Aerial insectivores are victims of widespread pesticide pollution - Canada's native bird population trends tell the story

Canada is home to billions of birds belonging to some 451 regularly occurring native species that raise their young or spend their non-breeding seasons in this vast and varied country. Increasingly, these birds face many threats here and elsewhere. On average, Canadian breeding bird populations have decreased 12% since 1970 when effective monitoring began for most species. Some groups, such as grassland birds, aerial insectivores and shorebirds, are showing major declines. Aerial insectivores—birds that catch insects in flight—are declining more steeply than any other group of birds. Some formerly very common species like the Barn Swallow and Chimney Swift have declined to less than a quarter of their 1970-level populations.

Source: The State of Canada's Birds 2012
http://www.stateofcanadasbirds.org/overview.jsp