On Monday, June 30, 2025, an unusual hawk was seen by two seasoned New Brunswick birders. It was perched in a tree near their home at Second North River, NB (near Salisbury). It was on the edge of a newly-cut hay field where it had been feeding. Recognizing it as unusual they checked it more thoroughly including photographing it. An expert confirmed their identification, an adult dark morph Swainson’s Hawk! Other common names for this species are Grasshopper Hawk, Locust Hawk and Harrier Hawk.
The Swainson’s Hawk (Buteo swainsoni) is a western North American species and is very rare here in the east. There have been only a few previous records in NB and they were not well documented with photographs. Most that have been seen here have been immatures. There was a juvenile reported from Waterside on 10 October 2002. I saw the immature found at Shepody Marsh near Hopewell Hill on 5 December, 2011.
In summer this truly western species is fairly common and easily seen in grassland habitats and agricultural areas of the Great Plains westward but not on the Pacific coastal plain. It occurs east to NW Illinois and northward to central Alaska and the Northwest Territories (rarely). It breeds southward through the western US states to north central Mexico.
Migration in this species can be thought of as a mass exodus to and from Argentina. This species is the second longest migrant of any North American raptor. The Arctic nesting Peregrine Falcons fly farther. The migration flight of the Swainson’s Hawk from breeding grounds to the pampas in Brazil or Argentina can reach 11,400 km, taking as long as 2 months. During migration they gain altitude by soaring in circles on a rising thermal. They then set their wings and glide for long distances. They slowly lose altitude and repeat the process when they meet another thermal. This gives the effect of the birds being strung out in groups across the sky.
As the migrating birds make their way to South America they all pass over the Isthmus of Panama. Concentrations over sites such as Panama City, Balboa and Ancon Hill are spectacular. Here they cluster in ‘great towering tornadoes of birds’. This would be a birders dream to see. A similar effect occurs over a narrow corridor in the Andes Mountains.
So, what is an adult Swainson’s Hawk doing in New Brunswick in summer or anytime? Well, the entire population is migratory. Most birds move to southern South America (Argentina) in winter. The counts of migrants over Veracruz, Mexico average over half a million! A number winter in southern Florida, S California and S Texas. Swainson’s Hawks are rare but regular fall and spring visitors to eastern North America. The records show many sight, specimen and banding records from all states and provinces. Being on the edge of the east, one can understand why we see so few. Why this bird is a wandering adult we cannot explain. As one of our birders said, it should be in our prairie provinces looking after its nest or fledglings.
The diet of this hawk is mainly grasshoppers and locusts but also small mammals and rodents. This accounts for its common name, ‘Grasshopper Hawk’. Undoubtedly our visitor was enjoying the grasshoppers in that newly mown field!
The Swainson’s Hawk is a large Buteo. It resembles the shape of other members of its genus; the Red-tailed, the Red-shouldered, the Broad-winged, and the Rough-legged Hawks (along with others not common here). It is 53 cm. long with a wingspan of 132 cm. Compared to the Red-tailed Hawk, it has a shorter body length but longer, narrower wings. The long wings of the Swainson’s Hawk reach or slightly exceed the tail tip on perched adults. This is a good field mark.
The plumages of this species can be described by three morphs or types. These are not definitive, because individuals can vary in a continuum from light to dark and all stages in between. The photos shown above are of the individual which was seen in New Brunswick this past week. That individual is an adult dark morph.
The various plumages of this species are varied and interesting. Let’s look at them here. Our visitor is a lighter version of a DARK MORPH. Dark morphs are rare and comprise only 1 to 10 percent of the population. In some geographical areas they can vary up to 35 % of the local population; e.g., northern California.
In the DARK MORPH the body and upperwing and uppertail coverts are overall dark brown. Most have pale, barred with dark brown undertail coverts. Underwing coverts are dark brown and rufous but can be completely dark brown.
Our visitor appears to have dark brown upper wing coverts and this probably extends over its back and head. The undertail does appear pale and barred with dark brown. The underwing coverts cannot be seen but the light colour showing on the forward edge of the wing suggests there is some light colour on the wing linings. The white face on this bird is typical of the species.
Some other species of buteos have dark morphs (Red-tailed, Rough-legged) so if this bird were completely dark, how could we tell it from these other species? All other dark morphs of other species have dark undertail coverts and silvery flight feathers.
The LIGHT MORPH is the most common plumage. It also has the white face. Its rufous to dark brown breast looks like a bib that contrasts with the light belly. This white belly can be spotted or barred. The underwing is two-toned, with creamy or white coverts over gray flight feathers. The head and underparts are of 3 possible types: 1. head rufous or dark with a gray face, rufous breast, white belly and leg feathers which can be lightly marked with rufous. 2. head dark brown, breast rufous, belly white with dark spotting, leg feathers white. 3. head and breast dark brown. All types have a white forehead and throat.
The RUFOUS MORPH is similar to the light morph but with rufous belly and leg feathers. Males have a gray face and completely rufous underparts. They lack the contrasting darker bib and dark barring. Females have dark brown faces, breasts and dark markings on their rufous bellies The underwing of the rufous morph is two-toned with rufous and creamy coverts over dark flight feathers. Their white undertail coverts contrast with their rufous belly.
Besides these plumages also described are light and dark intermediate plumages. This is obviously an attempt to describe or categorize the continuum in plumages from very light to very dark. The JUVENILE plumages are also variable and best learned by looking at the literature. By late spring some juveniles show sun bleaching on their head feathers, appearing white. Year-old birds are similar to juveniles but have wide subterminal tail bands.
In all plumages one notable feature is the dark trailing edge of the underwing. This distinguishes this species from all but a few other hawks. Here in NB the Osprey and the Northern Harrier would be in that group.
The flight of Swainson’s Hawks is notable. Their wings are long and slim and two-toned underneath. Their tails look long and the bibs on light morphs are visible. Wing positions are also notable. They often fly with the wings in a dihedral position and they will hover over feeding areas in search of food.
What other species do we need to differentiate this species from? Here in NB we could usually rule out Swainson’s Hawk because it is so rare. But now that we have better optics and cameras we have better observation skills than our predecessors. In the west it has to be differentiated from the Short-tailed Hawk and the White-tailed Hawk. We won’t concern ourselves with those species here since they are extremely rare. Here we do have to consider the Red-tailed Hawk. The Red-tailed has shorter, wider wings which it does not hold in a dihedral position. It also has the palatial marks on the leading edge of the underwings and the wings are evenly coloured underneath. You might also be able to see the dark belly band of the Red-tailed. When perched the Swainson’s wing feathers extend beyond the tail tip. This does not occur in the Red-tailed.
The Swainson’s Hawk was first described by Charles Bonaparte in 1838. It was named after William Swainson, a British naturalist. Swainson’s Hawks often live to be 20 years old. The oldest record is 26 years. Causes of death include vehicular collisions, illegal shooting, electrocution, and severe weather. Egg infertility is also a problem in some areas. Overall population decline is attributed to pesticide use on the wintering grounds. Over the breeding range the population is stable. However, in some places especially in its far western breeding grounds it has drastically declined (Oregon, California). Habitat loss is probably a big factor there.
Swainson’s Hawks have interesting forms of feeding. They often soar over a field looking for grasshoppers, dragonflies and other insects. They will show the dihedral wing position or sometimes hover while doing this. They sometimes course low over a field like a Northern Harrier. They will still hunt from a perch and watch for insects which they fly out and grab with their foot and then transfer it to their mouth while flying. They will sit on the ground or walk around and wait for prey. They are attracted to haying, mowing and ploughing so our western farmers must be very familiar with this species. Besides insects they also hunt small mammals and reptiles. They eat a lot of gophers, ground-squirrels and free-tailed bats.
The call of the Swainson’s Hawk is a high thin scream that falls off at the end. It sounds like a weak Red-tailed Hawk’s call.
It is always interesting to find a rare species in NB. It gives a learning opportunity and widens our knowledge of birds and their life histories. Why is this new visitor an adult when all previous records have been of juveniles? We don’t know the answer but all migrating individuals are subject to getting blown off course or misinterpreting their internal navigations. Some do make mistakes. Perhaps that is what happened in this case. Hopefully it will stay around NB until fall migration and it will then go south to meet the huge numbers of its species as they wend their way to cross over to South America.
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