Color-changing Birds, Fall Migration, and Lights Out Nashville
Decoding fall warblers and how to protect them on their big journey south
Written by Jenna Atma, Avian Biologist
As we near the end of summer, we also quickly approach the start of the fall migration season for many birds! Towards the end of August and increasing through September, millions of tiny songbirds will begin their incredible journey south towards their winter homes. For some, this may be as close as just a state or two away; for others, their southward migration may entail flying thousands of miles to reach Columbia, Brazil, or other Central and South American countries!
However, as these small migrants begin to pass through Tennessee, you may notice something different about them; many of these colorful birds somehow look more drab! Are they the same birds, and if so, how and why did they change colors?
Take a look at these two warblers we caught and banded at our bird banding research station at Warner Parks. Would you believe me if I told you that these two birds are actually the same species? These two handsome birds are both male Bay-breasted Warblers. They could even be the same individual! So what causes some birds, including many warbler species like the Bay-breasted Warbler, to change their plumage so drastically between summer and fall?
One reason for this change is because fresh feathers are better-suited for making the big southward flight. When birds are migrating, they need their feathers to be in tip-top shape to handle the long distance. Their very survival is depending on it! So after the breeding season is over, in the quiet late summer before migration begins, most birds will one-by-one drop their flashy “breeding” plumage feathers (which is called “alternative” plumage) and replace those feathers with new, duller ones (called “basic” plumage).
But this still doesn’t answer the question of why birds change their appearance. There are two primary reasons: more plain-looking colors can help birds camouflage with their environment better, and they also can take the extra energy it takes to grow intensely-colored feathers and use it instead to store fat on their bodies to survive the winter.
Color-changing warblers are an amazing phenomenon to look out for during fall-migration. Migrating such a long distance is an incredible feat, and it’s a massive challenge for birds every year to accomplish safely. That’s where YOU can help!
One of the biggest challenges for birds during migration is windows. Birds often can’t see clear glass or understand that it’s a danger, and especially during their nighttime migration, many birds end up colliding with windows believing they can just fly through to the other side.
On May 2nd, 2022, Mayor John Cooper Signed the Lights Out Nashville Resolution to help make Nashville a bird-safe city. Birds primarily migrate during the night, but are drawn to lit-up windows. Lights Out Nashville is an pledge where businesses and homeowners to agree to turn their building’s lights off at night, which helps prevent birds from being confused and drawn towards the brightly-glowing windows. Turning your lights off at night during migration can help save thousands of birds! Even small home windows pose a risk for migrating birds.
Another way to help prevent window collisions is to install window decorations to help make the clear glass more visible for birds. Bird Safe Nashville has a whole list of different and fun ways to make your windows more visible to birds, including window stickers, decals, shades/blinds, and even tempura paint projects for kids!
Help make your home safer for birds this migration season by turning lights out at night, or by making your windows more visible for birds, and go outside and enjoy spotting all of the color-changing migrants that fly past you on their big journey south!