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.
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.