Hummingbirds like other birds are triggered by day length to start their migrations. Because flying is so costly on a bird’s body, they have to fatten up to survive their nightly flights (one reason they defend feeders so vigorously this time of year).By keeping your feeders out and filled late into the fall, you may help a late migrating bird that is coming through when natural food is truly scarce. In the past few years, we have consistently gotten reports of hummingbirds at feeders through the first week of October.