The Irruption of Swainson’s Hawks on the Regina Plains

Weyburn, Saskatchewan, has a population of 8,000 people and services wheat growers, stockmen, and roughnecks drilling for medium oil. We observed scores of hawks in the ditches, on power poles, in trees, and along the train lines as we left Weyburn for Regina, 70 miles distant, one June morning. Along the journey, we counted 113 hawks.

Most of them had white heads, like Rough-legged Hawks. However, it seems that Rough-legged Hawks are still present in southern Saskatchewan. In the spring, Rough-legged Hawks travel through Saskatchewan on their way north to the Arctic, where they spend the summer. In the autumn, they pass through Saskatchewan. The birds we saw had white spots on brown mantles, comparable to Rough-legged and Red-tailed Hawks, as well as the plumage of Red-tailed Hawks. These birds’ white feathering did not follow the symmetrical zigzag pattern seen on Red-tailed backs. The Red-tailed Hawk’s light orangy-red tail was also not visible. Some had a belly band, which further to the confusion with both Rough-legged and Red-tailed plumages. A few of these birds had all-white bellies, which might imply that they were Ferruginous Hawks. However, the royal Ferruginous’ puffed-out chest and flat crown were not visible. This bird was smaller, with slumped shoulders and a tiny round head. It was without a doubt a Swainson’s.

The year of hatching Swainson’s Hawk has tawny and brown underparts with dark brown striping. This buteo may appear considerably different from either juvenile or adult plumage in subsequent years, until complete adult plumage. It is distinguished by a whitish head, varied white plumage on the underparts, and white splotching on the light brown upperparts. Some of these traits are shared by both young Ferruginous and Red-tails. We now had a fantastic chance to learn to make these differences. We were seeing one of birding’s most unusual happenings.

Between the hatching and mating seasons, bachelor groups of Swainson’s Hawks congregate, feasting where there is abundant of food and then moving on when feeding possibilities diminish. We were going to be able to analyse plumage changes in stationary birds in a specific region. Our initial objective would be to identify the location and the quantity of birds there.

Large hawk counts are often conducted during migratory seasons and at well-known locales throughout North America. Summer observations are often confined to watching pairs of territorial hawks. Bands of non-breeding Swainson’s Hawks are reported to spend the summer together at the border between Saskatchewan and the United States. In this instance, however, the hawks were in a far more accessible location—the Regina Plains, which had a well-developed road system for human convenience.

On our journey back to Regina from Weyburn on June 21, we counted 131 immature Swainsons in ditches, on power wires across both roads, and on the railway rails that run along to Highway 39. Ten immatures were counted on the way back from Regina to Francis the following day on Highway 33, which put us within twenty miles of where we first saw the hawks. We observed twelve non-breeding Swainsons on Highway 35 from Francis to Weyburn, which brought us even closer to the initial observations. There were no immature birds found south of Weyburn.

On the way to Regina from Weyburn on June 26, further comprehensive notes of where the Swainsons were observed were taken: Five birds were observed between McTaggart (five miles outside of Weyburn) and Yellow Grass (another eight miles), and from Yellow Grass to Lang 12, Lang to Milestone 7, with probably more birds if a grain train had not frightened the birds off their tracks. We observed 24 birds between Milestone (halfway to Regina) and 15 miles south of Regina, where the highway joins a wetland. We spotted ten people between there and Regina. One immature bird was sighted from Regina to a location 20 kilometres north. No immature Swainson’s Hawks were discovered on the trip back to Weyburn via Francis.

A pattern was beginning to emerge. The Swainson’s Hawk is a plains bird, so we were not surprised to find none north of Regina or thirty miles east of Regina, where the parkland starts. However, spotting no young birds south of Weyburn on the broad plains was a letdown.

According to some observers, the Richardson’s Ground Squirrel, an open prairie animal (the gopher to most of us), is in decline. They are usually a prominent prey species for the Swainson. Fortunately, a large vole infestation had been seen on the Regina Plains. For the same reason, the young birds were not eating gophers (of which there were few) or grasshoppers. They were gorged on voles.

At this point in our journey, the greatest concentration of young birds has been spotted in constructed habitats: the huge ditches running along to Highway 39 and the Canadian Pacific Railway ditch next to the Highway Department ditches.

On June 28, we chose to go from Weyburn to Regina using agricultural access roads and trails that ran parallel to the two highways we had been travelling to get there. We should never go more than six miles from where we first saw the birds.

Our efforts were not in vain. Six birds were shortly seen near highway ditches. We saw three additional birds as we drove north on rural roads. Two more in an abandoned farmyard beside a path. Two more are following a tractor. Finally, thirty-seven birds were either flying overhead or on the field below, barely two miles from Milestone and Highway 39.

We went straight north at Milestone, parallel to Highway 6. A Kochia slough was being farmed along the route, but no hawks accompanied this tractor. Understorey vegetation such as Kochia weed does not offer food or shelter for rats.

The arrival of the plough permanently altered the land. The disturbed soil not only produced the crops that were imported, but it also allowed for the unintentional introduction of non-native seeds, which are referred to as weeds since they have no economic value. Nonetheless, they offer food for rats. It is uncertain if this has had an impact on rodent numbers and, as a result, hawk populations.

We were able to investigate the region west of the major concentration of birds by taking an alternative route back to Weyburn. We found another side road running south from Regina parallel to Highway 6 and five or six kilometres west. We quickly saw 13 hawks following a tractor ploughing a slough. As we drove south, we saw many small groups of young birds on newly planted stubble fields. There were two in one group, four, eight, and twenty-one in others. Only three hawks were discovered on grazing area along the Missouri Coteau.

Twenty-four hawks foraged on freshly farmed stubble a mile west of Yellow Grass. In other stubble fields, two groups of two were seen. Another in an abandoned farmyard. The total for the day was 156 juvenile Swainson’s Hawks.

Hawks visited stubble fields due of the feed available to prey species, voles, and mice. Stubble is the standing straw that remains after a grain crop has been harvested. It offers refuge for rats as well as food in the form of falling grain seeds.

On July 3, 215 immature Swainson’s were counted while travelling between Weyburn and Regina. There were almost a hundred birds from Milestone to Regina. The majority were on or near areas that had just been cultivated. On the same day, just one immature bird was seen between Weyburn and Milestone, a distance of 35 miles. We collected 460 immature Swainson’s on July 5, our greatest day total in the same region.

Immature Swainson’s Hawks were concentrated in a 70-mile-long by eight-mile-wide stretch of territory between Weyburn and Regina. The ditches, electrical lines, and railway tracks that ran northwest along Highway 39, then straight north to Regina on Highway 6, formed the backbone of this region. Birds may be spotted up to two miles west of the motorways and six miles east of them. There were no birds seen south of Weyburn or north of Regina.

The major concentration of juvenile Swainson’s was discovered in an area of roughly 400,000 acres of cropland and right-of-way ditches. There were probably two to three thousand juvenile hawks around at any one moment. Swainson’s Hawks made up more than 95% of them, with Red-tailed Hawks and a few Ferruginous Hawks rounding out the remainder. Swainson’s were the only ones counted.

In this location, the prevalent winds were west or northwest. More hawks were sighted downwind and at a greater distance downwind than upwind. Upwind hawks were seldom more than three miles from the greatest feeding areas. Hawks may be seen up to 10 kilometres away.

Following that, weekly counts were conducted from Weyburn to Regina. As the summer progressed, the number of hawks sighted weekly decreased. Immature birds, on the other hand, started to be observed outside of the primary concentration of birds. Perhaps they had depleted their early food supply and needed to go farther away to keep healthy. By the end of August, just two immature birds may have been seen along the path where hundreds had been observed in a single day. They had departed as suddenly as they had come on June 1st.

The Swainson’s Hawk is an open plains bird that now nests on trees erected by the farming community. It has adapted well to contemporary technology, preferring to sit on steel railway lines and perch on electricity poles. However, because to competition with the Red-tail, a bigger buteo, it does not hunt among the trees of the parks near to the open plains. The farther east you travelled from the main viewing line, the fewer Swainson’s you were likely to observe. You were about to enter the Parkland ecological zone. There is no simple reason for why no immatures were seen northwest of Regina (open plains till just outside of Saskatoon).

South of Weyburn, you’ll find yourself in short grass grasslands, a natural zone that reaches all the way down to Texas. Swainson’s environment is ideal. However, no immatures were seen south of Weyburn. There was an explanation in this situation. Rains had been few, resulting in a little seed crop for mice and voles to feed on, as well as fewer grasshoppers and Richardson’s Ground Squirrels—all of which provided meal for hungry hawks spending the summer in Saskatchewan.

Many witnesses said that there had been a population increase of voles. The Short-eared Owl was the first to benefit from these perfect vole circumstances. The numerous kinds of hawks that summered in Saskatchewan had now arrived at this dining table.

We spotted more juvenile birds with scruffy whiteheads at the start of our observations. Then we began noticing more birds with missing belly bands. We were seeing distinct white-chested birds and the rare one with a faint orange bib at the end of the summer. Similarly, the birds’ backs lost their white feathers and their brown plumage darkened.

We have joined several nest trees as bird banders throughout the years. Only a mother would cherish a freshly born Swainson’s while it is still alive. When it dies, it becomes food for its nestmates.

The fledgling bird develops tawny and brown plumage while still in the nest. Upperparts have a dark brown colour. Tawny—an orangy brown with varied splotches and streaks in dark brown—are the underparts.

Birds in their second year showed varying degrees of spotting and streaking beneath on a light buff or white ground colour. They exhibited dark brown belly bands, which might be vestiges of their striped juvenile plumage. The heads seemed white, gently streaked with pale browns, but the striping was not visible until up close. The throat and upper breast were also white. Upperparts were creamy brown with many irregular white spots.

Birds in their third summer started to resemble adults. Initially, they were all white below, with no belly band. Upperparts were darkening and losing most of their white splotching. Where the adult plumage will eventually display the unmistakable Swainson’s bib, the heads and upper breasts started to shift from pure white to a light chestnut or even extremely pale tan or yellowish. These birds seemed as a “ghost” of adult plumage at times, a faint wash over what would grow into the deeper delineations of the adult. By the end of the summer, several birds resembled adults, although a little paler all over.

The colour phase that the birds would eventually become complicated all of the plumage differences. Very light birds may be quite pale all around. Dark phase birds would exhibit matching blackness to the confusion of immature plumage.

On the underparts of one immature dark phase bird, the ground colour was extremely dark tan fading into brown, with practically black striping and a black belly band. The tint was virtually black above, but with jagged flecks of lighter brown. The overall impression was of a black, scruffy bird that required thorough examination to determine species. In this situation, the following characteristics were necessary to distinguish the common prairie buteos: posture, head form, bill size, and body mass.

To add to the confusion, any description of plumage will be impacted by the observer’s colour perception, time of day, lighting circumstances, and cultural colour perception. Our goldfish, for example, is called “Poisson rouge” (French for “redfish”). We can anticipate regional variances in colour identification within English-speaking North America.

We had one more adventure to look forward to: going along the Saskatchewan-U.S. border in search of a gathering of both adult and young birds moving back down to Argentina at the end of the Canadian summer. It was thrilling to observe birds rise in a kettle to catch favourable breezes before flying south on their semi-annual migration.

Martin Bailey writes a weekly nature column for the Weyburn, SK newspaper. He has been involved in birding, banding birds of prey, and censusing endangered species for many years. He can be reached at [email protected].

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