We know that climate change is affecting animals and habitats across our world, but figuring out how isn’t always easy. In fact, for years, I told audiences we simply could not know how mountain birds in the Pacific Northwest were responding to climate change. But as my recent research proves, I was mistaken.

It wasn’t for lack of scientific interest — biologists worry that mountain species are vulnerable to warming temperatures. It wasn’t for lack of personal interest — I grew up among the snow-capped mountains of the region and wanted to know what was happening in my own backyard. It was because we lacked the data.

Specifically, I thought there was no historical data describing where Pacific Northwest birds lived along mountain slopes prior to recent climate change. Historical data provides a crucial baseline. With good historical data in hand, researchers can compare where species live now to where they used to live. In protected landscapes where people aren’t directly changing the habitat, climate change is the main force that could impact where birds live.

As a postdoctoral fellow at the University of British Columbia, I had found historical datasets and conducted resurveys in far-flung locations from Peru to

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