by Sarah Belles
Recently, I had the pleasure of going birding at Brazos Bend State Park with friends. One of our first sightings of the day was a flock of what had to be at least 500 tree swallows congregating on a small lake. Some perched on vegetation emerging from the water, while others swooped and glided over the surface. Large gatherings of tree swallows are not an uncommon site near the Texas coast in the wintertime, especially in marshy areas or fields near bodies of water.
Tree swallows are small, roughly sparrow-sized songbirds. The males are a beautiful blue-green color on their upperparts with a black face mask, while females tend to be more of a drab brown with some blue-green. Both males and females have white underparts and white crescent shaped marks on their sides near their rumps. Their wings are long enough to reach the tip of their tail when perched, and their tails are fairly square, sometimes having a slight notch.
Like other swallows, tree swallows are mostly insectivores. They tend to prefer areas near water since those spots usually have abundant aquatic insects. If you watch tree swallows in flight, you can see their impressive acrobatics that they use to catch insects in the air. You might also catch a glimpse of one skimming the water and shaking off to clean itself. In the winter when insects are less plentiful, tree swallows enjoy bayberries as an alternate food source.
In the spring, tree swallows will begin migrating north for the breeding season. They usually show high breeding site fidelity, or in other words, they tend to return to the same location year after year to breed. Here, they will pair up and make their nests in abandoned tree cavities made by woodpeckers or in man-made nest boxes. Inside the cavity or box, the swallows will create a grass cup lined with feathers. Feathers not only serve as a soft, warm nest lining, but also can play a part in the mating ritual. A tree swallow will take a feather in its beak and play chase with another swallow or will drop a feather to see who can catch it first in midair.
Predators of tree swallows include birds of prey such as kestrels and merlin, who are also impressive aerial acrobats. Other predators include small mammals and snakes. One advantage birds gain by congregating in large flocks is protection in numbers. Tree swallows have chattering alarm calls and will come together to swarm and dive bomb predators.
Tree swallow populations are not of concern at the moment, but have shown a general declining trend throughout the years. One big issue is the removal of trees with cavities essential for nesting. People who live in the breeding range of tree swallows can help mitigate this by constructing properly sized nest boxes with predator guards. Another problem that insectivores in general can face is pesticide accumulation in their bodies from the insects that they feed on. As with many other bird species, climate change also seems to affect tree swallows, especially with the timing of egg laying.
Photo Caption: A flock of Tree Swallows congregate at a lake in Brazos Bend State Park. Photo by Sarah Belles.
