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Cliff Swallows At Harris Water Treatment Plant in Toronto

But for a fellow birdwatcher posting a photo to Facebook of the Cliff Swallows (Petrochelidon pyrrhonota) nesting at the Harris Water Treatment Plant in Toronto, neither Bob nor I would ever have known such a colony existed. It was the structural intricacy of their nests that had us making a beeline to The Beach for a look.

The R.C. Harris Water Treatment Plant is a magnificent example of art deco style architecture, and on rare occasions, it is possible to tour the interior to appreciate the stunning domed ceilings, stylized frescoes, arching windows and opulent rotunda.

Perched at the edge of Lake Ontario, the building’s sprawling facade makes a perfect location for Cliff Swallows to set up shop because there is an ample supply of gnats and midges hovering near the shore for the birds to catch and eat. You can see a few of the swallows’ mud structures above the windows tucked under the lips of the crowned panels.

Cliff Swallows are highly colonial, sometimes grouping in hundreds and on rare occasions in thousands, but more typically in smaller numbers. In total, we counted about 25 gourd-shaped nests with each nest supporting a pair of swallows.

There was constant activity around the nests with pairs alternating positions so that each one had a turn within. There also seemed to be a bit of competition for the cavities by House Sparrows.

The sun reflecting off the pale exterior of the building was brilliant that day, yet the air temperature had us requiring jackets and head coverings. Despite a brisk onshore breeze, our clothing was peppered with tiny flying gnats that also insinuated themselves into our hair, eyes and mouths. Yuck!

We found it interesting that the Swallows’ brisk activity around the nests would continue for sustained periods of time, and then suddenly, as though one, the whole lot of them would vacate the nests and soar on high in search of insects.

We later learned that this is typical behaviour for Cliff Swallows, which are sociable birds that assemble in large groups even when they are preening, perching or taking a bath. The flock of Cliff Swallows swooped and dipped like some fine-tuned and choreographed aerobatic airshow, and then just as unexpectedly, the flock returned to their nests and resumed construction…

or settled on the ledge above the nests to rest and preen themselves. Cliff Swallows have relatively short tails that are almost square or very slightly forked. The pale buff forehead may be all that is seen when one of the birds peers out from the depths of its nesting cavity. When in full sunlight, the dark glossy blue of the crown and back is obvious, but in dim light, the head may appear a dull brown like the wings and tail. This photo shows perfectly the pale, pumpkin-coloured rumps that are characteristic of Cliff Swallows.

As one Cliff Swallow returned to the nest, two others eagerly looked on making it possible to see the rich, chestnut-coloured face and small black patch at the lower throat of the one bird. There was no way to tell into which nest the newcomer would enter, and at times, we felt that the cavities must be quite crowded.

Cliff Swallows make their nests out of pellets of mud gathered by the birds giving one reason that these birds must locate their colonies near water. Any source will do no matter how small, ponds or puddles, ditches or lakes, with the birds traveling up to a half mile to get the mud. Cliff Swallows begin by choosing a location that is more or less roofed, in this case by the ledge on the face of the building, or on the face of a cliff with an overhang.

Bob and I were able to discern the gobs of mud in the Swallows’ beaks when they would turn around within the nest and begin to apply it to the edge of the entranceway. Slowly, bit by bit, each pair of Swallows worked to enclose the cavity leaving only a narrow neck for access.

In this case, the Swallow was adding wet mud while outside of the nest using its tail for leverage. The nest on the right is almost complete with the desired size of opening.

It is unbelievable how skilled at construction the Cliff Swallows are. Using a combination of mud and saliva, they are able to plaster their nests to the vertical walls of cliffs, canyons and man-made structures by methodically placing small amounts at a time…

into organized rows. Both the males and females work to construct the nest, and they must work slowly so the mud has time to dry and harden. From beginning to end, the construction of a nesting cavity can take between one and two weeks and consist of between 1,000 to 1,400 mud pellets, which represents as many trips to and from the nest.

If a nest does not have adequate time to harden, or if extremely humid weather persists, a Cliff Swallow’s nest can crumble and fall. In this cluster of mud nests, we can see that one has become occupied by a House Sparrow. This has been the practice ever since House Sparrows were introduced, and it can lead to Cliff Swallows abandoning their colony.

A little further along the ledge, we see another nest that has been usurped by a House Sparrow. This behaviour has been devastating to Cliff Swallow populations.

At the bottom of this photo is a Cliff Swallow just beginning to build a nest house where a brick projects from the building’s wall; a House Sparrow looks on from above. The mud houses are globular shaped with a more or less downward protruding neck forming the entrance although not all nests have this short entrance tunnel. The nests are built close together forming a dense cluster that begins at the highest point possible.

Such was the flurry of activity that these two swallows had a near miss when approaching one nest. Cliff Swallows return to South America for the winter months, then set off on their northward migration in late winter and early spring. Because these birds have a homing tendency, those from a colony will often return to their old nests, which often are durable enough to have survived our harsh winter weather. Even if the nests are in sad shape, they are quickly claimed, occupied and repaired.

Bob and I could have stood there all day watching the Swallows build their nests. They are certainly industrious and meticulous, and in my book, can be compared equally to ants or beavers when it comes to a work ethic. The bulbous nests fashioned from masses of teardrop-shaped blobs of mud are aesthetically pleasing and exemplify the masterful construction carried out by the swallows. They held a certain charm all huddled there in a group in the shelter of the massive water treatment plant, and to think that these birds have been building nests there for years and we never knew. What an awesome discovery!

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