubating the next clutch of egge, the male continues to take care of the first brood. At nighttime, he leads them to a nice, well-sheltered stand of trees or shrubs to sleep. Other male robins are also leading their babies to this area, which is called a roost. The young birds get used to sleeping in a big group (flock). When the new eggs hatch, the father leaves his older babies to help feed and care for the new nestlings. The older babies are fine on their own, hanging out with other fledglings. They learn that being in groups, or flocks, is normal. Robins ARE territorial on their summer breeding territories, but not at their roosts, nor in feeding trees. Flocking is a behavior that serves robins well when it's not breeding season. Advantages to being in flocks are that more eyes can search for food sources, and more eyes and ears can be watchful for predators.
Q. How do flocks of mixed species get going?
A. Mockingbirds, waxwings, Pine Grosbeaks, and other fruit-eating birds that join up with robin flocks usually get going when the birds are searching for fruit trees. Hearing fruit-eating birds attracts other fruit-eaters, of the same as well as different species, because they all need the same food.
Q. How do robins prepare for winter?
A. In October they start seriously adding down feathers to improve their insulation for winter. Also, summer food supplies have diminished; there are still plenty of berries around to eat, but robins get seriously on the move in search of plentiful food supplies for the coming winter. They start seriously moving in October. Back on October 1, 1988, birdwatchers counted over 60,000 robins migrating over Duluth in northern Minnesota, so that's serious migration. But in fall and winter, robins don't stay in a single spot for long — they wander about searching for new sources of still-fresh fruits.
Q. How do scientists learn where robins from one state/province migrate for the winter?
A. Scientists study bird banding data to learn where robins go. They put thousands of numbered bands on robin legs, but they know they will only recover data from a few of these birds in the future. So it takes a long time to amass enough data for them to draw accurate conclusions. Meanwhile, robins can change some of their migration patterns, making the research even more complicated. To see the U.S. Fish and Wildlife Service's robin banding data to learn where robins from your area go in the winter, see our Bird Banding Data Study.
Q. When a robin migrates, does it travel in small or large groups, or alone?
A. All of the above! Robins often associate in flocks, and sometimes these are huge. I once counted 60,000 robins flying along Lake Superior in just 5 hours! And sometimes robins fly alone. But over the years that I counted migrants along Lake Superior, most of the robins were in flocks of about 10-50 birds. Over the course of a year, robins each lead two entirely different lives. In spring and summer, they're territorial worm-and insect-eaters. In fall and winter, they switch to berries and other fruits and live in sociable flocks. Robins migrate and spend the winter in flocks to make it easier to spot predators.
Q. Do robins migrate by flying close to the ground? Do they rest at night?
A. When robins are flying short distances, between fruit trees and roost trees in a neighborhood, they fly below tree height. When they make major movements, they fly much higher, though lower than hawks and other birds that use thermal air currents. I live in Duluth, MN, on a major robin migration flyway, yet from my own yard, I never see the higher flying flocks. I have to stand on one of the ridges in my area to see the large, high-flying flocks. So I believe it's more an issue of vantage point than anything. They rest overnight in large numbers in trees.
Q. Do robins from different areas in the north travel to different areas in the south?
A. Robins are "nomadic," meaning they wander irregularly. The same individual robin may winter one year in Texas, one year in Florida, and one year in Wisconsin! You just never know.
Q. How long does a robin's migratory flight usually take? Does it depend on different conditions?
A. The spring migratory flight depends entirely on weather, since they follow the 37-degree isotherm. It can take anywhere from a few days to several weeks for a robin to go from Texas to Minnesota, for example. Fall migration never really ends, since robins wander throughout the autumn, winter, and early spring.
Q. Why do robins molt just before they are about to migrate south?
A. They molt so they will have fresh feathers for their flight. These fresh feathers will also be very good for insulating them from the winter cold. Robins start molting their flight feathers in mid-June, and have finished molting them by early September. They molt their body feathers from late July into October. One by one, each feather is pushed out by a new one. Most feathers last for a whole year. If a feather gets pulled out when the robin isn't molting, that feather gets replaced fairly quickly.
Q. Do baby robins migrate alone? How do they know where to go?
A. After a brood of young robins fledge (leave the nest), the mother starts building a new nest and laying new eggs even as she still spends most of the time each day attending to those fledglings. The father spends all day with the fledglings and leads them to a roost at nighttime, where they join with other fathers and fledglings. When the mother finishes laying a new clutch (which takes usually four to six days after her new nest is built), she starts incubating and leaves the fledglings to their father's care. When the new eggs hatch, the father leaves the fledglings on their own and returns to feeding the new nestlings. Those fledglings hang out with the other fledglings from their nighttime roost, finding fruit trees and worms and being sociable, and every night the fathers join them in the roost. As the last broods are done being raised, the mothers join these flocks. So by the summer's end, robin flocks contain birds of all ages that start to wander, looking for new feeding areas that provide some worms and fruit. The young birds hang out with these restless flocks, moving from place to place in search of food, mostly headed in a southerly direction. They don't have to know where to go on their own because of their need to associate with other robins.
Q. How do robins know which way to migrate?
A. There is a powerful instinct that makes them grow very restless in spring and fall. And that instinct includes telling them which way to head. After wandering during winter--and individual robins can go to entirely different places from one winter to the next--robins often find their way to the exact backyard they nested in year after year. As daytime migrants, they may well find their way by using the angle of the sun to guide them. Some birds have tiny bits of magnetite in their brains that helps them know which way is north--I'm not sure if robins have been analyzed for this. The trickiest migration to understand is fall migration. How does a baby robin that has never migrated before know which way to head? Again, more research is needed. But it's quite possible that part of their migration is learned, because young robins tend to join with adults in big migratory flocks. But as with many robin behaviors, it's probably a mixture of instinct and learning both.
Q. Have humans had any effect on how long the robins will stay before migration?
A. Before migrating south, robins often gather in areas with abundant food. The kinds of plants humans grow affect robins because of this. The impulse to migrate is strong in most robins, so even while food is abundant the majority of robins in the north suddenly move on. But when a great amount of food remains, individual robins and groups of robins often remain.
Q. Has there been a change in how early robins are migrating from year to year?
A. During winter, robins are very nomadic. In some exceptional places they may appear year after year, but their wandering may also change dramatically sometimes because of weather and food patterns farther north. For example, if fruit is unusually abundant in Georgia and Tennessee in one fall and winter, the bulk of robins might not bother to migrate as far as Florida. As temperatures grow milder, more robins may winter farther north. But as of now, the biggest February flocks of robins are usually in the St. Petersburg area of Florida, according to the Great Backyard Bird Count.
Q. Is there enough food for wintering robins that do not migrate? How can berries replace worms in regards to nutrition? Don't worms have more protein?
A. You're right that worms have much more protein than berries. But some birds manage to achieve a balanced diet over an annual cycle rather than day by day. Robins require protein especially when females are producing eggs and when both sexes are molting-these activities occur only during the time of year when they're eating worms and insects. During winter when they switch to a diet of fruits, they are getting plenty of vitamins, and the carbohydrates give them plenty of energy to sustain their bodies. Winter is the time when their activity is limited and they aren't growing new plumage or producing young.
Regarding berries, there are many different species, and some have a bitter taste until winter. So some berries are avoided during late summer and fall, and these are the ones that remain for winter food. Robins also eat crab apples. There is clearly not enough fruit to sustain as many robins in winter as live in New Hampshire in summer, but there is enough fruit to maintain a small but robust winter population. And robins aren't like some birds, especially neotropical migrants, that maintain winter territories. When one food source becomes depleted in winter, a robin flock will move to another place. The only time robins are sedentary, remaining in one fixed place for weeks at a time, is duing the nesting season when they are in their territories.
Q. Doesn't a robin know to migrate south? I live in Canada. A robin is wintering in my yard.
A. Robins are a migratory species, but their migration is far more complicated than simply a shift southward. There seems to be a great deal of individual variation in where they spend the winter, though males are far more likely to remain in the north than females. There are good reasons. Come spring, the male's main job is to find and defend a territory. The females' main job is to create and lay the eggs. This requires a lot of good nutrition and food energy, so females go where they are sure of good food supplies in winter. Yes, they have to use up food energy to migrate north. But migrating and laying eggs are easier for well-nourished birds.
Q. Do all robins migrate south?
A.Robins are a migratory species, but their migration is far more complicated than simply a shift southward. There seems to be a great deal of individual variation in how far they go and where they spend winter. Males are far more likely to remain in the north than females. for some very good reasons. Come spring, the male's main job is to find and defend a territory. The females' main job is to create and lay the eggs. This requires a lot of good nutrition and food energy, so females go where they are sure of good food supplies in winter. Yes, they have to use up food energy to migrate north. But migrating and laying eggs are easier for well-nourished birds.
Q. What can I do to help robins in autumn and winter?
A.You can make your backyard bird-friendly. That means don't rake too much. Dead leaves left under trees and shrubs are ideal spots for birds to forage for insects as weather gets colder. You can also provide cover. Birds need shelter from harsh conditions, and vegetation in your yard will help provide it. Don't prune back dead vegetation like vines and stalks, as these provide both valuable winter cover and nesting material for birds in the spring. If you have berry bushes or fruit trees, don't pick them bare because those fruits are food sources for robins migrating through, or overwintering in your area. The best thing you can do is to plant native fruit trees and shrubs that will provide robins with fresh, wild food. To feed them in winter, one Journey North friend set out fruit and mealworms in a heated birdbath filled with sphagnum moss rather than water.
Q.
How do earthworms migrate?
A. In areas where the ground freezes, one sign of spring is the appearance
of the first earthworms of the season. This is called a "vertical migration."
Earthworms, in the fall, migrate deeper into the earth, below the frostline.
Sometimes they ball up to reduce moisture loss--as many as a hundred worms
being bunched together--and thus spend the winter in inactivity. When
spring comes and frost leaves the soil, the earthworms become migrants
again, tunneling upward. They appear at the surface, leaving the first
castings of the new seasons, as soon as the average temperatures of the
ground reaches about 36 degrees.
Q.
How do scientists learn where robins from one state or province migrate
for the winter?
A. Scientists study bird banding data to learn where robins go. They put
thousands of numbered bands on robin legs, but they know they will only
recover data from a few of these birds in the future. So it takes a long
time to amass enough data for them to draw accurate conclusions. Meanwhile,
robins can change some of their migration patterns, making the research
even more complicated.
Q.
How do we tell whether a robin in early spring is a migrant
or a resident?
A. It's usually
impossible to tell by their appearance unless they have been banded or
color-marked, except for one lucky thing. Male robins from Newfoundland
and Labrador are darker than other robins, with almost black backs, brighter
red underparts, more noticeable striping on the white throat, and a bolder
eye-ring. People farther south in Canada and the U.S. may notice the difference
when they spot one of these, and then they'll know for sure that these
are the northern race rather than their own breeding robins. Many magazine
photos of winter robins show these brightly colored ones, which make a
lovely contrast against snow-covered branches and orange berries. But there
is another difference between local and migrant robins. Male robins that
intend to remain in your area will sing their territorial song. Robins
that are passing through will occasionally sing, but not as often, especially
at dawn, and usually they remain fairly quiet.
Q:
How can I predict where my visiting robin was yesterday?
A. Robins
migrate at a speed of about 30 miles per hour, and can migrate during
day or night. They average 38 miles per day, but some days they don't
migrate at all, and other days they can go many times that. So it's impossible
to be exactly sure where your robin was yesterday unless it was wearing
a satellite transmitter.
Q.
What might be some advantages for robins to migrate in groups?
A. While
feeding, the more robins there are, the more likely that at least one
of them will notice a predator and warn the rest. During migratory flights,
hawks have trouble singling out one robin to strike when faced with their
fast-moving, tight migratory flocks. With a large flock, some individuals
may be more familiar with an area than others, and the experienced birds
will show the others the best places for feeding and roosting. Since the
robins are all moving together, no individual will know all the best places,
and most of the flock members will both help and benefit from flock membership.
Q.
Do all the robins leave at the same time?
A. No. Immatures hatched in the first nesting of a season will be ready to
join migratory flocks before their parents or later siblings. Adults who
nest three or more times in a season won't be ready as quickly as those
who nest only twice.
Q.
Where do robins spend the winter?
A. Some robins
retreat all the way to southern Texas and Florida, but others winter as
far north as they can find berries. So robins have an enormous winter
range.
Q.
Many neotropical migrants have a fairly regular migration from year to
year. Why don't robins depart at almost the identical time each spring?
A.Neotropical
migrants have no way of knowing what the weather may be like across the
Gulf of Mexico when they leave their wintering grounds. Most of them migrate
much later than robins, and time their migration by daylength. Robins
are very dependent on availability of worms on their nesting territories.
By following the 37 degree isotherm, they tend to migrate in the kind
of weather systems that bring rain, snow melt, and enough warmth to thaw
the soil so worms will emerge in large numbers. But weather conditions
vary enormously from one year to the next, so robin migration varies,
too.
Q.
How do robins prepare for the journey north?
A. Robins put on some fat when food supplies permit during late winter and
early spring, and again in late summer and early fall, which helps fuel
their flight. Adults molt, growing new body and flight feathers, in summer
after they've finished breeding: these feathers will be fresh for fall
migration, provide maximum warmth in winter, and still be in good enough
condition for spring migration.
Q.
When do the robins arrive in their breeding (summer) home?
A. Male robins
arrive about the time that the average daily temperature is 37 degrees.
Females arrive a few days to a couple of weeks later, when both worms
and mud are easy to find.
Q. What do the robins do first upon arrival back on
their territories in the spring?
A. During
fine weather, male robins spend their time singing, investigating their
territories, and feeding. During cold or very wet weather, the males grow
more silent and concentrate on feeding and taking shelter in thick conifer
branches. Female robins investigate their territory, begin nest building,
and feed when they first arrive.
Q.
Why is the timing of robin migration so important?
A. In fall, robins wander and migrate when food is abundant but with a patchy
distribution. Their migration is irregular, allowing individuals to be
in a broad range so food is abundant for all. (If their migration was
more uniform, too many birds would be in one area at the same time, and
they would deplete the food there while other food went ignored. In spring,
the timing allows them to migrate right when worms are emerging and are
most conspicuous. And females return to their nesting areas when mud is
available so they can start nesting almost immediately after arriving.
Q.
What do migrating robins do during bad weather?
A.
If the robins have a reliable food supply, they hunker down near it, and
sometimes become very territorial, keeping other robins away. When not
actively feeding, they usually hunker down in a thick coniferous tree
to stay as dry, warm, and protected from wind as possible.
Q. What are some of the hazards that robins face on
their long migrations?
A. Being in so much unfamiliar territory, robins are more vulnerable to predators
during migration than when they are on a breeding territory. They only
rarely hit communications towers, because they migrate by day. During
the time that DDT was used, robin deaths usually took place during migration,
because DDT collected in robin fatty tissues in summer and in winter.
When the birds migrated, their bodies "burned up" this fat,
releasing huge amounts of the DDT into the robin's blood.
Q. How do humans affect robin migration?
A. When
humans used the insecticide called DDT in the U.S., many robins died during
spring migration as their bodies metabolized large amounts of body fat
at once--DDT from the worms robins ate all winter was stored in their
fatty tissues and all released into their bloodstream at once. This was
a harmful effect, and now that DDT is banned in the US, is no longer a
problem for our robins. Humans also have very positive effects on migration
by planting the trees that provide food and shelter for migrants.
Q. How do I tell the first robin of spring from the last robin of winter?
A. There is no one single moment when a robin changes from a wintering bird to a migrant.
Winter and migratory behaviors:
Feeding in flocks
Eating fruit
Flying in flocks
Getting along peacefully
Spring behaviors:
Running on lawns
Eating worms
Singing
Territorial battles
Carrying nesting materials
The problem is, one day an individual robin may be eating worms and singing, but if a sudden ice storm or other bad weather reappears (which happens a lot in early spring) that robin may again join a feeding flock and act like a winter or migrating bird for a few more days. So deciding whether a robin is a winter bird or a spring bird is a subjective judgment. We at Journey North consider a singing robin to be a spring bird, though we realize that sometimes surging hormones make robins sing even in winter flocks. In the majority of cases, robins really do wait to sing until they have reached their territory. Also, some singing birds in the vicinity of winter flocks are actually individuals that are not part of the flock, but have already claimed their territories. We've noticed that after the first robin arrives in some Minnesota backyards and starts singing, large flocks of robins will still be passing through for several weeks. Local birds sometimes seem to sing more often while these flocks are present in the area, as if to warn them that some territories are already taken.
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