Population status

Ferruginous Hawk
(Buteo regalis)

There are three main sources of population change information for the Ferruginous Hawk in Canada. Both the Breeding Bird Survey (BBS) and the Christmas Bird Count (CBC) provide long-term population data at national and continental scales. However, neither survey design is ideal because Ferruginous Hawk home ranges are large, their population density is low and prone to fluctuations related to changes in prey availability, and neither survey provides complete coverage of the species' range. Results from the CBC are further complicated by the fact that the proportion of Canadian birds relative to the larger American population is unclear. Nevertheless, the BBS covers more than half of the breeding population, data go back to 1970, and the trends are precise; results suggest that the population has increased by more than 50% in Canada relative to 1970. Results from the CBC also show a moderate increase (~40%) in the continental population, which are mirrored by continental BBS results (see below). The third source of information comes from a targeted, nest-based survey in Alberta, the core of the species’ breeding range in Canada. The Ferruginous Hawk's breeding population has been estimated every five years, beginning in 1982. This survey suggests a decrease in the number of breeding pairs (categorized as a moderate decrease but bordering on little change); the population peaked in 1992, then declined sharply back to levels found in the early 1980s (Redman 2016). This presents a slightly different picture than results from the BBS and CBC, but this survey only provides information for a part of the species' range and has a shorter timeframe. Considering all three sources of information together, the species can perhaps be best assessed as showing a moderate increase relative to 1970, but with low reliability due to the disagreement between the national/continental results and the regional results. Because there is uncertainty in this assessment, a quantitative goal based on the primary survey (the BBS) has not been set, however because the species is listed under the Species At Risk Act (SARA), it is clear that the Ferruginous Hawk population is below the lowest acceptable level. Once the Recovery Strategy is developed under the SARA, the national population goal will be re-examined.

 

Population goal and acceptable levels of variation

Species/groupGoalLower levelUpper level
Ferruginous HawkAbundance required for de-listing (SARA)Equal to goalNot applicable

Breeding Bird Survey (BBS) - Canadian analysis

Additional information on: Breeding Bird Survey (BBS) - Canadian analysis

Table 1: Population trends by geographic area
Geographic areaTime Period Table 1 - footnote 1 Annual trend Table 1 - footnote 2 Limits
LowerUpper
Canada Select to view graph of the geographic area: Canada 1970-2016; Breeding Bird Survey (BBS) - Canadian analysis1970-20160.9-0.52.2
Canada Select to view graph of the geographic area: Canada 2006-2016; Breeding Bird Survey (BBS) - Canadian analysis2006-20161-2.34.4
Prairie Potholes Select to view graph of the geographic area: Prairie Potholes 1970-2016; Breeding Bird Survey (BBS) - Canadian analysis1970-20160.9-0.52.2
North America Select to view graph of the geographic area: North America 1970-2016; Breeding Bird Survey (BBS) - Canadian analysis1970-20160.90.31.4
 

Picture of logo Christmas Bird Count (CBC)

Additional information on: Christmas Bird Count (CBC)

Table 2: Population trends by geographic area
Geographic areaTime PeriodAnnual Trend Table 2 - footnote 1 Limits
LowerUpper
North America Select to view graph of the geographic area: North America 1970-2016; Christmas Bird Count (CBC)1970-20160.7-0.31.5
 

Alberta Ferruginous Hawk Inventory

Table 3: Population trends by geographic area
Geographic areaTime PeriodAnnual Trend Table 3 - footnote 1 Limits
LowerUpper
Alberta Select to view graph of the geographic area: Alberta 1982-2015
; Alberta Ferruginous Hawk Inventory
1982-2015
   
 

References