Sentence:  His birds are not carefully posed to illustrate every plumage detail; they are impressions rather than portraits. With a few deft strokes of his pencil, he captures their <WSD>'jizz</WSD>'. 
Meaning of the word marked with <WSD> tags:  The unique characteristics of a bird species that enable it to be immediately identified by an experienced birdwatcher who has seen that bird before and is familiar with its appearance and behaviour.