Summer is swallow season. Spring migration can in some ways seem like a less dramatic affair than the fall migration of ducks and shorebirds in California, with a relatively subtle arrival of songbirds, many of which slip into the woods where their presence may go unnoticed by ordinary people. I think if there is one exception to this trend, all summer birds that anyone can easily observe are swallows.
Swallows are a family of songbirds that evolved to be optimized for flight and aerial foraging. All have a distinctive shape with long, pointed wings, short legs, and rounded heads with small beaks but wide mouths. This shape enables their feeding method, spending many hours a day on the wing as they catch airborne insects.
Another consequence of their skillful and efficient flight is that swallows are prolific migrants, with many species traveling far into South America, making longer migrations than most of our summer songbirds when they visit us from March around August. Beyond the biological implications, the flight skills of swallows are what grab our immediate, first-hand attention. They are incredibly fast and agile, and more inherently airborne than almost any other bird. Look at them !
I’d like to tell you at least a little about our four most notable swallow species here in Marin: the mud-nesting rock and barn swallows, and the tree or nest-box swallows and the purple-green swallows that nest in the the nest boxes. The less common purple swallows and the easily overlooked northern rough-winged swallow complete our local selection.
Cliff swallows are perhaps the easiest to notice, as they nest in large colonies in areas of frequent human proximity, including on bridges and overpasses. The man-made “cliffs” created by our structures provide them with a relatively safe place to place their nests made of mud, saliva and plant matter. Cliff swallows are one of the birds most similar to us in their social spacing, with each family having its own confined area for the immediate occupancy of the incubating mother and then the chicks, but with other neighbors at proximity. You can recognize cliff swallows by their dark blue, metallic backs and headdresses that show off pale rusty patches on their rump and forehead.
The barn swallow belongs to the same general lineage of mud-nesting swallows. In fact, mud-nesting is the norm among world swallows, and barn swallows are the most cosmopolitan member of the family. They are found all over the world. Barn swallows migrate from Africa to Europe and from Australia to East Asia, just as they do from South America to Marin. You can read about them in “Virgil” and then see them nesting under the eaves of See’s Candies.
Compared to cliff swallows, barn swallow nests are more solitary than found in colonies. And although they share a general color scheme of dark blue above and pale brown below, barn swallows are easily distinguished by their lack of a pale rump and their deeply forked tails. (Our other swallows all have relatively flat tails.)
Our last two notable swallows, the Tree Swallow and the Violet-Green Swallow, do not build mud nests. Instead, they build their nests in tree cavities or in nest boxes that replicate those cavities. The two are relatively close relatives and can collectively be considered our two “white-bellied swallows”.
Tree swallows are the most common species on the continent and are brilliant blue on their backs and crowns. Violet-green swallows are green on the back and can also be identified in flight by a more noticeable white patch on the rump. Overall, these two species share many habits, but tree swallows tend to nest reliably near water, while violet-green swallows can nest in fairly dry environments in oak forests.
Speed and distance have lost some of their thrill and sparkle in the age of cars and planes, but they are still extraordinary things from the perspective of our human bodies. But imagine there are no engines. Rediscover the wonder of a slow-paced era. Compare the flight of swallows to the trampling of your feet and feel our weight of lead.
Swallows are the summer’s gift of speed, of vast distances traveled and movements too fast to follow, of a life above our heavy Earth.