Why Some Birds Fly South for the Winter and Others Do Not
The Coming of Winter
In the northern reaches of the United States, just before the leaves start to fall, birds begin to flock together and prepare for their annual migration south. Birds that we usually see alone or in small groups during summer months will gather with others of their kind, or often with those of other species. Waterfowl will congregate and form that well-known V pattern in the sky as they journey to warmer climes.
American robins vanish, not to return until the spring, reminding us that a long, cold winter is bearing down on us. As ominous as the dirge of some death knell, when the birds start to leave we know the sweet warmth of summer is but a memory.
But not all birds fly south. Some remain through the snow and the cold, and some species are even more abundant during the winter months. Why do some birds fly south while others stay put? Why do some appear to thrive in the snow? When birds migrate, where do they go, what do they do, and how do they decide when it’s time to come back?
And how the heck do they know where they are going?
These are some of the things I ponder each winter as I watch the little black-capped chickadee dart around my birdfeeder, and wonder where the rose-breasted grosbeak has gone. So let’s find out why birds fly south for the winter!
Why Do Birds Fly South?
It seems logical that the reason many birds spend the winter months in more pleasant, southern locations might have something to do with the warmth of the sun. This isn’t exactly the case. Birds can and do survive extremely harsh winters. Like most migratory animals, the primary reason for moving is food.
In the summertime, food is abundant in northern climates because insects are active and plants and trees are flourishing. When it comes time to breed, birds want to be where they have the best shot at finding food for themselves and their chicks. When it becomes difficult or impossible to find food, it’s time to go to warmer climates where food is still plentiful.
For example, in northeastern states, the American robin will arrive in the spring and leave sometime in the early fall. Robins eat worms, beetles, grubs and other such insects, which they aren’t going to find in the cold and snow. You’ll never see a robin at your bird feeder; they will not eat foods that sustain some other birds. They need to fly south, or they will starve.
Ducks, geese and other waterfowl are other good examples. Their lakes and ponds freeze, making it extremely difficult to survive in their intended environment. To find adequate food, escape predation and maintain their healthy quality of life they’ll move on to warmer climates. They fly in that V pattern to conserve energy, and to improve communication between birds. However, sometimes waterfowl are known to overwinter in cold climates when they are overfed by humans.
How do birds know when it is time to fly south?
So, this tells us why birds fly south, but how do they know when it’s time to go? Does a bird make a conscious decision to fly south? Do birds “follow the food” like some of the migrating animal herds of Africa?
Sort of. Scientists say birds likely have an innate response to the reduction in daylight hours, signaling to them that winter is near and they’d better get moving. This is why, no matter how much you stock your bird feeder, many bird species are going to head south just the same. The exact day they start their journey will be influenced by local weather patterns, but it is the daylight that gives them the signal to migrate.
Why Do Some Birds Stay Through the Winter?
Some birds don’t seem to mind the winter. The black-capped chickadee, northern cardinal, blue jay, tufted titmouse and others will brave the most brutal cold and snow. Feathers are pretty good insulators, and most birds could make it through a harsh winter if they had to.
So if bravery isn’t the reason birds stay through the winter, what is? Again, the reason is their diet. Some birds don’t need to rely on the plenty of summer. They can forage for insects in the bark of trees and find enough food to make it through the cold, dark months. In fact, in some areas, even the American robin is known to stick around through the winter months, if it can find enough food.
Other birds actually become more plentiful in winter. The dark-eyed junco is an example of a bird that will happily inhabit areas other birds have vacated in the winter months. In the Northeastern United States, Juncos will move down from their breeding grounds in Canada to overwinter in a comparatively milder climate.
If a bird is of a species that can find food in the winter, it has no need to migrate. Well-stocked bird feeders may help some species during periods of exceptionally harsh weather, but otherwise, the birds that stay through the snow and ice will know how to find enough food to survive.
Where Do Birds Go When They Fly South?
When the birds leave the northern states, where do they go, and how do they know how to get there? Many migrating birds find their way to Mexico or Florida, overwintering in tropical climes. Others simply need climates where the food is abundant enough to sustain them.
How do migrating birds know where they are going?
Remarkably, birds seem to possess innate knowledge that helps them to negotiate their long migrations. They are believed to navigate by the sun during the day, and the moon and the stars at night.
There is also some research that says they are aware of magnetic fields in the earth and use them to find their way. It’s a kind of internal GPS, and one of the more impressive abilities in the animal kingdom.
The next question is one you may ask of people who move to Florida in the winter: Why do they come back? Of course, we can't speak for the people, but for the birds, again, it’s hardwired into their systems. When daylight hours begin to lengthen, birds know it’s time to come back to their breeding grounds.
Like many animal behaviors, the whole ordeal is naturally designed to facilitate the survival of the species through procreation.
The Amazing Bird Migrations
Birds are everywhere. They’re easy to take for granted, but they really are wonders of nature. The deeper one digs into their behaviors the more interesting they become. This article dealt with North American birds, but there are some amazing bird facts from around the world.
For example: Did you know the bar-tailed godwit migrates from China to New Zealand in one flight, a distance of over 5,500 miles?
Now you know a little more about why birds fly south, what they do when they get there, and why some are brave enough to stay through the winter.