It’s now mid to late October and migration is in full swing. You may have a handful of Warblers visiting for a couple of days. You may see an open field or marsh alive with thousands of birds. Or, migration may be a few Turkey vultures circling above as they catch a thermal heading South. It may be a single hummingbird heading for its winter home. You can see migration just about everywhere this time of year. On a calm, quiet night, step outside and you may hear the sounds of wings or the chirps of birds in the night sky. Fall migration is a busy, yet sad time of year for many of us. Yes, we lose many of our feathered friends.
Colorful friends with songs that bring smiles to your face. Sure we get winter migrators that help to liven up the winter landscape, but they aren’t as pretty and the songs seem to lack that certain something. As you may know by now, migration is a mix of internal stimulus dictated by the length of day or lack of daylight hours. This results in a feeding binge to put on fat to survive the journey and then the tendency for most species of birds to aggregate into flocks. Once the pre-migration flock is gathered, the feeding continues while the birds wait for suitable weather conditions. Something interesting is, some birds molt before migration, other birds molt once they reach there winter homes and still other birds like Barn swallows molt during migration. You wont see dust settling on swallows that’s for sure. They eat on the fly and have no time for a molt.
While the birds internal clock probably releases the hormonal triggers at a fairly accurate date each year. Though availability of food and the presiding weather conditions sometimes decide when the migration starts. For most birds, migration South is at a more leisurely pace than heading North. Birds stop to feed and rest, maybe make a few friends along the way. Robins for example may travel an average of 12 to 15 miles a day, or as needed. In my yard, White-crowned sparrows will hang out around here from two to four weeks before moving on. Most flights occur at between 600 and 5000 feet above sea level with an average height of 1525 feet. (Now how do they figure that out?) However, mountains may mean greater heights of several thousand feet.
Weather Influences Bird Migration.
If we had that ability to navigate, we wouldn’t need road maps or a compass.
Birds respond to weather conditions as well as light when deciding when to depart a summer or winter range.
An early spring with unusually warm temperatures can trigger early departure and early breeding. Likewise, extended bad weather or a cool spring can delay things.
Visa versa for fall travel.
Birds generally wait for good weather with favorable winds.
They avoid rain, overcast conditions, and winds that might blow them off course.
As a result, good weather triggers a wave of departures, with large groups of birds leaving at the same time and arriving at a stopover or destination together.
Most will stop to feed or wait out bad weather before moving on with another wave of migrants.
Climate and location also heavily influence fall migration for birds in the higher latitudes.
These birds arrive later, breed later, molt later, and leave later than the rest of the population.
Although most of our smaller birds make their longest flights at night, close observation shows travel is continued to some extent by day.
During the latter half of a migratory season birds may show evidence of an overpowering drive to hasten to their breeding grounds.
At this time flocks of birds maintain a movement in the general direction of the seasonal journey while feeding on or near the ground.
Sometimes they travel hurriedly, and while their flights may be short, they can cover an appreciable distance in the course of a day.
Scientists have been studying how birds find their way along these routes.
To successfully migrate from breeding grounds to winter grounds birds must be able to navigate (judge their position while traveling) and orient (determine compass direction).
Birds do this by using a variety of different cues which allows them to find their way in different weather and habitat conditions.
There are five main ways that birds navigate and orient themselves:
1) topographic features (things like mountains and rivers that can also influence wind direction).
2) stars. (the moon and planets differ each year and wouldn’t make a good guiding light).
4) earth’s magnetic field.
5) sense of smell.
Night migrators that use the stars to navigate have been known to spend the night if the sky is to cloudy.
Experiments show that most migratory birds have a built-in sense of direction and know innately which direction they need to travel.
First year Starlings in Europe kept in a covered cage and away from birds which have already migrated once or more, still move to the South side of the cage when the time comes for them to migrate.
Some birds appear to use landmarks and obviously at a height of several thousand feet they can see a considerable distance.
Here is another test.
Young crows born and raised in Alberta, Canada and then kept caged until after all the population had flown South and the first snows had fallen flew straight to Oklahoma where the rest of their flock was.
Some strong instincts there.
How about this test?
Is migration strictly instinct?
Mallards are migratory in Finland, but not in England.
Young hatched from eggs taken from English Mallards and put under Finish females had no problems migrating with the rest of the population.
No hard wire here.
For many species of birds, migration is indeed a learned thing.
the next time someone calls you a bird brain, thank them for the compliment.
Look at the survival instincts an adult bird has.
The biggest issues or dangers migrating birds do face are man made obstacles. Hundreds of thousand of birds die every year with in air collisions. Birds crash into sky scrapers, radio towers and guide wires. Now wind machines are becoming a big concern. Cities are now lighting up tall buildings to help out night flyers, but towers and guide wires are a different story. Often towers are built on remote hills and wind machines are being built in major flyways. Enjoy Fall Migration.
And how about the “GPS”?