March 31, 2023
I started monitoring Common Raven nesting during the 2nd Ontario Breeding Birds Atlas (2001-2005). Ravens were uncommon in our region at the time, so I was not expecting to find nests in the squares I was covering. The first nest I found was on a pylon in a power line corridor, the second was on a silo on farm land, the third on the back boom of a tower crane. All were found the same way: I heard a Raven, looked up and saw it fly to a nest on a structure that I would not have checked if I had not heard the Raven.
Year after year, most of the active nests I have found were on silos – 72% of 116 active nests in 2016 and 75% of 124 in 2018, in Eastern Ontario. The silos they use are the concrete staves type, with a dome roof. They build their nest on a small platform at the top of a ladder on the side of the silo, just below the roof; they might also build a nest lower in the ladder or in an opened roof.
In addition to pylons of power line corridors, towers, mini pylons and cross-beams in transformer stations are frequently used. All types of communication towers can host nests as well though the nest is often only partially visible from the ground.
Ospreys also use towers as well as pylons, utility posts and specially-erected platforms. Their nests are similar to those of Ravens and if no bird is present, it might be difficult to determine the species. However, if the nest in on the very top of the structure it is unlikely to be a Raven nest; I have never seen a Raven nest at the very top of such a structure.
Photo: Langis Sirois
Most quarries I visited had a Raven nest. Many quarries have become huge operations with limited or no access. I always seek permission to enter. Ravens also nest on a variety of other structures: railroad and highway bridges; ledges on various types of buildings; and in open buildings such as old barns, stadia, and warehouses.
A pair may have two or three nesting sites in the same vicinity, alternating from one nest to another. They can be different types of structure: e.g., a silo and a barn; a cavity in a quarry or a pylon, tower or silo, etc. Ravens usually don’t tolerate another pair nesting close to their site; the literature says “in a radius of about two kilometres” In fact, I have only seen a few cases of nests closer to each other than two kilometres, the closest I have seen were about 1.3 kilometres from each other.
Ravens are early nesters. I usually start checking possible and known sites in late-February or early-March. Mid-April is the best time to check for young; April 20 is the earliest I have seen fledged young.
Ravens apparently know how to surprise us though: very early breeding was documented by other observers in Ottawa with young in a nest in early February, 2021. The young did not survive a snow storm, but a late nesting in the same general area was probably by the same pair. After a failed attempt, a pair might try again; they either build a new nest or refurbish an existing one.
Checking maps on-line for a specific area is a good way to find possible nesting sites. Sometimes street-view will show a previous year nest on a silo, pylon or tower.
If I am asked why I like to monitor Raven nesting, I am tempted to respond “Because it is easy.” But there is another reason: some human structures on which Ravens nest might not exist in a few decades. I have noted that silos on which they nest are not used much anymore and are sometimes removed, and changes in pylon and tower construction may not be favourable for nesting. I believe it might be useful to document what we observe now, before those changes occur.
Photo: Aaron Hywarren