Re: Spring.
A Few Facts About Robin Migration
All robins are not the same: The vast majority of robins do move south in the winter. However, some stick around — and move around — in northern locations.
Robins migrate more in response to food than to temperature. Fruit is the robin's winter food source. As the ground thaws in the spring, they switch to earthworms and insects. While the robins may arrive when temperatures reach 37 degrees, this is because their food becomes available not because the robins themselves need warm temperatures.
Robins wander in the winter: Temperatures get colder as winter progresses. Robins need more food when it's cold and more and more of the fruit gets eaten. Robins move here and there in response to diminishing food supplies and harsh weather. If all robins wintered at their breeding latitude, there wouldn't be enough fruit for them all. So robins tend to spread out in the winter in search of fruit. Most hang out where fruit is abundant, but some take the risk of staying farther north where smaller amounts of fruit remain.
Robins sing when they arrive on territory: Robins sing when they arrive on their breeding territories. Sometimes robins even sing in winter flocks, due to surging hormones as the breeding season approaches. However, in the majority of cases, robins really do wait to sing until they have reached their territory.