https://www.scientificamerican.com/article/migrating-birds-may-be-collateral-damage-for-a-popular-pesticide/

One of the most widely used agricultural insecticides causes severe weight loss in white-crowned sparrows and delays the migration of these common North American songbirds, according to a new study published Thursday in Science. The finding suggests exposure to the pesticide could be contributing to declines in certain bird species over the past half-century, experts say.

The study examined the effects of imidacloprid, part of a class of neurological toxins called neonicotinoids used to target insect pests in farm fields. These chemicals, which can be directly applied to seeds and are absorbed into plant tissue as crops grow, were thought to be less toxic to vertebrates than other pesticides. When a neonicotinoid is applied to a seed, however, less than 20 percent of it will end up in the plant—and these pesticides are turning up in the environment. The chemicals have increasingly come under fire in recent years because their presence in the wild has been linked to losses of honeybee populations and implicated in birth defects among deer and other mammals.