red-winged blackbirds return - a sign of spring

I was surprised to hear a red-winged blackbird today. Everything is snow covered and seems quite wintery still. I looked up when they returned to my yard in previous years:

2015: March 27
2016: March 5
2018: February 25
2019: March 12

I also looked at the site Journey North, a citizen reporting site. These dates fit with their observations. Some springs are late, some early. This looks like a pretty average one based on the blackbirds.