Many birds and bats depend on insects that are disappearing

According to a new study from the University of Turku, birds, bats, and other insectivores may soon be struggling from a lack of food availability as insect populations continue to decline.

In collaboration with the Finnish Museum of Natural History, the team discovered that very distantly related predators are foraging in the same area of Southwest Finland for the same types of flies, mosquitoes, and other insects.

“It is striking how similar the dietary composition between the invertebrates, such as dragonflies and the vertebrates, was in the study. These results also raise concerns about what would happen if the small dipterans that all our focal predators harvest would decline,” said study senior researcher Kari Kaunisto.

The researchers found that chironomids serve as a common source of food for birds, bats, and dragonflies. There are up to 800 species of chironomids in Finland alone. These insects resemble mosquitoes and exist in large numbers on the surfaces of lakes and other water systems. 

With so many animals depending on chironomids to eat in overlapping habitats, the consequences would be far-reaching if they were to disappear.

“This is exactly what causes deeper concern. If many predators consume roughly the same food, the decline of chironomids, for example, could lead to an unprecedented ecocatastrophe,” said study co-author Eero Vesterinen, who has investigated species interactions and food webs for more than a decade. 

“I compared the material I had collected along the years with the studies I had published, and noticed an exciting pattern. It seemed that even though predators that prey on insects are placed in different parts of the animal kingdom, and therefore do not share the same evolutionary history, there are clear similarities in their diet.”

The team conducted a more precise analysis on the insectivores that were collected to compare the prey species available throughout the common area. 

The insectivores selected for the study were the European pied flycatcher, northern bat, brown long-eared bat, Daubenton’s bat, whiskered bat, Brandt’s bat, black darter, common spreadwing, northern bluet, spearhead bluet, crescent bluet, and variable bluet.

“The majority of all the bats in the world are insectivores, and our previous studies have already revealed many significant details about their diet,” noted Thomas Lilley from the Finnish Museum of Natural History.

In some places, the insect population has collapsed to under 50 percent, and similar incidents are being reported worldwide. 

“The situation may be worse than previously estimated, if the results of the new study can be generalised intercontinentally,” said Vesterinen. “Our study seems to have produced different and elaborated data that helps us focus our future research on the phenomenon’s cascade effect higher in the food chain.”

The study is published in the journal Scientific Reports.

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By Chrissy Sexton, Earth.com Staff Writer