While the whole nation is paying plenty of attention to the human toll of the state’s ongoing drought–its worst in history, California’s wildlife is suffering far more quietly. And no one knows that better than Bernie Krause, a pioneer in the small but growing field of soundscape ecology who, since 1968, has made recordings in more than 2,000 types of habitats around the world.

Krause lives in Glen Ellen, California, where he stores his priceless archives and runs his organization, Wild Sanctuary. In recent years, and especially in his recent book, Voices of the Wild, he has attempted to call the world’s attention to the declining diversity and richness of nature’s sounds–an often overlooked proxy for measuring the overall health of wild ecosystems.

His work has taken him around the world, from the Amazon’s rainforests to Alaska’s Glacier Bay. But Krause’s 20 years of recording near his Northern California home are what’s concerning him most lately. The clip below, shared exclusively with Co.Exist, illustrates through sound the dramatic effect of environmental degradation in one location over time.

Listen to the audio, captured at California’s Sugarloaf State Park over the last 11 years. Years of record-low rainfall and the earlier arrival of spring has, to Krause, turned the loud sounds of spring to what seems more like a winter’s quiet day.

“This year–because of the drought–we experienced what was virtually a silent spring with no birdsong for the first time in living memory–even at what would have normally been the height of the season in mid-April,” he says.

Audio recordings by Bernie Krause, courtesy of Wild Sanctuary. © 2015 Wild Sanctuary. All rights reserved.

Since 1994, Krause had been recording the same location at Sugarloaf State Park in mid-April, using the same equipment and carefully calibrated settings and protocols. The video presents four 15-second sound samples captured in 2004, 2009, 2014, and 2015.

The lower half of the spectrogram shown in the video represents the sound signature of a stream that was flowing normally in 2004 and 2009, but had run dry in more recent years. The upper half represents the vocalizations of several bird species. Krause’s recordings prior to and including 2004 all indicated similar bird density and diversity. But between 2004 and 2009, the density dropped off slightly. Krause thinks that’s due to the spring season temperatures moving in two weeks earlier on average in the area, but at least the stream is still flowing.