Very interesting! There's a common counter example of males usually larger in birds. It's often the males who are burdened by extra plumage to attract female mates; either the males appear bigger because of more feathers or they are bigger in order to have more muscle, etc. to move, fly, etc. with the extra plumage.

The exceptions are the birds of prey, who have to hunt and carry food all the time. The females, when nesting, are carrying eggs, which are a significant mass compared to the whole bird. In order to support that mass and still be swift, agile, and climb strongly to be able to hunt, the moms have to be larger; like, bigger wings to keep the wing loading in the same range and more muscle to move them.

Thanks for the post!