Reliable trend estimates over large geographic areas are difficult to obtain for many marsh birds (Gerber et al. 2014). Nesting at low densities throughout largely remote areas of western and northern Canada, the western population of Horned Grebe is poorly surveyed during the breeding season (Stedman 2000). Nevertheless, the Breeding Bird Survey (BBS) provides precise, long-term results, and suggests a large decrease in abundance in Canada since 1970, and a contraction of the breeding range toward the northwest (COSEWIC 2009d). All Bird Conservation Regions for which there are reasonably reliable BBS results in Canada are shown below. However, the survey covers only the southern portion of the Horned Grebe's breeding population and the methodology is not ideally suited to marsh birds (Routhier et al. 2014 and references therein). The winter Christmas Bird Count (CBC) provides good coverage of the species' coastal and inland wintering grounds in North America, and the majority of birds counted breed in Canada. However, the species’ preference for wintering offshore or on large water bodies mean that many birds may be missed by CBC surveys from shore (COSEWIC 2009d). CBC results suggest little change in the population since 1970. Considering these sources and relying most heavily on the BBS results because it is more standardized and represents the Canadian breeding population, the Horned Grebe is best assessed as having shown a decrease since 1970, though the magnitude of that decrease is unclear. However, the contrasting results between the BBS and CBC and their limitations means that the reliability of this assessment is considered low. A new approach for monitoring Horned Grebes, based on the Waterfowl Breeding Population and Habitat Survey, could improve knowledge of population status in future (Routhier et al. 2014). The western population of the Horned Grebe, which comprises the bulk of the national population, is currently below the lowest acceptable level relative to the national population goal for this subspecies (see BBS Canada graph below).
The above assessment applies only to the western population. Directed surveys of the small Magdalen Islands population (5-25 adults) show that it has also been declining, by a rate of 2%/year between 1993 and 2007 (COSEWIC 2009d). Though annual nest counts have ceased, staging site surveys have been fairly regularly conducted since 2012 and show a decline. In 2018, only 5 birds (adults and/or young) were observed, and since 2013, a maximum of 9 birds have been observed (adults and/or young; F. Shaffer, ECCC, unpublished data). Although it is possible that some birds may be using an un-surveyed staging area, the high public profile of this subspecies in the birding community and the small size of the Magdalen Islands suggests that this is unlikely. This subspecies has therefore shown a large decrease since 1970. The national goal for the Magdalen Islands population of the Horned Grebe is to increase the population to at least 30 adults (Environment Canada 2013c); it is clearly below acceptable levels of that goal.
Additional information on: British Columbia Coastal Waterbird Survey
Additional information on: Breeding Bird Survey (BBS) - Canadian analysis
Additional information on: Christmas Bird Count (CBC)