Jizz

Jizz, the general impression of size and shape, is birding slang for how to ID a dark smudge in the scope's field of view.

Imagine seeing a black dot in your binoculars somewhere in this maze. 

Then you put the scope on it.

And see a blob with wings, like this. 

How is it possible to ID a bird that far away? 

The people I work with are real raptor biologists. I've spent days shadowing some of them, and they all use tiny clues to ID birds at distance, sometimes, up to seven kilometers away. 

Split-second impressions used to form the jizz:

1. shape
2. posture
3. flying style
4. habitual movements
5. coloration
6. voice
7. habitat
8. location

For example: 

Sharp-shinned Hawks (SSHA) and Cooper's Hawks (COHA) are some of the hardest raptors to tell apart. About the same size and shape, both are supreme aerialists. 

But there are small differences. SSHA have more play in the wrists than COHA. Also, they are more compact. Heads so small, that at a distance they can look headless, like a flying mallet: the wings are the head of the mallet and the tail the handle. 

Sharp-shinned Hawk - photo by Tim Lenz

COHA have a longer tail and more head projection. 

Cooper's Hawk - photo by John Williams

COHA fly stiffer than SSHA and with a straight leading edge. 

When one of these good biologists says, "It's jizzing like a Sharpie," they aren't being dirty.