Mass exodus

There was a big gathering of Brent geese on the green in Kilbarrack this morning.
All giddy and ready to head back to north east Canada.

Why they fly all the way here in the first place is beyond me (Tobago is 200 miles closer from Goose Bay than the Kilbarrack F.C. clubhouse...)
But if they like the place so much, and they obviously thrive here by the look of things (if the fat juicy droppings that they leave behind is anything to go by), why do they not become full time residents?

If a few pioneers were to stay behind for the other half of the year, they would discover that the weather that they love so much is actually the same ALL YEAR ROUND: shitty, damp, windy, mild-ish, with the odd sunny spell and truckloads of scattered showers.