What specific event might cause a Red-breasted Nuthatch population to move south?

Answer

Failure of cone crops in northern coniferous forests (an irruption)

The Red-breasted Nuthatch is more nomadic than other species and will sometimes move south if the cone crops, which are a primary food source, fail in their northern coniferous homes.

What specific event might cause a Red-breasted Nuthatch population to move south?
birdanimalWintermigrationNuthatch