I get into a lot of arguments with my best friend’s mother, but the biggest bone of (hopefully good natured*)contention between us revolves around the migration patterns of robins. She, like many other people in eastern North America, considers the arrival of robins to be a sign that spring has sprung.
The point I take issue with is that, in the northeastern US, many robins don’t actually leave during the winter. Well, they leave your backyard, because it is covered in snow and doesn’t provide resources (unless you have a tree with berries), but most of the population stays right where it is.
For example, this image shows you the “first robin sighting” across North America (most of these are citizen scientists reporting robin sightings)
The triangles are robins seen before Feb 22, and they are distributed across the northeastern US and even into Canada. Populations in northern Canada do migrate and some are not seen until mid-April (dark blue dots). Although “first robins” are seen later in the spring across the northeast also, people don’t always detect them when they are present. You can see there’s at least one point in Florida where a citizen scientist didn’t notice a robin until March. This has a lot to do with the fact that robins subsist on fruit during the winter, and they are highly mobile, moving from one fruit source to the next.
So, yes, the arrival of robins in your backyard, eating worms from the grass IS a sign of spring, but it’s not because robins have left the country for the winter. It’s because they left your yard.
My friend’s mom still won’t believe me on this point, but we’ve decided to agree to disagree and sometimes it’s important not to sweat the details of robin migrations.