Red-winged blackbirds are the first to show up.

They don’t check a calendar. Melting snow and longer daylight tell their bodies it’s time, thanks to an internal clock tuned to day length. Hormones kick in, fat stores build, and off they go.

Different species respond to slightly different cues. The early birds—redwings, grackles, robins, killdeer—are short-distance migrants that can handle a cold snap. They start moving when days hit a certain length, even if it’s still freezing. Warblers and swallows wait for insects, which wait for warmer weather.

So yes, the birds know because their bodies measure light. And if you want the first sign of spring, look for the red-shouldered flash in the marshes.

They show up before the robins, honestly.