Despite their name, mayflies emerge from their aquatic homes in swarms throughout the summer. This final part of their lifecycle is brief, but their synchronized emergence creates a valuable food pulse for nearby insectivorous birds.
A 2020 research study used radar surveillance data to measure mayfly abundance and found that along the Upper Mississippi River and Western Lake Erie Basin, a single mayfly emergence can produce almost 88 billion mayflies (3,000 tons of biomass). Annually, mayflies represent 12 trillion calories capable of supporting over 53 million nestling birds.
The lead researcher notes, "Therefore, we can assume these insects have a nearly instant impact on the birds that survive on them when they descend on their respective shorelines."
While these numbers seem staggeringly big, persistent declines in mayfly abundance indicate unhealthy changes to waterways which may ultimately hurt birds. The authors of this study found a decrease of more than 50% in mayfly populations from 2012 to 2019 in their study area.