AMERICAN GOLDFINCH: Adapting for Survival & Late Summer Nesting

WILDER SIDE OF OAKLAND COUNTY

IMG_6932On a desert island in the heart of the Galapagos archipelago, Darwin received his first inklings of the theory of evolution by observing the variations of finch beaks. His awareness led to later confirmations that through the process of evolution and natural selection, species physically change and adapt to the landscape they inhabit. This endless process of evolutionary change, or survival of the fittest, continues today. (The Beak of the Finch by Jonathan Weiner presents an exciting and compelling modern day look back at the process of evolution, a process that is neither rare nor slow and is never ending.)

Fast forward almost 200 years to Oakland County and the American Goldfinch of today.

Individual variability both in appearance and behavior of our native goldfinch, the American Goldfinch (Spinus tristis), is in full display now as their nesting season surges forward. The American Goldfinch is the only finch that molts it’s body feathers twice a year and it is also one of the last birds of Oakland County to breed. Although the males sang with great exuberance all spring to attract mates and define their territory, it was not until late July that nesting began. Some will still be nesting through early September.

These beautiful birds are very much at home in our midst and, just like back in the Galapagos, there are differences in individuals. The molting and coloration differences are obvious, while the behavioral differences are more subtle, and have accelerated the natural selection process.

I live in Brandon Township, not very far north of Independence Oaks County Park, an incredibly productive habitat for the American Goldfinch. Whenever I approached a finch near the wide open brush-y meadows  at Independence Oaks it  would take flight quickly.  But just a few miles north, almost adjacent to my meadow clothesline,  I noticed a difference in their behavior.

I went to hang clothes at the edge of my meadow and noticed a flash of color in shrubs barely 10-feet away from the line. Then I noticed the nest partially hidden by leaves, and firmly placed between three branches of a very young black walnut tree.  I walk by that tree several times a day and have come to realize that ‘my’ goldfinch accepts me as part of their surroundings and in all likelihood, they know my wanderings and behavioral ways better than I know theirs. I do know this: when those hatchlings peer out of the nest and see me, they too will accept me as the norm. And in all likelihood they will have no issues selecting similar, close to human activity nesting sites next year. That is adaptation and an opening for natural selection.

Information provided by the Cornell Lab of Ornithology gave me more insight into their behavior and habits. As for their seemingly late nesting, I discovered it coincides with the abundance of seeds they favor, and high on that list is thistle.  The acrobatic finches are almost exclusively vegetarian and are masters of touch-and-go landings on the thistles. They fly back to their nest with thistle seeds in their crop and regurgitate for their huge-beaked hatchlings; and their nests are another example of adaptive behavior timed perfectly for their habitat.  The nests are tightly woven and include spider silk, fall webworm caterpillar webbings and fine strands of fiber from thistles.  I wonder what Darwin would think if he could be a silent observer of the finches on the wilder side of Oakland County.

“And for myself I am fully convinced that there does exist, in Nature, means of Selection, always in action and of which the perfection cannot be exaggerated.”   Charles Darwin.

Text and photos by Jonathan Schechter, Nature Education Writer for Oakland County Parks. Visit DestinationOakland for information on all 13 Oakland County Parks.

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