It’s hard to keep wild animals out of farms. Birds, mammals and insects all affect crop yields, in positive ways (such as flies pollinating flowers) and negative ones (such as when birds damage fruit).
Agricultural research and management programs often deal with these interactions by focusing on simplistic “good” and “bad” labels: aphids are annoying pests, for example, whereas bees are little angels.
And see the papers behind the article here:
Saunders ME, Peisley RK, Rader R, Luck GW (2016) Pollinators, pests, and predators: Recognizing ecological trade-offs in agroecosystems. AMBIO 45:4-14.
Peisley RK, Saunders ME, Luck GW (2015) A systematic review of the benefits and costs of bird and insect activity in agroecosystems. Springer Science Reviews 3:113-125.