Sentence:  During late spring and early summer it becomes difficult to detect <WSD>Ruffs</WSD> in their breeding habitat. The males no longer visit the leks, and most have left the area. Some of the females may still be sitting on their eggs, invisible to casual passers-by. 
Meaning of the word marked with <WSD> tags:  "Philomachus pugnax" (syn. (ver=170921)), a gregarious, medium-sized wading bird of Eurasia; "specifically", a male of the species which develops a distinctive ruff of feathers and ear tufts during mating season (the female is called a (id=bird)).