The Canadian population of Black-billed Magpie is monitored fairly well by both the Breeding Bird Survey (BBS) and the Christmas Bird Count (CBC). Overall, the BBS likely provides a more reliable signal of population trend, as both sources sample a similar proportion of the population, but the design of the BBS is more standardized. The BBS trend for Canada shows fluctuations on a roughly 10-12 year cycle, with a decline from the early 1970s to mid-1980s, a modest rebound until the early 2000s, and an overall decline ever since, to a level 22% below the early 1970s. The only notable deviations from this pattern are in northwestern Ontario, where there has been a substantial long-term increase, and in central and southern British Columbia and the Rockies, where a decline from the early 1970s to the late 1990s has been offset by an increase ever since. In contrast, the CBC trend shows a fairly steady increase ever since 1970, amounting to a 38% growth in the population over that period. Overall, the population is considered to have undergone little change relative to 1970, but confidence is only medium because of the contrast between the BBS trend that is on the verge of a moderate decrease, versus the CBC trend of a moderate increase.

The goal for Black-billed Magpie is to maintain its population at or above the level it was at in the early 1970s, based on the Breeding Bird Survey. Recent data show that the population is within its goal range.