The dark feathered irruption of Centretown - what's going on?

It seems that this winter many Centretown, Vanier, New Edinburgh residents and possibly more (Overbrook? Hintonburg?) are seeing incredible amounts of crows descending into tree tops at sunset to roost for the night.  It's been an incredibly sight and has really lit up the twitterverse and instagramland with many wondering what is going on.  It may not be a true "irruption" but it definitely is unusual.
irruption (ĭ-rŭp′-sh(ə)n): ecological term for a sudden increase in an animal population (link)
~ Crows starting to gather at Pleasant Park Autumn 2015 ~

Crows roost in flocks every winter for safety and warmth.  They will travel many kilometers away during the day visiting various locations looking for food.  You may notice that there will still be a group of them during the day but not large flocks.  These smaller groups are many times families - as  the "teenaged" crows stick close to parents for up to five years, helping to raise younger siblings.  But these daily family units will always return each winter's night to the communal roost.  

In Ottawa the large roost was in the Alta Vista area for years.  In 2011 there was an editorial about this roost and the efforts to dissuade the crows from staying each night.  The roost included patches of woodlot both north and south of the Ottawa Hospital on Smythe Road (Balena, Coronation, Pleasant Park, Valour) and while some residents were obviously irked, others appreciated their nightly crow neighbours.

~ See the small line of crows going east? Vincent Massey Park 2014 ~

Whenever I was driving north on Riverside around sundown in the cold winter months, I would see a constant stream of black birds flying northeast towards the roost - at first in singles in small numbers but the stream of birds would get busier as it got closer to twilight.  We went to see that roost a couple of years ago in Pleasant Park and it was incredible to see them all settling in for the night.  I also heard recently that they gathered in the Hurdman area by the river.

But this winter they seem to have moved further north.  One of the reasons could be all the construction on Riverside disturbing the roost in Hurdman woods.  Possibly the busier shopping area with lighting at night could have disturbed the ones in Coronation?  I've been meaning to go to their old roosts this winter to see what else could be disturbing them or perhaps it's an over crowding of them - was this a boom year for crows?

I came upon a small group of them this month at the north end of the Aviation Parkway.  They were moving east towards the Rockcliffe redevelopment (Wateridge Village) and north along the river. I've never seen them in those numbers in this area before.  This year is definitely different.  Some may think that it is the ease of sharing information socially which has made it feel like an influx.  But many times the online discussion is starting with: I've never seen anything like this before!  Large groups are being reported along Ogilvie, in Vanier and in Centretown.  What's making them move north?

Every spring these roosts will disperse and disappear as crows choose their own preferred location to raise their young.  This winter "crowdsourcing" phenomenon happens only in the colder, darker months.

Let us know if you've seen them in your area!


Cornell Lab of Ornithology
National Wildlife Federation
Crows Taking Over Ottawa

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