in the article they say: 

"80 percent of the time it was a secondarily affected creature that was the first to disappear."

in other words, animals that depend on insects, should exhibit decline before the insects are gone. So, I looked into bird declines, which would be expected if their food source was declining

ABSTRACT

North American birds that feed on aerial insects are experiencing widespread population declines. An analysis of the North American Breeding Bird Survey trend estimates for 1966 to 2006 suggests that declines in this guild are significantly stronger than in passerines in general. The pattern of decline also shows a striking geographical gradient, with aerial insectivore declines becoming more prevalent towards the northeast of North America. Declines are also more acute in species that migrate long distances compared to those that migrate short distances. The declines become manifest, almost without exception, in the mid 1980s. The taxonomic breadth of these downward trends suggests that declines in aerial insectivore populations are linked to changes in populations of flying insects, and these changes might be indicative of underlying ecosystem changes.

Declines in aerial insectivore songbirds were first noted about two decades ago (Böhning-Gaese et al. 1993) and have continued to this day. Our analysis of North American Breeding Bird Survey trend estimates shows that passerines of the aerial insectivore guild incurred significantly stronger declines between 1966 and 2006 compared to other passerines. Furthermore, we show a striking geographical gradient in the population trends of aerial insectivores, with the probability of decline being the highest in northeastern North America. Declining trends predominate after 1980 and are most acute in species migrating to and from South America. 

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 

Peter 🐝

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