Page 52 - EarthHeroes

Part of Doug’s team’s research was to study the effect of the wolves on the rest of the ecosystem – or all the living things, including plants and animals, interacting with each other in the park. While the team had expected elk numbers to fall, they were amazed by some of the other changes they discovered.
Firstly, the elk changed their feeding habits because of the wolves; they now constantly moved around to graze and browse instead of staying in one place. This, plus their reduced numbers, gave the land a chance to recover. When Doug first arrived, most willow and aspen trees had only come up to his knees
and had been badly damaged. Now cottonwood, aspen and poplar trees
grew again alongside the rivers, creating dense forests in previously bare valleys. With more trees came
more berries and insects, so then songbirds and migrating birds
returned. In the rivers, beavers, which had almost disappeared
from Yellowstone, started to flourish. Beavers feed on trees and use
them to build dams, which create deep pools where they fish in winter.
Ducks, fish, muskrats, reptiles and amphibians came to live in these pools.
Other species had benefitted from the arrival of the wolves too. Coyote numbers went down because wolves competed with them for food, and as a result the mouse and rabbit populations grew. This, in turn, attracted weasels, badgers, foxes and hawks, who feed on them. Ravens, bald eagles and bears flourished because they are scavengers, eating the leftover carcasses of animals killed by wolves. The bears also had more berries to eat. Cougars and bears increased the impact of the wolves by also killing the elk and their calves.
But the most surprising thing of all was that the wolves’ return had altered the flow of the rivers. In some places, the new trees stabilised the riverbanks with their roots, meaning the banks collapsed less, so those rivers became more fixed in their courses. In others, the beavers’ dams slowed down the rivers so that they
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