What a contrast! A week ago yesterday, 4/16, we gloried in record high temps in the 80′s. Yesterday and today, 4/23 and 4/24, we got our share of the April “Noreaster” that hit large areas of the northeast. Yesterday was in the 30′s with rain and wet snow, and today hasn’t been a great deal better, with 40′s, intermittent rain, and cold gusty winds. As mentioned before, this nasty combination forces Tree Swallows into full survival mode. Box claiming and nest building are forgotten temporarily in the struggle to find food and stay warm. And it’s under conditions like these that little box design refinements may mean the difference between their life and death.
I stayed completely away from the grid yesterday. I knew there would be no swallows in the field outside the boxes but there might just be clusters of swallows inside one or two boxes, roosting communally to conserve heat. I’ve seen this in the daytime before, and the last thing I wanted to do was disturb them if this was the case.
Today, 4/24, I did venture out to the field, both in the morning and again in the afternoon, but I saw no Tree Swallows perched or flying. They were either communal roosting or foraging elsewhere over some secluded backwater. I didn’t check boxes for fear of disturbing a roosting cluster. And, as at other many times over the past ten years at Salmon Creek, I was thankful our project’s boxes are made to be snug and dry inside.
Nest box design should take local microclimate into account. If you manage for cavity-nesting birds where hot, dry, sunny conditions are the norm, your boxes better provide ventilation so nestlings inside don’t overheat. But here at Salmon Creek, as I’m sure you realize by now, the microclimatic conditions are very different. Winds sweeping off Lake Ontario often subject areas near the lake to temperatures 10-20 degrees colder than places farther inland, not just in Spring but well into Summer. However, boxes at Salmon Creek include features to deal with this. For instance, although box interiors are spacious the door openings are quite small, and include wooden baffles that reduce breeze penetration. And there are no ventilation holes near the roof. For us, less air passage is almost always better.
Our boxes are also intended to be as watertight as possible. Roofs hang well over entrances, and the wind baffles also help exclude rain.
And since the boxes are pretty waterproof they don’t need drain holes in the floor, which, if present, could let in cold air. Plus our boxes face away from the prevailing rain-bearing winds.
So the moral is that it’s not just important to know the requirements of the species one is managing for, it’s equally important to understand how the managment setting, the local habitat and microclimate, impact things, and to take whatever steps are necessary for your species’ success.
For more on nest boxes for Tree Swallows see: http://www.treeswallowprojects.com/buildbox.html.