Manco inca Yupanqui (1516-1544) was made puppet Inca by Francisco Pizarro in 1533. Manco led the great Inca revolt and beseiged Cuzco in 1536.
The Incas ambushed and defeated four relief expeditions sent by Pizarro, killing almost 500 Spanish and capturing others, along with weapons, guns, armor and horses.
Defeated, Manco retreated to Vicabamba and founded the Neo-Inca State that lasted until 1572.
There were probably many places on the mountain trails leading to Cuzco that were good spots for ambushes, with mountains on one side and chasms on the other side.
I remember reading a review of a fantasy novel some time ago. It quoted a scene from the novel. An expedition of the 19th century Royal Navy was somewhat out of it's element in the high Andes mountains. The protagonist was a little girl who was important for some reason, and was escorted by a boy midshipman her age. The expedition was being attacked by flying creatures of some type and people were being carried away or knocked off the path to fall thousands of feet.
And I remember the Battle of the Five Armies in The Hobbit. When the eagles arrived they knocked goblin warriors off the mountain to their deaths.
So if the enemy is crossing the mountains and is on a narrow path with a chasm to one side, an attack by giant trained war eagles could spread panic and confusion. The goal would be to get people and especially animals to panic and stampede and knock each other off the path into the chasm. Perhaps they could slow down the mountain crossing of the enemy army until the campaigning season was about to end and they had to turn around and go back without accomplishing anything.
In a medieval society warriors often wear armor of some type, and mounted warriors often ride horses or other creatures that wear armor. but transportation animals, that pull wagons or carrying loads on their backs, don't wear armor because they don't go into battle. Thus it would be easy for giant war eagles to bite and claw the transportation animals and stampede them.
At the Battle of Glorietta Pass, New Mexico, on March 28, 1862, Rebel forces drove the Union forces back and captured the pass. But a Union detachment reached the Rebel rear and the rebel wagon train. They burned 80 wagons and their supplies, spiked the cannon, and killed or drove off 500 horses and mules.
Without their supply train the rebels eventually called off their invasion of New Mexico and retreated down the Rio Grande to Texas.
Destroying the enemy supply system can force them to abandon their campaign.