Here's a breakdown:
* Food availability: Wagtails primarily feed on insects. As winter approaches in their northern breeding grounds, insect populations decline significantly. To survive, they must travel south to warmer regions where insects remain abundant.
* Breeding grounds: Wagtails need suitable nesting areas and ample food to successfully raise their young. These conditions are more readily available in warmer climates during the breeding season. The warmer temperatures and longer daylight hours also contribute to successful breeding.
Here's how it works for wagtails:
1. Spring: They migrate north from their wintering grounds to their breeding grounds, taking advantage of the abundance of insects and suitable nesting sites.
2. Summer: They breed and raise their young in these northern regions.
3. Autumn: As the weather cools and insect populations decline, they migrate south again, seeking food and warmer temperatures.
4. Winter: They spend the winter in their southern wintering grounds, typically in warmer regions like Africa or southern Europe.
Note: Not all wagtail species migrate. Some species, like the pied wagtail, are resident birds, meaning they stay in the same area year-round. However, even resident wagtails may undertake short, local movements in response to changing food availability or weather conditions.