Nest-Building Tree Swallows

Tree Swallow

Tree Swallow

Now that June has arrived migration is dwindling to a close and the breeding season has begun in earnest. I spent some time at Hurdman Park at lunch on both Monday and Friday, eager to see what new birds have arrived and whether any migrants were still moving through. On Monday, June 2nd I found the first Yellow Warblers, American Redstarts, Gray Catbirds and Red-eyed Vireos singing on territory. At least five Warbling Vireos, a Least Flycatcher and Eastern Kingbird were also present, and I heard an Eastern Wood-pewee singing in the woods close to Highway 417….the first one I’ve ever heard at Hurdman. It was likely a migrant, as pewees prefer wooded areas that are not adjacent to human habitation, and the woods at Hurdman are a small forest oasis in the middle of a bustling city. Not surprisingly, I didn’t hear the pewee on my visit on Friday or any other subsequent visit.

I also saw my first Baltimore Oriole at Hurdman on Friday, a lovely male singing high up in the tree tops near the bike path. A large flock of European Starlings was also present, and many of the three dozen birds were recently fledged youngsters. I could hear the young starlings begging for food and saw a few following their parents in the grass at the side of the bike path. When I passed by, over 30 starlings flew out of the grass, the cautious adults followed by their brown, squawking offspring.

As I followed the bike trail I noticed a single Tree Swallow perching on one of the signs. This is an unusual sight at Hurdman; though I sometimes see large numbers of swallows foraging over the area in the spring, they are always in flight – never perching, especially this close to the ground.

Tree Swallow

Tree Swallow

This is a male based on the rich blue colour of its head and the thin black eye mask; females are duller with more brown in their upperparts.

Tree Swallow

Tree Swallow

I soon saw the reason why this Tree Swallow was sitting there so vigilantly. His mate was close by, gathering dried grass as nesting material. Female Tree Swallows do most of the nest-building, which takes a few days to two weeks to complete. Although nests are built almost entirely from grass, swallows sometimes use pine needles, moss, aquatic plants, animal hair, and man-made materials such as cellophane or cigarette filters. The material is usually collected from the ground close (within 100 feet) to the nest site. The finished nest consists of a cup about 2–3 inches across and 1–2 inches deep, lined with the feathers of other bird species.

Tree Swallow

Tree Swallow

I watched to see where she would take the mouthful of material, and was surprised to see her using an opening in a metal structure. Tree Swallows are cavity nesters and are more likely to build nests in dead trees, though they are known to nest in hollow stumps, building eaves, Wood Duck nest boxes, holes in the ground, old Cliff Swallow burrows, and other unconventional sites.

Tree Swallow

Tree Swallow

The location was well away from the bike path, but close enough to the Transitway (the road used by the buses) to be of concern. Still, this was the first time I’d seen a Tree Swallow gathering nesting materials in the “wild” (that is, away from any of the well-known nest boxes around Ottawa) and it was thrilling to observe the female take the material to the nest and return to gather more while the male looked on.

Although individual Tree Swallows may have the same mate several years in a row, it is believed that they are probably faithful to the nest site rather than the mate. They are not very faithful and often mate secretly outside the pair. Males have even been documented attending two mates in separate nest sites!

It will be interesting to see whether the Tree Swallows remain at this site, as I am not sure whether the metal structure they built their nest in is used for anything or checked by maintenance workers. It would be nice to come back later in the summer and see them feeding their young!

Author’s note: When I returned on June 9th I saw at least one swallow foraging over the field near the nest site. I didn’t visit Hurdman again until August 7th – two months later – and didn’t see any swallows then, or after that date. Whether they remained at that site or raised any young is unknown.

– September 20, 2014


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