Decoding the diet of a declining aerial insectivore

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Beverly McClenaghan


Aerial insectivores, a group of birds that feed on insects in flight, are the fastest declining birds in Canada, with population declines of up to 80%. The cause of these declines is unknown but a decrease in their common food source – flying insects – has been suggested as a potential driver of the population declines. Barn swallows (Hirundo rustica), a species of aerial insectivore, have declined by 66% in Ontario, where they are listed as a species at risk. Without knowing what insects barn swallows eat, it is hard to determine whether a change in their food supply is contributing to their decline. My project is using innovative DNA sequencing techniques to determine what insects barn swallows are eating and to determine whether food availability is affecting their reproduction. My results showed that barn swallows consumed a very broad range of insect species, while choosing larger insects over small insects, and they showed flexibility in their diet in response to changing food availability. There was no relationship between food availability and reproductive behaviour during the breeding season. This suggests that the barn swallow population size is not currently limited by food availability on the breeding grounds. Additionally, barn swallows should be able to take advantage of changing food resources. While we still do not know the cause of the population decline in barn swallows, these results give us information on which resources need protection to conserve barn swallows in Ontario.

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