Monday, March 10, 2008

Ruling the roost.

At this time of year Northwestern Crows can be seen nipping small branches off live trees in order to construct their inelegant stick nests. When not doing that, they are either attempting (possibly succeeding) to open your curbside garbage bin, or harassing the few species larger than they are.

Northwestern Crow, trash-talking.

The latter two, obnoxious, activities are carried out year-round, but the nest building signals a major switch in behaviour here, in the Fraser River Delta, for it means an end to the nightly monster crow roosts.

The Northwestern Crow is one species that has thrived as forest and wetland have been converted to farm and city. It does very well in open suburban landscapes, and is able to adapt to human habits and habitation.

Northwestern Crow, trash-taking.

Based on Christmas Bird Count data, from 1957 to 1993, the number of crows in the Vancouver BC area increased from 500 to almost 20,000, and the trend has been upward from there. In several locations, one notably in the City of Burnaby, east of Vancouver, and a second right here in Richmond, from late summer until March, tens of thousands of crows gather in late afternoon, streaming in from all directions, to spend the night in mega-roosts. Our previous house was in a new, still expanding, subdivision that lay along the border of the Richmond roost. Every evening, Hitchcock-like, crows would line the roofs of every house and garage on the street. 26 crows per house-top. It was always 26 crows, because the houses were all the same size, and the crows always perched the same distance apart. One peck-span, I hypothesized.

Northwestern crows on the roof of our garage.

As two by two crows leave the mass roosts to construct nests and raise young, the evenings become quieter and calmer. There are always a lot of crows around, but they’re in a no-nonsense, parental frame of mind, leaving the ravens and raptors alone, except when a pair of Red-tailed Hawks ill-advisably decides to nest anywhere near a territory that feeds the monster roosts.

One red-tail down.

One to go.


April said...

That's a precious picture of a Crow and a Bald Eagle perched in the same tree!

Hugh said...

Thanks. I like how the eagle seems to be straining to remain dignified with the uncouth crow hassling him.

BerryBird said...

Crows flock by the thousands in my city, too. I love that you counted the 26 birds enough times to confirm it was always the same number.

Hugh said...

I discovered the "26-crow principle" by accident, when my son was learning to count.