The first Eastern Bluebirds of spring arrived on March 9, so we were out cleaning the 25 nest boxes that line the prairie trails in early March. It’s a good thing we finished on March 14, because the bluebirds started investigating the boxes immediately. On March 27, we saw the first Tree Swallows, and they headed straight for the boxes to check them out.
Tree Swallow nest in natural tree cavity (photo by Gary Shackelford).
In 2024, all the boxes were used. We determine how each box was used based on the structure and composition of the nest. We also have confirmation of our conclusions based on photo monitoring of the boxes (using a small light tube) throughout the summer. Eight were used only by bluebirds, ten only by Tree Swallows, three by wrens, and one by Black-capped Chickadees. Three of the boxes were used sequentially by Tree Swallows and bluebirds. If nest boxes are not available, Tree Swallows will sometimes use tree cavities created by woodpeckers or other holes in hollow trees.
The telltale sign of a Tree Swallow nest is often feathers. In some cases, there are so many feathers, you can’t even see the underlying nest structure of dry grass or pine needles.
Tree Swallow nest in nest box, complete with lots of feathers (photo by Gary Shackelford).
Observations of Tree Swallow nests going back to the early 1900s note that feathers are a regular and important component. They are arranged with the quills placed in the grasses of the nest base so the tops of the feathers curve over the nest. The feathers are not from the swallows themselves. White or light-colored feathers are preferred, often those of domestic waterfowl, chickens, or gulls. In our sanctuary, none of those sources are available. Instead, we find feathers from the likely nearby resident birds—Wild Turkeys in the prairies, Sandhill Cranes in the vicinity of their own nests, Wood Ducks and Canada Geese near the wetlands. One of the boxes even contained several large white feathers—it was located under the Bald Eagle nest!
Though many studies have documented the feathery feature of their nests, the reason for their use remains uncertain. The feathers are usually added after egg laying begins. A strong possibility for the practice seems to be a thermal advantage—to keep the nestlings warm. There are data showing that in nests with a lot of feathers, the young grow faster. Other hypotheses are that the feathers shield the eggs or nestlings from the view of predators, or they signal to other Tree Swallows that a box is already in use—a quick peek through the entrance quickly makes this clear.
A real treat for the patient observer is to watch the Tree Swallows as they appear to play with feathers. This may even be a part of pair bonding. The male, who usually collects the feathers, may drop a feather from the sky rather than bring it into the nest. The female will then swoop in and catch it on the way down. The pair may repeat this behavior multiple times, creating an aerial dance. At other times, “aggressive” chases for possession of feathers occurs. A bird may bring a feather into a box and then come back out with it and continue the chase. If others don’t seem to be paying attention, the bird will drop the feather, attracting attention and initiating a chase. Feather chases may even occur in the fall well after nesting is over (Birds of the World).
If you enjoyed this feature about feathers, I hope that you will consider placing (or monitoring!) nest boxes for cavity nesters in search of a home.
Written by Penny Shackelford, Fair Meadows Sanctuary resident manager
Cover image: Pair of Tree Swallows male on the left, female on the right (photo by Gary Shackelford).
