The “crack of dawn” is way too late for wildlife biologist Andy Stewart to get out of bed. He must be in location thirty minutes before sunrise listening for the calls of breeding Cooper’s hawks. Stewart is trying to band every Cooper’s hawk chick in Greater Victoria and the Saanich Peninsula. To do that, he must first find their nests, which are typically hidden in fir trees 70 feet (21 metres) above the ground.
Stewart has pioneered the “most productive and reliable” way to locate nests. “You don’t see hawks, you hear them. You don’t look, you listen,” he explains. Breeding birds vocalize for a few minutes at first light. Then they stop.
“It is a great technique but I can only hit one site per morning,” Stewart says. He tried using volunteers to listen at other locations. Getting up before 4 a.m. quickly eliminated all but one, his wife Irene.
From mid-February to mid-May, Andy drops Irene off alone in one dark pre-dawn location, while he covers another area. Her help is crucial: it doubles the results of the dawn vocalization surveys. Irene--surely a candidate for “most supportive spouse in Canada”--says the hawk study is a “family project.”
The Cooper’s hawk (Accipiter cooperii) is the region’s most abundant year-round bird of prey. The unbanded adult Cooper's hawk in this photo has the red eye, black cap and slate grey back typical of males. These fast, secretive hawks are crow-size with powerful wings and very long tails. Those long tails--easily seen in flight and when the bird is perched--enable them to outmaneuver prey doing their utmost to escape. They eat small and medium-size birds, especially robins, sparrows, starlings, pigeons, and the occasional rat, all species which thrive in urban environments. They kill prey using their talons, pluck the feathers, then usually eat the head first, followed by entrails and muscle. Hawk stomachs digest bones but they must cough up feathers in small pellets. (Photo by Andy Stewart)
In fourteen years (1995-2008), Stewart has banded over 1,400 Cooper’s hawks. Banding is an essential tool in his on-going study of the breeding ecology of urban-nesting Cooper’s hawks in Greater Victoria and the Saanich Peninsula. Most hawks seen in the region are wearing Andy’s special anodized aluminum colour bands on their left legs. Females wear red bands and males wear black bands. Each band is uniquely coded with two vertical “alpha-numeric characters” (a combination of letters and numbers). The code is repeated three times around the band so it can be read from all angles. The colour-band shown in this drawing would be recorded as "Red B over 6."
Band codes can be read up to 20 metres away with binoculars. With a spotting scope like Andy’s, they can be read up to 75 metres. (Above photo of Andy with scope is by R.W. Campbell) The birds wear a standard aluminum U.S. Fish and Wildlife band on their right legs as well, but these can only be read when the bird is in hand.
Nest area locations in the huge 89 km. study area are indicated by circles on the map below . “Larger lots with trees are where they are nesting,” Stewart explains, "There is a correlation between nests and treed areas, wooded areas,” including public parks, golf courses, larger private properties, Ross Bay Cemetery and University of Victoria. “Hawks don’t nest in tiny yards...Several long term nest areas have been lost during the course of this study to subdivisions and urban in-filling developments." (Map by Andy Stewart)
For the first three years, the hawk study was an official project of the B. C. government and part of Stewart’s paid job as a wildlife biologist. When that project ended, Stewart decided to continue the ground-breaking study on his own time. After persevering for a further eleven years, he says, “I guess you could now call it a serious hobby.” He asks area residents to help by reporting sightings of banded hawks and nest locations (see contact information below).
The ideal age to band chicks is when they are two weeks old, unable to stand and completely docile. The four newly banded fluffy white chicks in this photo remained exactly where they were placed like a row of beanbags. The unhatched egg in front is from the same nest. (Andy Stewart photo)
A skilled climber is needed to reach the nest, place the chicks carefully in a bag and lower them on a rope to the ground so Andy can get to work. He weighs them, measures upper leg diameter and length (left photo below) and upper beak length. Volunteers help by recording data (centre photo). At last, Andy carefully attaches a band to each leg in the photo on the right. (Photos by Norm Ringuette) The height of the nest is measured by attaching a tape onto the bag as it is pulled back up to replace the banded nestlings.
In spring, hawk calls--a distinctive kek-kek-kek--often alert observers to a nest-site. Both male and female hawks carry sticks to the nest. Normally, five eggs are laid in nests lined with bark flakes. When incubating starts, hawks “go completely silent” until chicks emerge and feeding action begins.
Females, much larger than males, stand guard near the nest day after day while males do nearly all of the hunting for the family. Five chicks are common and providing enough food is an exhausting job. Stewart compared the weight of one male hunting for five chicks with his weight the next year hunting for only three. The male was noticeably thinner with a higher workload.
Males visit the nest area briefly to deliver prey. The females receive the food and rip it up for young chicks. Later, as chicks mature, they venture out of the nest onto close branches, and, finally, fly awkwardly to nearby trees.
Stewart has found some hawks change mates every year, but “It is normal if both survive and the previous nest was successful, to re-mate, though it could be in another location.” The all-time mating record for one pair was eight years in a row.
Based on the large number of eggs in nests and the consistently high rate of fledgling success, Stewart concludes hawks “have no difficulty finding prey in this city environment.” Backyard bird feeders concentrate small birds, providing a handy buffet for hawks. 80% of the banded hawks reported by the public were in yards, with more than half at or on bird feeders.
Males seem to remain in the study area year-round, but females are rarely observed during the winter months and rarely near feeders. A few hawks fly far from their original nests: bands have been recovered from Nanaimo, Delta and Boundary Bay in B.C. and as far away as Washington, Nevada and southern California.
Though Stewart has tracked one male for nine years and three others for eight, banded hawks usually disappear in three to four years. There are many ways for hawks to die. Owls kill a few, 18% are hit by vehicles. A full 40% of hawk deaths Stewart investigated were the result of impacts with glass.
Windows take a toll, but glass sundecks are the number one killer of urban Cooper’s hawks. Hawks see a bird through the glass, fly at high speed to capture that prey, only to end up dead on someone’s deck. Hawks do not recognize glass as a barrier. Stewart suggests homeowners and businesses make it clear a barrier exists by placing a cedar lattice in front, above or behind windows and sundecks to establish a grid pattern. Streamers can be helpful in large quantities but decals on windows are "totally ineffective."
If nest trees are impossible to climb, or nest aren’t discovered, some nestlings go unbanded and Stewart must spend more time and effort catching flying hawks with traps or nets. In the left photo below, Andy and helpers wait hours to capture a fledgling juvenile in the Heywood Meadow area of Beacon Hill Park. Andy holds a young male caught and banded at last in the photo on the right. A live brown-headed cowbird inside a “bal-chatri” trap enticed the hawk to land where his feet became tangled in nylon nooses. Andy, on alert nearby, hurried immediately to safely free and band him. (Photos by Norm Ringuette)
Home chores and social life are on hold for Stewart from February through August, the busiest months for hawk research, but work continues all year. He tracks movements, responds to calls about dead and injured birds and keeps meticulous records. The shelves in his small home office are loaded with data notebooks. Stewart struggles to find minimal funding. In 2008, colour bands cost him $7 each; arborists who climb trees for him must be paid.
No fame or fortune lies ahead. Andrew C. Stewart has the respect of other researchers and the satisfaction of knowing he is making an important contribution. That will have to suffice.
You can contribute to the hawk study by reporting all sightings of banded Cooper’s Hawks to Andy Stewart. If possible, record the band colour and code, date, time and location. Even if you are unable to determine the band code, band colour in itself provides very useful data. Contact: firstname.lastname@example.org