A new study shows that a widespread decline in the incidence of newly emerged insects – whose immature stages develop in lakes and streams while adults live on land – may help offset the alarming decline in the abundance and diversity of insectivorous aerial birds (i.e. the Hunting for flying insects) in the USA. The decline in the number of new insects appears to be due, in turn, to disturbance and pollution of water by humans, especially in streams. This study, published in Frontiers in Ecology and Evolution, is one of the first to find evidence of a causal link between the decline in insectivorous birds, the decline in new aquatic insects, and poor water quality.
Human activities such as urbanization and agriculture have a detrimental effect on aquatic ecosystems. In the US, 46% of streams are in poor condition while 57% of lakes suffer from severe human disturbance. The immature stages of aquatic insects, particularly stoneflies, mayflies and caddis flies, are known to be very sensitive to pollution, which is why they have been widely used as bio-monitors for water quality. However, the authors of the present study predicted a priori that emerging insects – whose adult flight stages are important food sources for birds, spiders, bats, and reptiles – should also be powerful bio-monitors for terrestrial ecosystem health. This prediction is confirmed by the new results.
“The massive decline in avian fauna in the US requires the introduction of new paradigms for conservation. Currently, most management and conservation agencies and plans are divided into aquatic and terrestrial areas. However, aquatic and terrestrial ecosystems are inextricably linked by a number of ecological factors Connections, “says the author Dr. Maeika Sullivan, Associate Professor at the School of Environment and Natural Resources and Director of the Schiermeier Olentangy River Wetland Research Park at Ohio State University.
Sullivan and colleagues analyzed data from several open access surveys for monitoring water quality, aquatic invertebrates, and 21 species of insectivorous airbirds from the neighboring United States. “The task of compiling these large amounts of data, which had been collected by various US agencies with different goals, resulted in several new questions and challenges that require interdisciplinary thinking to be solved,” says the corresponding author Dr. David Manning, Assistant Professor in the Department of Biology, University of Nebraska, Omaha.
First, the authors show that water quality is a good predictor of the local relative abundance of emergent insects. Then they show, for the first time, that water quality and the associated incidence of emerging insects explains a moderate but significant proportion of the variation in local insectivorous airbird abundance in the United States, including upland and bank species (i.e., foraging on river banks).
Not all bird species were equally affected by decreases in the incidence of new insects, suggesting that factors such as the birds’ microhabitat and foraging strategy may also play a role. The western forest pewee (Contopus sordidulus, a highland bird species), the olive-sided flycatcher (C. Cooperi, who lives optionally in riparian zones) and the Acadian flycatcher (Empidonax virescens, which occurs almost exclusively near water) were most dependent on the local population Frequency of total emerging insects. The eastern phoebe (Sayornis phoebe), the purple-green swallow (Tachycineta thalassina), the tree swallow (Tachycineta bicolor), the eastern forest swallow (C. virens), the barn swallow (Hirundo rustica) and the chimney swallow (Chaetura pelagica) were particularly sensitive to the relative frequency of stoneflies, mayflies and caddis flies.
The authors emphasize the need for interdisciplinary research to develop new conservation and biomonitoring strategies that focus on the effects of water quality on endangered birds and other terrestrial animals.
‘We need a better understanding of the common mechanisms that can cause declines in both aquatic insects and many bird species. We want to explore some of these common mechanisms in future research, but on a much larger scale than before. Tackling these questions will to do.” require collaboration between freshwater ecologists, ornithologists, landscape ecologists, entomologists, data scientists and others, “says Manning.
###
Disclaimer: AAAS and EurekAlert! are not responsible for the correctness of the press releases published on EurekAlert! by contributing institutions or to use information through the EurekAlert system.
