Changes in the biodiversity of various ecosystems around the world often happen slowly, imperceptibly, and it can be difficult to know what’s even been lost over years and decades—there’s simply no baseline to compare against. But tucked away in a small liberal arts college in Eagle Rock, California is a scientific collection that’s helping to make this type of assessment possible. The Moore Laboratory of Zoology houses the largest collection of Mexican birds in the world—more than 65,000 specimens, most of which were collected by one man, Chester Lamb, between 1920 and 1960. In essence, the collection provides a snapshot of Mexico’s bird biodiversity from a time prior to the country’s industrial revolution and the significant habitat loss and degradation that ensued during that period. Using this one-of-a-kind tool, Moore Lab curator, John McCormack, and colleagues are retracing Lamb’s footsteps and conducting their own surveys to learn how and why Mexico’s bird fauna has changed over time—as well as how some species might be adapting to ecosystem-scale transformations.