Birds that commute

Everyone knows about migration, the great seasonal journeys. Less noticed is the daily version: the starlings, gulls and crows that leave a roost at dawn, fly to the places where the food is, and return at dusk, along routes so regular that people who live under them can set a clock by the noise.

The commutes are long. Some gulls fly fifty kilometres each way to a landfill and back to a reservoir. The timing shifts with the daylight, not the clock, so the morning flight moves by a minute or two a day through the autumn, which is how one researcher noticed it in the first place.

What the birds are optimising is not speed but safety: the roost is where the predators are not, the food is where it is, and the distance between them is a cost worth paying. Anyone who has chosen a longer commute for a quieter home will understand.