I have had a flock of 20-30 Pine Grosbeaks this winter at the feeders. But now there are only about 6 coming to the feeders and they are all females.
As with many birds, the males migrant to the breeding grounds first. They set up territories and wait for the females to arrive. That might be the case with the Pine Grosbeaks. Most all of them have left northern Minnesota by March 15th. It’s a sure sign of spring, even though there might still be lots of snow on the ground and a chill in the air. It seems the Pine Grosbeaks go entirely by length of day to determine their migration patterns.