Description And Identification

The Northern Harrier (Circus hudsonius) belongs to the Accipitridae family. While they are a species of hawk, they are not too common to our west coast side as they would be in other parts of Canada. While uncommon, they are raptors nonetheless, and are built noticeably so. C. hudsonius is neither the largest, nor the smallest, hawk out there but have the flight speed and claw strength on par of many other raptors (AllAboutBirds). These raptors weigh on average anywhere between 300-750 grams, or 10.6oz-26.5oz if you aren’t keen to the metric system (AllAboutBirds).

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They have owl-like faces which help them listen for prey when in flight as well as some sex-specific plumage coloration. Females and juveniles have mostly brown feathers with dark inner secondaries. They also have a ‘pale bar’ along the front edge of the wing and an adult female will have a distinct white patch of feathers on their tails. The males have less variation of plumage colors with the body being mostly gray and an underbelly of white, and a black banded tail. They also have blacked tipped wings, but are easiest identified by their white-rumped tail. Juveniles also have some sexual dimorphism when it comes to their eyes. Male juveniles have green-yellowy eyes while the females have dark brown eyes (AllAboutBirds).

I like to personally think of their flight call as a child who has woken up in the middle of the night from a nightmare screaming “mom! mom! mom!”

Northern Harrier flight call as a male approaches female. Credit to Paul Marvin.

Habitat and Distribution

Northern harriers use a variety of habitats, from marshlands and prairies to the arctic tundra (Paprocki N. et al. 2015, All About Birds 2020). They are commonly found in open areas, as that is where they are at their best when it comes to hunting. In North America, they tend to breed more in Canada than the U.S. but do breed in Alaska. Breeding in Canada happens along the Canadian shield and interior plains, rather than the coasts of B.C., which tend to be more mountainous regions. Non-breeding parts of the year send the northern harrier to the U.S. and upper parts of Mexico and Caribbean.

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Although they spend a fair amount of their time in Canada, once winter roles around, they migrate to warmer places like Mexico and the Caribbean. They tend to avoid snow and can end up in similar habitats as their breeding grounds, flat marshy areas as well as plains. Their prey includes small birds, mammals, amphibians and voles, with a heavy preference to the voles. Vole preference comes from the lack of hiding possibilities, such as with amphibians that can hide underwater, and songbirds that can dart in and out of bushes.

Behaviors and Conservation

Northern Harriers, although are hawks, hunt more like owls. As mentioned prior, they have an owl shaped face disk, which helps direct sound towards their keen ears. These raptors rely more-so on their ears than their eyesight, as they tend to fly lower to the ground listening for prey, rather than spotting it from afar like other hawks. When hunting, they circle around the area multiple times and can appear almost as if they are hovering in place. In the winter they hunt mice and other small mammals as well as smaller bird species (Paprocki N. et al. 2015).

Their nesting locations are usually in boreal forests, but nests can be found in open fields too. These birds stay relatively lower than other flying raptors (Atlas of the Breeding Birds of British Columbia). The males usually are the ones hunting, while the female stays behind at the nest to protect the eggs and offspring(Vukovich and Ritchison 2006). These birds have also been observed to meet in the air and pass off food. The female will usually rise to meet the male who has been hunting, while the male tries to get into position to toss the caught prey to the female to bring back to the nest and feed the young. While this may seem like a bit of a gamble, leaving the nest unguarded for some time, it is a behavior that is practiced by the entire species. Even the juveniles partake in the food toss once they gain their ability to fly, in order to train themselves to hunt as well as get more food for themselves.

According to ICNU’s ‘Red List’ in 2016, the northern harrier is of the least concern when it comes to conservation practices. They were noted to be in decline (IUCN). Declining populations were said to be caused by the use of pesticides and the ever increasing threat of global warming causing habitat loss (BirdWeb). With global warming, it is projected that the northern harrier will lose more habitat in America and will be pushed to the more northern parts of Canada, such as the Yukon and parts of Nunavut and Alaska.

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Fun Facts

Northern Harrier’s have earned the nickname “grey ghosts” due to the male’s fast, yet silent hunting speed and plumage coloration. The name also fits the northern harrier based off of it ability to seemingly hover in place like a ghost watching from a distance.

Taxonomists split the northern harrier (Circus hudsonius) off from the hen harriers (Circus cyaneus) based on differences found in a genetic analysis. They also based this split off on locations where they found hudsonius and cyaneus. For example, the northern harrier is found mostly in North America, while the hen harrier is found mostly in parts of Eurasia. The two species are visually similar (Oatley et al. 2015).

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The northern harrier has the identification 4 letter code of NOHA, meaning that should you ever get to band one or meet one, you should definitely name it ‘Noah”.

Research

Northern harriers have been used to measure mercury contamination in the environment. Because they are carnivores that prey on small songbirds, they ingest whatever the prey ingested previously. This can lead to a process called biomagnification, where the toxin, like a pesticide, is found in successively higher levels of a food chain. The songbirds prey on insects that have become contaminated with mercury which then contaminates the songbirds, who gain a larger concentration of the mercury. When the northern harrier eats the songbird, they too become contaminated with a higher concentration of mercury. By measuring the amount of methylated mercury (MeHg) found in northern harrier feathers, the level of contamination in an environment can be approximated. It was found that raptors that feed on songbirds that are insectivores, rather than the songbirds that prey on seeds and grains, were more likely to have a higher concentration of mercury in their blood. This was particularly prevalent in males, as they are the ones who do the hunting most of the time. (Bourbour et al. 2019)

Northern harriers have also been found to have a 4 year migration cycle, that revolves around hunting specific voles. While this was true for interior regions, those that were found to live on the Atlantic were not found to follow a 4 year time gap. As one area runs low on prey such as these voles, the northern harrier will migrate elsewhere and hunt there instead. This may be to give the voles a chance to recuperate their population so that the harriers can continue hunting at a steady but not overbearing pace. It was found that the cycle at which the a northern harrier takes to return to the same general area is roughly 4 years (Schimpf et al. 2020).

Closing thoughts

Northern harriers (Circus hudsonius) are raptors that are of least concern when it comes to conservation practices. They are sexually dimorphic, with females and juveniles having brown plumage and an easily recognizable white rump, while the males are grey with a white underside. They notably hunt different from other raptors and stay low to the ground, hovering and listening for prey, which is further aided by their owl like face disks. The northern harrier is found mainly in Canada and the U.S., but also in Mexico and parts of the Caribbean. They like to stay close to marshlands and plains and open fields to fully optimize their hunting abilities. Finally they have recently been split apart from hen harriers (Circus cyaneus) by taxonomists due to genetic and geographical differences.

References

All About Birds, https://www.allaboutbirds.org/guide/Northern_Harrier/id (accessed Oct. 12, 2020)

Audubon, https://www.audubon.org/field-guide/bird/northern-harrier (accessed Oct. 12, 2020)

Ebird, https://ebird.org/species/norhar2 (accessed Oct. 12, 2020)

IUCN Red List, https://www.iucnredlist.org/species/22727740/94959659 (Accessed Oct. 12, 2020 and Nov. 17, 2020)

BirdWeb, http://www.birdweb.org/birdweb/bird/northern_harrier (Accessed Nov 17, 2020)

Paprocki, N.; Glenn, N.F.; Atkinson, E.C.; Strickler, K.M.; Watson, C.; Heath, J. Changing Habitat Use Associated with Distributional Shifts of Wintering Raptors. J Wildlife Manage 2015, 79, 402-12. DOI

Bourbour, R.P.; Martinico, B.L.; Ackerman, J.T.; Herzog, M.P.; Hull, A.C.; Fish, A.M.; Hull, J.M. Feather mercury concentrations in North American raptors sampled at migration monitoring stations. Ecotoxicology 2019, 28, 379-91. DOI

Youtube. Pacificnorthwestkate. Northern harrier hunting the marshlands May 13 2019, https://www.youtube.com/watch?v=jxdrmgnMA0g, (Accessed Oct 19, 2020).

Oatley, G.; Simmons, R.E.; Fuchs, J. A molecular phylogeny of the harriers (Circus, Accipitridae) indicate the role of long distance dispersal and migration in diversification. Mol Phylogenet Evol 2015, 85, 150-60. DOI

Schimpf, D.J.; Goodrich, L.J.; Kocek, A.R.; La Puma, D.A. Northern Harriers Have A geographically Broad Four Year Migration Cycle. J. Raptor Res. 2020, 54, 38–46. DOI

Vukovich, M.; Ritchison, G. Nesting Success and Behavior of Northern Harriers On A Reclaimed Surface Mine Grassland In Kentucky. J. Raptor Res. 2006, 40, 210–16. DOI