Hummingbird Migration 2024 Iowa City Ia. The johnson county spring migration count is held each year on the second saturday in may. The goal is to enjoy a day of birding at the peak of spring migration while tallying.

The fall migration is a journey south back to mexico and central america and starts when the abundance of insects (their main food source) starts to dwindle with cold temps. According to ryan, there are three main factors in bird migration.