Many swallows are named after their preferred nesting sites. Barn Swallows, for instance often chose the overhanging eaves and beams offered by barns and Bank Swallows operate out of holes tunneled into sandy banks. These names are only suggestions, however, and none of these birds are required to follow their restrictions. Cliff Swallows, in the absence of natural precipices will build their mud pottery structures on the stone-like substructure of bridges and overpasses. Barn Swallows are equally open to the support beams on docks. Bank Swallows will not switch to 5/3rd Banks. Swallows refuse to pay interest on rental property.
Tree Swallows, to continue on this theme, are closely associated with tree cavities. These green and white birds frequently use old woodpecker holes and are often the first tenants to move into a newly vacated Downy Woodpecker home. They will readily take to man-made “tree” cavities as well. Bluebird houses really should be referred to as Tree Swallow houses- given the number of these birds that take up residence in them.
Although wood cavities – either man-made or woodpecker made – are the preferred housing material there are further exceptions. At least one local pair of Tree Swallows have gone trailer park. These birds have opted for the metallic confines of a parked boat trailer for their nest hole.
When I saw a swallow dive into the open end of a boat trailer support last week I thought the bird might be doing some creative exploring. They will often check out a number of false leads. (Just the other day I watched another pair scoping out the exhaust pipe on a car. The female was peering into the pipe as the male sat on the ground nervously looking about). When the trailer swallow flew off I took the opportunity to look into the depth. Sure enough, there was a wad of nesting material about two feet down at the point where a cross beam intersects the angled slope of the upright (see above). It was a nest site.
This particular bird posed a bit of a problem at first. Unlike the typical iridescent green/blue of the species, it was brownish and appeared to have a dusky stripe across her chest in the manner of a bank swallow (see above). Even terribly misguided Bank Swallows don’t nest in man-made structures, so this seemed unusual on two levels. The problem was quickly solved when a perfectly normal looking male Tree Swallow showed up and perched outside the trailer nest. Even terribly misguided Tree Swallows don’t take up with Bank Swallows, so the brown female was, in fact, a first year female Tree Swalllow.
Perhaps it was the inexperience of the female that led here to chose such an unpromising location. The open end of the trailer tube was angled up to the weather and nothing seemed conducive to success. I returned later in the week, expecting the place to have been wisely abandoned, only to discover that the nest was now fully lined with feathers and the female was incubating eggs. They were giving site No. 175 a chance.
Tree Swallows – actually all swallows as far as I know -use feathers to line their nest. They do not use their own, but seek out large light-colored duck, chicken, or heron feathers (whatever the nearest source might be). The Barn Swallows building their nests under the nearby docks do the same thing and I captured on of these fellows in the act (see here). The pale brown female Trailer Swallow sat patiently as I observed her through the top of the tube. She flew off on her own after I backed away and this allowed another peek at her clutch of fragile white eggs (see below). Both parents dive bombed me during this attempt so I backed off and left them to their own.
I just checked Trailer 179 yesterday and the birds are still at it. She was so deeply surround by feathers that I failed to see her nestled within their folds. When she left I was unable to see whether the eggs had hatched (it takes around 14 days) and chose not to stick a probe down the tube and disturb things anymore than I already had. One large heron feather was arched over the spot.
Fortunately the boat trailer will be parked in its present position for some time (the owner has his boat in the marina for the summer). The nest is in no danger of becoming a mobile unit. We can safely watch the progress of these Trailer Swallows through to the end.