The Canadian population of Great Horned Owl has been monitored over the long-term by both the Breeding Bird Survey (BBS) and the Christmas Bird Count (CBC). The BBS samples much of the Canadian breeding range except in the north, but is not well-suited for detecting owls, although precision of estimates is high. The CBC largely samples the same population, but can include more focused effort on owl detection, and is likely to overall be more reliable for this species. Both sources show a declining trend, but while the BBS indicates an increase until the mid-1980s and a subsequent decline amounting to a cumulative loss of 27%, the CBC shows a steady decline since 1970, with just over half of the population during this period. The BBS is useful in highlighting some of the regional differences in trends, with increases only in south-central British Columbia and the Prairies, and the steepest declines in southern Ontario and Quebec. The Nocturnal Owl Survey is better suited to detecting Great Horned Owl than either the BBS or CBC, but only dates back to 2008. It shows a national decline of 18% over its first 14 years, largely consistent with the BBS and CBC, but has low precision.

The goal for Great Horned Owl is to increase the population to the level it was at in the early 1970s, based on the Christmas Bird Count. Trend data show that Great Horned Owl is currently below its goal range, but it has stabilized its trend over the past decade. Analysis of recent trends and potential growth rates suggests that Great Horned Owl could reach its population goal by 2050 with the support of conservation action.