Why Do Birds Migrate?

This pair of tree swallows was dive-bombing me while out turkey hunting the other day.  It's the nesting season.

This diminutive little bird usually arrives in late March or early April following a winter stay in the Gulf Coast, Cuba or Guatemala. 

Why in the heck would any self-respecting song bird travel such a great distance instead of staying in the inviting climate of the Gulf Coast?

The answer is that many birds do not migrate.  It is believed that as many as four-fifths of all birds remain in the tropics year-round.  The theory about migrants has much to do with the availability of food.

If all birds remained in their tropical winter habitat food resources might grow scarce under the pressure of raising a family.  In the northern latitudes food resources are abundant three seasons out of the year.  Moreover, the days are longer and with longer daylight it is easier to feed a hungry brood.

Summer in the arctic region is awash in a swarm of insects and daylight is all day long.