Well, that is something I haven’t thought about in a while. Until we get clarification otherwise I’m going to assume the answer is ‘not enough to really matter’. Although the biologist in me thinks “Wow, that would be cool!” The game designer in me is saying, “this would be very likely to be used inappropriately to the detriment of the experience.” [Although, I might look into using this for home game flavor amongst mature players.]
What I have seen more of is different male/female behavioral traits that players create. A friend had a tengu that swaggered about, unconsciously preening for an audience. He placed white and red feathers amongst his black, and had the amazing dexterity based combat prowess [presumably to mimic bird sexual displays].
The main thing is that his personality was not just that of a “male bird” but also a creature with human-level intelligence and personality. He displayed unusually dry wit, and when given the opportunity would defend his companions to the last. He had the character flaw of being quick to anger (undesirable but still human). What I really love is when humanoids display depth of character. I feel like Pathfinder hands us these opportunities all the time if we’d all merely step outside of ourselves and take them.
How I have seen humanoids (and specifically tengu) played before in other communities, leads me to a more pessimistic point of view on the whole thing. To some individuals humanoids such as tengu, nagaji, and grippli are a template for attention seeking. Not a resource to explore the human condition, or to adventure as.
[Stay on target! Stay on target!]
In other words, I don’t see a lot of hallmark traits of sexual dimorphism being referenced in the materials or art. This doesn’t mean there isn’t any, but perhaps not the kind most people are familiar with. Perhaps there are physiological, psychological or behavioral differences instead. Perhaps, we should brainstorm some?
[Hmm, I'll have to read some of Mercedes Lackey's writings now... she has a lot of experience with bird behavior...]