Sunday, December 23, 2012

Closer look at birds that fly south and those that are migrating north

I’m excited about seeing all these new finches from Canada this winter! I’m keeping my feeders full so I can watch all the activity. Will they stay around because they have such a good thing down here or will they leave in the spring?

What a wonderful question! I wrote earlier about how this was going to be a good season for bird watching because Canada’s natural seed crops were horrible this year and lots of birds that usually like to winter further north are going to have venture south to Michigan to find food.

Those hardy Canadian birds that irrupt occasionally are wonderful to observe but generally heed their hormonal urge to leave in the spring when it’s time to nest. So enjoy them now.

On the other hand studies have revealed that more and more southern birds are moving north and sticking around mid-Michigan in the winter. Land development, a steady increase in global temperatures, and bird feeding during the last half of the 20th century may have played a small role in the northward expansion of some southern birds.

For example, the northern edge of the Cardinal’s range has expanded greatly since the days of John James Audubon. Originally a southern bird, the Northern Cardinal began expanding its range into northern states around the 1900’s. After nesting season Cardinals stop defending territories and begin to flock together. During the early days of their expansion they would migrate back south during the winter. But in time they became year round residents of Michigan.

The Tufted Titmouse has also been expanding their range northward since the 1940’s and is now found even in Canada. Speculation for their expansion includes warming winter temperatures and the increase in mature woodland habitat.

Or take the Turkey Vulture. Once only a southern US bird, by the 1960's they had extended their breeding range into Michigan. The popular theory is that the interstate highway system increased the availability of food in the form of roadkill.

So what do we make of all this? How do animals know when and where to go? The usual explanation is that the migration is driven by instinct, hard-wired into birds. But birds might be evolving. Whether or not a bird flies south for the winter depends a lot on what food the species eats.

Every year we get more and more sightings of orioles, hummingbirds and other birds that normally migrate, sticking around. Amazingly, if a bird can get enough food, it apparently can survive even the worst weather.

That’s why information gathered from the citizen science projects like the Great Backyard Bird Count, along with observations from the Christmas Bird Count, Project FeederWatch, and eBird, helps to us see the “big picture” about what is happening to bird populations. The longer data is collected, the more meaningful it becomes in helping scientists investigate far-reaching questions, like:

• How will the weather influence bird populations?
• Why winter finches and other “irruptive” species appear in large numbers during some years but not others?
• How will the timing of birds’ migrations compare with past years?
• How are bird diseases, such as West Nile virus, affecting birds in different regions?
• What kinds of differences in bird diversity are apparent in cities versus suburban, rural, and natural areas?

For highlights of past results, visit http://www.birdsource.org/gbbc/science-stories

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