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Nesting Season is Upon Us

Spring migration ended in early June, and that brings us to the heart of nesting season. All of the birds typically seen across Southwestern Ontario in June are nesting for at least part of the month. For most of these birds, the breeding season extends through to mid-July.

That said, there is some nesting that occurs all year. It surprises some to learn that Rock Pigeons breed here year-round. That says a lot about how this species has adapted to urban life and also about how hearty these birds are. They wouldn’t do this if they didn’t have success. Another bird that breeds here through all or most of the year is the Eastern Screech-Owl.

The Great Horned Owl’s nesting season is early and long, running through the winter and well into June. Mourning Doves are known to have an extended breeding season that runs from mid-March through to later September. A pair of Mourning Doves will have up to six broods per year. There are several species that start nesting in the early spring. Mute Swans typically nest from April to August, and Northern Cardinals from mid-April to mid-August.

But many of our songbirds nest between late May and mid-July. The Yellow Warbler’s nesting dates fit this range perfectly. The Red-eyed Vireo’s nesting dated are typically May 31 to July 31.

Not surprisingly, Brown-headed Cowbirds, which are parasitic nesters, take advantage of this window when most other songbirds are on the nest. This is when female Cowbirds will stealthily lay eggs in the nests of other birds.

There are a few birds whose nesting dates skew a little later. The American Goldfinch, for example, typically nests between June 12 and July 31. The “shoulder season” for their nesting can even stretch into September. This is largely because the Goldfinch diet is exclusively seed-based. One of their preferred seeds is thistle and the plant doesn’t go to seed until we are well into the summer. So that the Goldfinches can ensure a steady food source for their chicks, their nesting is somewhat later than many other birds.

If you watch any of the London-area birds closely, you may well see breeding bird behaviors. You might even be led to a bird’s nest site. It is fascinating to observe birds on and around a nest. At the same time, bear in mind that the welfare of the birds should always trump our curiosity about them.

Local birders have followed with interest a pair of apparently nesting Black-necked Stilts at the Strathroy lagoons in west Middlesex. This would represent a shift for the species.

Bird scientists track and study bird populations closely and pay particular attention to species distribution, abundance, and where birds reproduce. Data for these studies are crowd-sourced, with citizen scientists gathering data in the field through initiatives such as the Ontario Breeding Bird Atlas. Atlassing of breeding birds has given rise to its own language that includes “safe dates” – dates during which it can be safely assumed that a particular bird species is nesting – and breeding codes such as “visiting probable nest site” and “adult carrying food for young.”

If you missed the informative article about atlassing that Laure Wilson Neish created for Bird Friendly London, check out Invitation To Observe - Ontario's Breeding Bird Atlas.

Red-eyed Vireos are currently nesting in the London area. They are typically on the nest between May 31 and July 31. Photo by PAUL NICHOLSON

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