An Unusual Purple Martin Nest. - Stan Kostka, Western Purple Martin Working Group
Purple Martins have been described as obligate secondary cavity nesters. Their use of birdhouses, and other manmade and natural landscape features as nestsites is well documented. In recent years, in addition to pursuing martin conservation and research activities using nestboxes, I have observed, and become quite fascinated with, pairs of martins using incidental nestsites in or on various manmade structures. The steel and concrete box girder bridges of Sacramento are a good example, as are spaces under piling caps, rot pockets in the ends of horizontal timbers, ledges under piers and on navigation markers, and in the ends of horizontal pipes, to name a few. In my experience, up until the end of the 2002 breeding season, all these incidental nestsites shared a common component, also found among the elements that form a nestbox (or gourd), namely a roof, i.e., some physical barrier between nestcup and sky.
In the summer of 2003, on 14 July, while banding at a colony that in 2002 had been comprised of 16 pairs, 15 in nestboxes and one in a capped piling cavity, I was surprised to see a martin exit a second piling cavity nearby. The upper part of this piling was hollow, and had no top. By standing up on the seat of the boat at high tide, I was able to look down inside the piling. There, just beyond my reach, were the young of pair 17. The adults were accessing the young via a hole in the side of the piling, about a foot above the nest. The nest contained three young, about a week old, the only martin nestlings in my experience, with a view of the daytime and night skies directly overhead their nestcup. On July 24 while doing more banding at this site, a cordless circular saw along with some hand tools were used to make a small access door in the side of the piling, opposite the entrance hole. Those three nestlings became Orange left, A460 thru A462. The improvised access hole was then sealed. The nestlings were still there on July 31, during my last banding visit to the site, apparently getting ready to take on the world at about 24 days old. I never saw them after that date, and with the weather remaining dry and warm for some time afterwards, I recorded them as successfully fledged for 2003.
As with all experiences unique to our own personal observations, it seems reasonable to assume that similar events are occurring and have occurred elsewhere. Since martins commonly use abandoned marine pilings as nestsites throughout their Northwestern range, this “roofless” nesting cavity is likely not the only one of its kind. Nonetheless, I consider this record noteworthy, in that it clearly expands the definition of what up until this point, was generally considered a suitable nesting cavity for Purple Martins.