Bird Watcher's General Store

“A Cape Cod Destination Icon For 40 Years”

Tree Swallows

Dear Bird Folks,

Whenever I go for a walk I see lots of Tree Swallows. They are all over my state. (I would take them over any other bird and I think they would take me over any other human.) Please tell me why I see so many Tree Swallows.

– Ian, age 11, 5th grade, Jamestown, RI


Good for you, Ian,

In spite of all the gloomy virus news, it’s great to hear that you are still going outside and appreciating nature, which is the best way to ride out a pandemic. Also, I enjoyed reading your letter. I think the only letter I wrote when I was in the 5th grade (and this is true) was to Ringo Starr. (Ask your parents, or maybe your grandparents, about him.) That was an awfully long time ago and, you know, I still haven’t heard back from Ringo, but the mail hasn’t come this morning. Maybe today’s the day.

According to Mass Audubon’s most recent breeding bird survey, the Massachusetts Tree Swallow population is “nearly ubiquitous.” So, it appears these swallows are “all over” my state as well. There seems to be three major reasons for their breeding success. They have a balanced diet, plus they have taken advantage of something that humans are doing and are reaping the benefits of something that humans have stopped doing.

Most other swallow species (Barn Swallows, Purple Martins, etc.) are totally dependent on insects for their survival. As you probably know, swallows hunt by swooping through the air and catching flying insects on the wing. A stretch of cold, rainy spring weather, which prevents insects from flying, can be devastating for hungry swallows that have just returned from the south. Tree Swallows, however, enjoy a more flexible diet. They have the ability to switch from bugs to berries, particularly bayberries, when things are tough. The first Tree Swallows I saw this year arrived in late March. The weather was pretty ugly back then and these birds would have been in trouble if it weren’t for their ability to find alternative food sources.

In addition to not being fussy eaters, something else has helped the Tree Swallow population grow…humans. One of the first bird books I ever bought was the Peterson Guide to Bird Nests. When I read the account of Tree Swallows, I was surprised to see that the book specifically mentioned my home turf of Cape Cod. According to the author, the placement of ninety-eight man-made birdhouses quickly increased the area population of swallows from a mere four pairs to sixty. Why did the boxes help so much? Tree Swallows may have a flexible diet, but their nesting needs are rather particular. Unlike robins or cardinals, which have the ability to build a nest wherever they choose, Tree Swallows are tied to trees, more specifically, tree cavities. Swallows are talented flyers, but their carpentry skills are minimal (kind of like mine). They are totally dependent on finding holes in trees previously created by other birds, mostly woodpeckers. Unfortunately, woodpeckers don’t always live near the open fields that the swallows love so much. This is why the birds were thrilled when some kindly Cape Codder set out boxes in preferred swallow habitat. (No, that kindly Cape Codder wasn’t me, but I do have a swallow box in my yard. More on that later.)

For some barbaric reason, people used to think it was cool to trap wild creatures, peel off their fur and turn it into hats and other garments. Happily, that gross custom has faded. No animal has benefited more from this fashion change than America’s hardworking beavers. More beavers mean more beaver dams and more dams mean more beaver ponds. Beaver ponds create instant habitat for all sorts of living things, except trees. Trees caught in the rising water quickly die, which sounds bad, but don’t tell that to the woodpeckers. Woodpeckers love to create nest cavities in dead or dying trees. And what birds are ready to move in when the woodpeckers eventually move out? That’s right, the Tree Swallows. Thanks beavers.

Over the years my little suburban backyard has had nesting chickadees, Carolina Wrens, Great-crested Flycatchers and even screech-owls. But this year none of those birds are using my boxes. (They’ve probably gotten tired of listening to my neighbors’ barking dogs and 24-7 leaf blowers.) Fortunately, “my” Tree Swallows don’t seem to mind the noise and have returned for another breeding season, and are a welcomed sight (just like your letter). As soon as the birds arrived, I put out a few white feathers (swallows love white feathers) and the female quickly scooped them up for her nest. After working on her nest for a while, the female would often sit and peer out of the entrance hole of the birdhouse. With her dark head and white chin, it looks as if she is wearing a protective face mask, which is so appropriate right now.

If you are seeing a lot of Tree Swallows now, Ian, just wait until fall. Each September swallows gather by the thousands along the coast in preparation for their journey south. I’ve run into these flights on several occasions and it’s an amazing experience. Hopefully, you’ll come upon one of these huge flocks yourself someday. In the meantime, thanks again for your nice letter. Speaking of letters: I just heard the postal carrier drop off my morning mail. Perhaps this is the day I’ll finally hear back from Ringo. If he mentions anything about Tree Swallows, which I’m sure he will, I’ll let you know.