The Rusty Blackbird is a medium-sized blackbird and is also a migrant through western Pennsylvania. I didn't know much about this species but after watching a small flock of them catching bugs in a swamp one morning, I decided to research the different markings that I saw. On the Cornell Lab of Ornithology website I found the reason for the distinct differences.
First, the breeding male is dark glossy black with a greenish sheen and yellow eyes.
Rusty BlackbirdBreeding Male
Second, the non-breeding male is dark brown overall with rusty edges of feathers, and a pale eye and eyebrow.
Rusty BlackbirdNon-breeding Male
Last but not least, the female is brownish to rusty colored with pale yellow eyes and dark feathers around the eyes.
Thanks for looking,