This past summer I spent considerable time observing and photographing a nesting pair of golden eagles in southern Alberta. These golden eagles nest in the Rosebud River valley as it carves through a landscape dominated by cultivation, alternating between cliff and tree nest locations in some years. These eagles are unique because golden eagles are typically found at a relatively low densities in ideal habitat and normally absent from areas heavily disturbed by modern agriculture or development. My goal with this endeavor wasn't only to get some unique photos of nesting golden eagles but to observe the behavior of the breeding pair. I was particularly interested in what sort of prey they were exploiting and the remote camera was successful in answering some of my queries.
The eagles are year-round residents in the area with courtship activities and nest building initiated in mid-February. For the 2015 breeding season a cliff nest used previously was chosen and the female began incubation on April 1st. Early on I had planned on photographing nesting activities through the use of a remote camera setup that I could trigger from a long distance while observing with a spotting scope from a kilometer away. Golden eagles are particularly sensitive to disturbance near the nest site so it was imperative that a remote camera setup be used.
Through photos and feather collection around the cliff tops at the nest site it was clear that these eagles were primarily killing avian prey, mostly waterfowl. I watched the male eagle bring in numerous mallards and saw him on several hunting sorties while soaring thousands of feet over the river valley. Golden eagles are able to exploit a broad prey base and most studies show that eagles are extremely adaptable to whichever species is abundant in the area. In agricultural landscapes near the Rosebud River mallards are numerous during the spring nesting season and are particularly vulnerable to predation as they wander cultivated fields in newly formed breeding pairs. Because of his colorful spring breeding plumage the drake mallard is at much greater risk compared to the more cryptic hen. The male eagle had a taste for drake mallards but I also observed gull, raven, magpie, and a mule deer fawn brought into the nest.
During the early brood rearing period the female eagle spends virtually all her time on or in areas immediately surrounding the nest site while the male brings in prey. Because the cliff nest is south facing the female spent much of her time shading her young from the summer heat. This south facing location makes for challenging photography conditions because of the harsh summer light but also from heat diffraction coming off the cliff face. The use of a telephoto lens during these conditions is an exercise of futility with heat waves rendering images painfully blurry. Cloudy days provided for the best photography conditions but we don't seem to get many in sunny southern Alberta. As the young grew to where they could thermoregulate with greater efficiency, the female began to hunt as well, at this point the pair would often hunt cooperatively, no bird is safe when a pair of eagles hunt together.
Late morning in in mid-June the male eagle was soaring high over the territory while the female sat on a cliff top near the nest. I was watching through a scope from a kilometer away after setting up the camera early in the morning. I hadn't observed any cooperative hunting flights at this point of the breeding season but I was in for a treat this day. As I watched the female in the scope while keeping an eye on the soaring male I noticed the female take off the cliff top and disappear over the bank. I didn't think much of it until I looked up at the male in a full stoop hurtling towards the valley below. I hurriedly grabbed my binoculars to follow the male downwards as he raced towards the earth at breakneck speed. He leveled out and abruptly shot to the side as if fired from a slingshot before merging with a large white bird over the badlands. His prey dodged but the female now showed up chasing in tandem with the male as he used the momentum generated from the first stoop to dive upon the bird again. Initially I thought their quarry was a large gull but I soon determined they were chasing an osprey. This wasn't a nest defense scenario, they were intent on killing the osprey to eat. The osprey managed to dodge both eagles numerous times before escaping into a stand of poplar trees in the valley bottom to avoid the onslaught. It was an incredible show of agility and power that eagles possess, they are an impressive predator capable or air superiority compared to virtually all birds out there, I'd be lying if I said I was cheering for the osprey on this occasion.