| |
To Fly South or to Stay Put? This is the REAL Question!
I am driving along highway I-494 in Bloomington and see a bird with their wings set---getting ready to land after a flight from “who knows where.” It is a peregrine---which one exactly, I am not sure, but it brings a question to my mind---what determines whether a bird migrates or not?
With some species of bird, this is a simple question with a simple answer: “This is Minnesota, and in the winter it gets cold: my food disappears and as a bird that eats worms and other insects, I must fly south.” However, to a peregrine living in an urban area such as the Twin Cities, this question isn’t so easily answered. We have known for many years that some birds migrate from their nesting  territory and others stay year round. We don’t have an easy answer though for why this is. For example, we have some individual birds that migrate some years and in other years, don’t. WHY? Is it weather? What about food supply? What about genetics? What about that “migration urge?” Does migration behavior lessen a bird’s ability to maintain possession of a territory? Or does previous possession of a territory have a greater influence than migration on continuing to be able to possess a territory the following year? If you migrate and, upon return, lose your territory to another bird, would you stop migrating in the future if you gain another territory? Is it a combination of two things in particular or maybe all of them to some degree?
This question is something I am trying to look at a little bit deeper. For example, I am looking at all of the urban birds in the Mpls./St. Paul area this winter. I have the genetic information on all of the banded adults to help me determine if they are of a subspecies of peregrine that might be more or less migratory. I also have all of the weather information to look at to compare from year to year to determine possible influences. And I have  observational data on several sites for the past three years that identifies whether the individual bird has migrated or not. I am also working with a professor at the University to help me with all of the “significant statistical stuff” to say I could be on to something, or it is just chance and who really knows. Either way, I am getting an opportunity to continue to learn something and just maybe, shed some light on a difficult question. I know three or four years of observations can’t be a sure-thing, but it is a start.
Back to Field Notes.
|