Bird Bath: Some swallows decide not to leave for the winter

story by Bernard Brown | photos by Christian HunoldI’ve been dazzled more times than I can remember by the high-speed acrobatics of hunting swallows—but never in late December.  ¶  Rough-winged swallows aren’t rare in the Delaware Valley. Like most of our insect-eating birds, the swallows thrive in the Northeast during the summer and in the winter, head south where there’s more to eat. However, when a breeding ground is provided for yummy chironomid midges (small flies) during the winter months, the swallows stick around.

Thus a couple weeks before Christmas I stood with environmental educator and birder Tony Croasdale, photographer Christian Hunold, and Philadelphia Water Department science technician Justin O’Brien at the Northeast Wastewater Treatment Plant. Above our head rough-winged swallows zipped through the sky, picking midges out of the air.

The relatively warm contact ponds (where treated wastewater is left to bleach to kill off any lingering microbes) host a breeding population of midges through the winter. Apparently some of the swallows that enjoy them during the summer decided they’d be better off around these ponds than flying the two thousand miles to Central America.

Swallows live life on fast forward. We saw them rest for only seconds at a time before taking off again; a cloud of birds darting and banking a few feet above our heads, they were maddening to follow with sluggish human eyes. The wastewater treatment plant is a work of steel pipes and pumps with water coursing through rectolinear pools. The obvious artificiality made the experience of observing wildlife all the more surreal. 

Contact ponds at the plant host breeding midge populations during the winter.So many of our swallows, though, see no problem in making a habitat from the built environment. Think of barn swallows, which evolved nesting in caves, now make their homes primarily in our buildings. Similarly, other swallows, including the rough-winged, take advantage of walls that simulate their “natural” cliff nesting sites. Moreover, there is nothing new about humans altering wildlife food supplies. For example, birdfeeders have extended the geographic range of cardinals. Maybe in the green space of our backyards it’s easier for us to ignore our influence on our wild neighbors’ behavior, but at the inescapably industrial wastewater treatment plant, our tinkering is impossible to miss.

Birders looking to increase their Christmas bird count totals have been visiting the treatment plant swallows for years, spotting them through the perimeter fence. But, as O’Brien told us, in a post-9/11 world, the Water Department doesn’t like people hanging around the plant with binoculars and high power zoom lenses.

There are plenty of places for birding in Philadelphia, even if you wait until April to watch our swallows fly over our rivers and ponds. On that same visit to the treatment plant we heard more-typical winter birds singing from an adjacent patch of woods: Croasdale picked out Carolina wrens, white-throated sparrows, downy woodpeckers and cardinals. Two red-tailed hawks soared high above us as they scanned the rougher land along Frankford Creek for prey.

We could have stood there mesmerized by the swallows forever, but we felt bad keeping O’Brien away from his work and I had to get back to the office myself. The swallows had no plans to leave.

BERNARD BROWN is an amateur field herper, bureaucrat and founder of the PB&J Campaign (, a movement focused on the benefits of eating lower on the food chain.