I was out walking the other day and observed something strange with one house having a number of pigeons congregating on the roof. (This is not my home, so I have no insight into internal details.) A took a photo, below.
It's a semi-detached home, but the birds were noticeably staying on one side. They wrapped around the home, on both the south and west faces of the roof. The roof has an owl decoy installed, so I gather this must be an ongoing problem.
It's cold out (5C/41F), so I figured the birds just gather around the exhaust vent. But then I'd expect to see them closer to the vent and on both sides of the home.
Then I thought maybe they are catching sun, because it's a south-facing roof. But then I would think this would happen on other houses' roof too.
Is this roof just poorly-insulated? Something else going on?