Meaning of Jizz

From Birdchick Blog

Speaking of which, I've heard Pete Dunne is coming out with his own field guide and I've heard that he's going out and watching birds and then going to describe the birds individually based on his personal experiences with the birds and their "jizz" (Note to all of us under 40--jizz in birding terms doesn't mean what we thought it meant in high school. In birding terms it means the over all feel of the bird, so quit your snickering when you hear a 73 year old birder say, "Well, the jizz of that bird makes me say loggerhead shrike.") Anyway, kind of goes back to that theory of looking at birds by shape and behavior as opposed to just color.

As well, Identification by Behaviour from WildBirds.com describes jizz and how, when one gets to know it for bird or family of birds, it makes identification from glimpses of a bird possible.