Alberta Golden Eagles Part II / by Jon Groves

Alberta golden eagle nesting pair. Note the deer fawn leg and mallard remains on the nest.

Alberta golden eagle nesting pair. Note the deer fawn leg and mallard remains on the nest.

In early July the two eaglets were banded, an older male and younger female. This was the first year where this nesting pair produced two young, food resources were likely plentiful. A week after banding I went out to check the nest and couldn't see either eaglet on the nest or in the area. I was alarmed because the eaglets were still mostly down-covered and incapable of flight. Furthermore, there were no visible prey remains in the nest so I assumed a feline predator managed to climb in and raid the nest. The nest was normally littered with prey remains and the smell of decaying mallards and deer baking in the summer heat would surely attract predators and scavengers. There aren't many mammalian predators capable of accessing this cliff nest and they certainly aren't common in this area of Alberta but I immediately blamed a bobcat or cougar for wiping out the young.

I couldn't see anything from the cliff top so I decided to hike up the river and have a look under the nest. I was relieved to see both eaglets sitting below the cliff along the river bank trying to find some shade. There is a possibility something spooked them off the nest at night but it seems more likely that the young bailed off the nest to escape the summer heat. The nest location offered no shade during the heat of the day and the young were large enough where the female couldn't efficiently provide shade for them anymore. In addition to the eaglet's increasing size, their food demands were also rising substantially and both adult eagles were hunting now to meet the demand.  The young male eagle was much more mobile at this point than his larger more cumbersome sister but it was clear by the visible prey remains that the eaglets were still being fed in situ by the adults. The adults were rarely seen around the nest at this stage of the nesting cycle and they both spent considerable time hunting, often cooperatively. I managed to witness two successful hunting flights at ravens. Ravens are extremely aerial and adroit on the wing but it seems they aren't much of a match for a pair of hungry golden eagles. 

The eagles were out below the nest for almost two weeks when a massive storm system passed through the area dropping almost five inches of rain in 24 hours. The day after the deluge of rain I hiked up the valley to check how the eagles were faring. I first noticed how much the river had risen as I approached the nesting territory, it was also loaded with silt and sediment from the tremendous runoff in the area. Because the cliffs and banks in the river valley are predominately clay and exposed soil, they are much more prone to erosion than rocky outcroppings. As I rounded a bend in the river I could see the young male perched in his usual spot but I couldn't see the female. I could see a massive soil slump near the area where the eaglets had been hanging out, and the slump was so large it blocked the entire channel and this explained the high water level I noticed when I hiked in from the upstream side. When I got closer I could see the body of the female eagle among the soil and debris that slid into the river so I swam across to retrieve her. The female eaglet had a large contusion on the back of her head and must have been struck when the soil came cascading down the cliff during the heavy rain. Raptors often succumb to vehicle collisions, electrocution, and colliding with man-made objects but it was a natural occurrence that killed the young female eagle brought on by rare stochastic weather event. More rain was received in 24 hours than the whole month of July on average. The pair of eagles managed to successfully fledge the young male and he was seen with the adults as late as October. 

Adult female golden eagle with two eaglets on the nest. The younger but larger female eaglet showing far less feather development than the older male in the background. 

Adult female golden eagle with two eaglets on the nest. The younger but larger female eaglet showing far less feather development than the older male in the background.