Here's the scoop. There are several factors at play. First off, we're doubled up on robins. Our summer resident robins mostly move south in the winter in search of food. Robins from further north, and I mean all the way up into Canada, also moved south this winter. Some of them went past the Twin Cities while some of them formed winter flocks and hung out around open water and ornamental fruiting trees. The slow start to spring and continued fowl weather including lots of snow up north has put a halt to migration. Pretty much the entire Mississippi Flyway's worth of robins are backed up in the Twin Cities right now. These are resident birds mixed in with a sizable percentage of all the birds in Canada.
Like us, they are simply waiting for the weather to improve. This is about as far north as they dare go at this point.
I do believe there is one other factor at play and it has to do with freakish weather. We have a late spring this year but and unbelievably early spring last year. It was already in the 70s in March last year and many birds were very successful at nesting. I heard reports of many species laying an entire extra clutch of eggs over the course of the season. What we may be seeing here is a combination of the backing up of migrating birds combined with a higher than normal population of birds.
Jason DeRusha just did a Good Question segment on this topic and it featured my buddy Sharon.