Every night across eastern New South Wales, weather radars are lighting up with what looks like widespread light rain. There is no rain. The signals are bogong moths — millions of them — on their annual migration to the Australian Alps, their bodies and wings bouncing back radar pulses designed for water particles. The Bureau of Meteorology confirms the effect is plausible, though temperature inversions can produce similar echoes. The bogong moth hasn't been seen in these numbers for years. Populations collapsed in recent seasons, and while the current swarms through Sydney and Canberra have thrilled residents, Dr Kate Umbers of Western Sydney University cautions that urban abundance doesn't necessarily equal a population boom. Their alpine habitat remains under pressure from global heating. The species is not out of danger. What makes this story structurally interesting is the radar data itself. Umbers calls it "absolute gold." Researchers have spent years trying to trace bogong migration routes using moth tags, newspaper clippings, and citizen reports — all expensive, patchy, and slow. The radar data already exists. It covers hundreds of kilometres. It runs every night. The infrastructure cost was already paid by the Bureau of Meteorology for weather forecasting. Prof Justin Welbergen at Western Sydney University has already proven the concept with flying foxes. His team built a working prototype called Aerocast that uses weather radar to track and count bats — in near real time via algorithm, and retrospectively using decades of archived station data. Flying foxes register as "a big bag of water" emerging at dusk from predictable roosts. The technique revealed that their departures are socially organised: hungry females first, then young, then males last. The American equivalent, BirdCast, uses the same principle to track bird migrations across the continental United States. Welbergen wants to expand Aerocast to cover birds and bogong moths, noting that on radar, "flying foxes are effectively just giant moths." The shared signal characteristics — predictable locations, predictable timing, detectable biomass — make the methods transferable. The conservation potential is real but dependent on radar coverage and data quality. Weather radars were not designed for this. Disentangling moth echoes from temperature inversions, bird movements, and actual precipitation requires algorithmic sophistication. But the raw infrastructure already blankets eastern Australia, and Welbergen's flying fox work demonstrates that the signal extraction is solvable. Umbers has meanwhile enlisted millions of involuntary research assistants — Sydney and Canberra residents reporting sightings — creating a crowd-sourced dataset that complements the radar. The moths, she says, are saying: "Don't forget about us, look after us, look how amazing and impactful and epic we can be." The question is whether this convergence of public attention, radar data, and algorithmic tools translates into durable monitoring before the next population crash.
