It might feel like the height of summer where you live, but bird migration is already in full swing for many species, and others are preparing for their upcoming trip. Birds use the shortening days (the photoperiod) as a cue that it’s time to head south, and cooler temperatures and decreasing food supplies also help birds determine the right time to launch into the sky for their southward journey.
Birds often use different routes for their spring and fall migrations, forming what looks like a clockwise loop to their movements. These route changes allow birds to take advantage of seasonal wind patterns and habitat differences. It also means that the migrating species you spotted in the spring may not visit again soon, while different species may be heading to you right now.
Even with an advantageous route, fall migration is a perilous time for birds, especially for young birds making their first migratory journey. New research suggests that light pollution, urban and suburban areas, livestock management and agriculture can impact fall-migrating warblers. Other research shows how extreme weather events such as heightened wildfire activity and drought can negatively impact fall migrating birds’ health, and how birds are adapting their fall migration patterns in response to climate change.