Understanding declines of aerial insectivores in North America

 A growing body of research demonstrates that aerial insectivores as a group are undergoing population changes, and in some species (nightjars, some swallows) are experiencing population declines.

The following papers describe some of what has been learned:

Evidence for multiple drivers of aerial insectivore declines in North America

Kimberly J Spiller, Randy Dettmers.
The Condor, Volume 121, Issue 2, 1 May 2019

https://academic.oup.com/condor/article/121/2/duz010/5497088

 "Aerial insectivores (birds that forage on aerial insects) have experienced significant population declines in North America. Numerous hypotheses have been proposed for these declines, but current evidence suggests multiple factors could be operating in combination during their annual migratory cycles between breeding and nonbreeding areas. Potential drivers include decreased prey abundance, direct or indirect impacts of environmental contaminants, habitat loss, phenological changes due to warming climate, and conditions on migratory stopover or wintering grounds."

 

 Nebel, S., A. Mills, J. D. McCracken, and P. D. Taylor. 2010. Declines of aerial insectivores in North America follow a geographic gradient. Avian Conservation and Ecology - Écologie et conservation des oiseaux 5(2): 1. [online] URL: http://www.ace-eco.org/vol5/iss2/art1/

Kevin C Fraser , Bridget J M Stutchbury, Cassandra Silverio, Patrick M Kramer, John Barrow, David Newstead, Nanette Mickle, Bruce F Cousens, J Charlene Lee, Danielle M Morrison, Tim Shaheen, Paul Mammenga, Kelly Applegate, John Tautin.  2012. Continent-wide tracking to determine migratory connectivity and tropical habitat associations of a declining aerial insectivore. Proceedings. Royal Soc. B.2794901–4906

https://royalsocietypublishing.org/doi/full/10.1098/rspb.2012.2207#d62867049e722s