White-crowned Sparrow. Photograph by Bettina Arrigoni (CC BY 2.0)

It is a tough world out there if you are a migratory bird. Loss of habitat for breeding, migration, and wintering can force compromises in vital life events. So can reduced food supplies due to invasive plants, agricultural practices, urbanization, climate change, and other blights. The likelihood of death by feral cats, other human-increased mammals, glass windows, automobiles, and adverse weather, not to mention disease and disability, increases with longer stopover time as well. If you noticed agricultural practices on the above list, let me tell you about an interesting paper I read recently from a research group I have written about before (Larson 2018).