This was quite a promising line of attack, but, since the state of ecological knowledge was low, and since in any case it was based on the false premise that everything in Nature must be ultimately beneficial to man, it often led to circular arguments. Why, to help the gardener, by keeping down aphids. Why, to feed ladybirds, of course. This solution was deemed sufficient. The Dynamics of Life.
Birds help to maintain balance in the environment.
Some birds eat insects that would otherwise increase in number so much that they would overwhelm natural habitats. Predatory birds feed on rats and mice and keep them in check. As predators, sharks keep prey populations healthy by limiting the sizes of the populations. Without sharks, prey species would increase in number and be subject to starvation and disease. So again, mystical foolishness.