Tuesday, June 25, 2013

Blakeman on bridge-nesting Barn Owls and a PS

photo below of a Barn Owl courtesy of en.wikepedia.org
In regard to my post of June 17th, about the Barn Owls nesting on the Verrazano-Narrows Bridge, raptor expert John Blakeman sends an informative note:

I found the article on the Barn Owl nest in the Varrazano-Narrows Bridge interesting for two disparate reasons.
Barn Owls, as mentioned, need expansive areas of herbaceous habitat over which to hunt; searching for voles and mice, which sustain them. Clearly, there must be some large expanses of drier wetlands or meadows near the bridge.
But with the nest, I have a concern that the bridge officials must consider (if they haven't --- their engineers probably have).
Barn Owls excrete large amounts of uric acid, the white component of bird feces. The owlets will annually coat the cavity with layers of this material --- which does not chemically abide well with structural steel or paint.
In short, this and other such cavities in the bridge will have to be screened off, prohibiting future owl nestings. Should this be overlooked, it's but a matter of years before normal atmospheric humidity and precipitation create a very corrosive fecal goo that will literally consume the structural steel --- not an outcome that bridge travelers might wish to consider.
Yes, peregrine falcons excrete the same uric acid at their bridge aeries; but in most cases such nest sites are in the open, where normal rains and storms wash away most of the excrement before it can cause corrosion. Or, proper nest support structures have been installed, that segregate the feces from the structure.
In the case of the Barn Owls at this bridge, it would be best to construct and attach a dedicated barn owl nest box (made of wood) near the existing cavity. Upon the closure of the cavity (best in autumn), the owls most likely would resume nesting in the new nest box next season, thereby preserving the metallurgical integrity of the bridge, and the reproductive capacity of the resident owls.
I can provide barn owl nest box construction details, should anyone be interested.
John A Blakeman

PS from Marie:

I'm off to France and [briefly] Spain tomorrow. I'll be back after July 4th. Hope your holiday is great!