why don't swallows and other migratory birds stay in their wintering places all year round?

I understand why they would migrate to avoid our winter but why bother coming here at all with the risks it involves

  • I believe the main reason is the daytime length here during summer. They have many more daylight hours available to them when feeding and raising their young than they would have nearer the equator where daytime and night time are generally nearer 12 hours each all year round. They move back south as the cold weather creeps in here and the insects they feed on diminish (in the case of Swallows).

  • It will be very much an environmental thing as to why these birds migrate many thousands of miles, not just to raise young, but for food and also to provide food for other species!

    Nature can be harsh and many don't make the long migration, and either through ill health or otherwise die, or more likely, as they pass over the continents, become prey to larger birds.

    The cycle of life, which helps to keep numbers in sensible proportions (until man intervenes) while supporting other species.