Most salmon return to spawn as adults in the same streams they were born in — but some don’t. Salmon that spawn elsewhere are said to have ‘strayed’ and the exact reasons for why salmon stray is often a mystery. Understanding the reasons are important though, because the straying between otherwise independent populations can have synchronizing effects, and affect future population viability. Some recent work I helped with led by Peter Westley at UAF investigated multiple climate and human hypotheses for why Chinook salmon from the Columbia River stray. Using long term data from 19 populations, we found that warmer temperatures and smaller population sizes may be good predictors of salmon straying.