Big Bird Lays An Egg?

According to this Research Highlight at Nature.com, it seems that our favorite big yellow bird is more likely to be a lady-bird.J. Zool. doi:10.1111/j.1469-7998.2009.00596.x (2009)It seems that the constraints of egg shell strength conspire to limit how large a bird can be without crushing it's own eggs. Males of larger species tend to be smaller, and this may allow them to incubate their eggs