The study analyzes data from 140 weather surveillance radars that routinely scan the sky for clouds and precipitation but also detect signals from birds, bats, insects and other flying organisms. In this work, the team focused on the component of the signal attributable to insects, using archived radar data provided open access by the US National Oceanic and Atmospheric Administration (NOAA) to derive daily estimates of insect abundance between 2012 and 2021.
Monitoring aerial insects over large regions has been difficult because most existing surveys track only selected species and rely on local sampling methods. The radar-based approach offers automated, continuous coverage over broad areas and allows scientists to construct a ten year time series of flying insect abundance for the entire mainland US. The authors note that this new data source helps fill a major gap in understanding how environmental change is affecting insects that spend part of their life cycle in the air.
Across the contiguous United States, overall insect abundance in the airspace appeared relatively stable over the ten year period studied. At the same time, individual radar sites showed marked regional variation, with roughly half of the locations indicating increased insect density and the other half indicating declines. This spatial pattern points to local and regional drivers that affect insect populations differently rather than a uniform national trend.
Changes in winter temperature showed the strongest statistical link to these regional fluctuations in aerial insect numbers. In areas where winters warmed more over the study period, radars tended to record the largest declines in insect density. The researchers point out that many aspects of insect life history, including hatching, development and susceptibility to parasites, are closely regulated by temperature, so shifts in winter conditions can alter survival and reproduction in complex ways.
The radar record also has important limitations for documenting long term trends in insect populations. The authors emphasize that some of the most severe declines in insects may have occurred between the 1970s and 1990s, before the time window covered by the NOAA radar archive used in this analysis. In addition, weather radars cannot distinguish among insect species, so a stable total biomass in the air could mask losses of species that are more sensitive to environmental change if they are being replaced by more tolerant or abundant species.
To resolve these issues, the researchers argue that radar based monitoring should be integrated with other sources of biological information. These include on the ground surveys, targeted sampling programs and citizen science observations that can identify species and track changes in community composition. Combining these complementary data streams would allow scientists to link the large scale patterns seen by radar with detailed information on which species are increasing or declining in different landscapes.
The team also sees potential to extend this approach beyond North America. In many regions of the Global South, there are far fewer systematic surveys of insect diversity and abundance than in Europe and North America, leaving major gaps in knowledge. Because many countries already operate networks of weather radars for meteorological purposes, applying similar analytical methods could rapidly expand monitoring of flying insects in under sampled parts of the world.
Reanalysis of historical radar data with updated computational models could further reveal how aerial insect populations have changed over previous decades. As algorithms for separating biological signals from precipitation and other targets improve, older radar archives may yield new insights into past shifts in insect biomass and migration patterns. The researchers suggest that such long term records will be important for assessing the ecological consequences of climate change, land use shifts and other human driven pressures on insect populations.
Research Report:Systematic Continental Scale Monitoring by Weather Surveillance Radar Shows Fewer Insects Above Warming Landscapes in the United States
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