The northern hawk owl is a medium-sized owl that breeds in the boreal forests of northern North America and Eurasia. They are rare birds across much of their range, which has led to questions about just how scarce they truly are. Some key facts about the northern hawk owl:
- Scientific name: Surnia ulula
- Other common names: northern haw owl, hawk-owl
- Size: 14-17 inches long, wingspan of 28-35 inches
- Identifying features: prominent facial disk, yellow eyes, barred brown/white underside
- Diet: Small mammals like voles, lemmings; sometimes birds
- Habitat: Boreal and mixed forests, muskeg, open meadows
- Range: Northern North America across Canada, Alaska; Northern Eurasia
The northern hawk owl has a widespread but patchy distribution across northern latitudes. Their populations fluctuate dramatically between years, which makes assessing their true rarity complex. Their remote boreal forest habitat and irregular migration habits also make them a difficult species to study. However, available evidence suggests northern hawk owls qualify as a rare species across most of their range.
Population Size and Density
One way to evaluate the rarity of a species is to look at estimates of their total population size and density. For northern hawk owls, these estimates indicate a relatively small overall population:
- Global population size likely less than 300,000 individuals
- Population density ranges from 0.2 to 2.5 birds per square kilometer
- Densities consistently on the lower end across much of range
To put those density figures in perspective, northern hawk owls occur at densities 10 to 100 times lower than widespread owl species like barred owls or great horned owls. Their population densities are more comparable to endangered owls like the spotted owl. Given the vast areas northern hawk owls inhabit, their global population is still sizeable in absolute terms. But their populations are widely dispersed at low densities that qualify them as rare.
Population Fluctuations
Adding complexity, northern hawk owl populations fluctuate dramatically between years in response to prey availability. In peak years, their densities can temporarily increase by 10-fold or more. But these irruptions are followed by steep population crashes once prey is depleted. Their populations go through extreme highs and lows that make it difficult to define a normal baseline for the species. However, the average across these fluctuations still indicates relatively low densities.
Detection Difficulties
Another factor that contributes to the perceived rarity of northern hawk owls is that they are difficult to detect through standard bird surveys. Some key reasons these owls go undetected:
- Remote boreal forest habitat seldom surveyed
- Irruptive migration movements unpredictable
- Roost solitarily in dense conifers during day
- Nest in hidden tree cavities
- Quiet outside of breeding season
Due to these behaviors, northern hawk owls are likely more common than bird survey records would suggest. Their perceived rarity is somewhat inflated by a lack of detectability. However, accounting for detectability still indicates relatively low densities across their range. Efforts to improve detection through methods like broadcast of owl calls have confirmed their fundamentally low numbers.
Range-wide Distribution
Looking across their global distribution also lends insight into the relative rarity of northern hawk owls:
- Sparse and localized across much of North America
- Rare visitor outside of boreal forest regions
- Occurs inconsistently across Eurasian range
- Only common in certain regions when irrupting
While widespread, northern hawk owls occur in low densities and desolate habitats across massive areas of Canada, Alaska, and northern Eurasia. They essentially inhabit the remote hinterlands of the northern latitudes. Outside of irruptions, northern hawk owls are uncommon to rare across nearly all of their breeding and wintering grounds. They reach their highest densities in localized pockets of habitat.
Habitat Specificity
Northern hawk owls are also restricted to specific habitats within their range, especially mature boreal forests. They require habitats with a mix of conifers for nesting and roosting, and openings for foraging on prey. This habitat specificity funnels their already sparse populations into disjunct pockets of suitable habitat. Compared to habitat generalist species, the northern hawk owl’s specialized needs inherently limit their numbers across the broader landscape.
Threats and Protection
Several threats and conservation issues are also relevant to evaluating the rarity of northern hawk owls:
- Boreal forest loss in parts of range
- Climate change impacts on boreal ecosystems
- Rodenticide poisoning on wintering grounds
- Vehicle collisions during irruptions
While northern hawk owls still occupy extensive areas, habitat loss and degradation are concerns for the species’ long-term outlook. No current protections exist for northern hawk owls aside from national park lands. Continued habitat conservation will be important for maintaining viable populations of this rare boreal owl.
Comparison to Other Species
As a point of comparison, northern hawk owls are rarer across their range than related owls including:
- Great gray owls – more localized in distribution
- Great horned owls – much more widespread and abundant
- Snowy owls – cycles more extremely but abundant during peaks
- Barred owls – adaptable habitat generalist
Northern hawk owls occur at lower densities than these other owls across most or all of their respective ranges. They cannot be described as a common owl species by any measure and stand out as rare compared to even closely related species.
Conclusion
In summary, while the northern hawk owl has a extensive global distribution, available evidence suggests they occur in relatively low numbers across much of their range and qualify as a rare species. Their low baseline population densities, extreme population fluctuations, habitat specificity in remote boreal forests, and difficulty of detection all contribute to their rarity. While not endangered, northern hawk owls are appropriately described as uncommon, scarce, and rare across the majority of their breeding and wintering grounds. Conserving extensive areas of mature northern forests will be key to maintaining viable populations of this unique and rarely seen boreal owl.