Learn French: Les jeunes mâles sont souvent négligents. - The young males are often neglectful.

This is the core difference between this verbal adjective and its corresponding present participle! The present participle of the verb négliger is négligeant (it needs the e after the g to keep the soft sound before the a). However, the verbal adjective changes its spelling to end in -ent, becoming négligent.

Why is there an s at the end of négligents?

Because it is functioning as a verbal adjective, it must agree in gender and number with the noun it describes (Les jeunes mâles, which is masculine plural). If this were a present participle expressing an action, it would be invariable and never take an s.

Is the word mâles used for humans or just animals?

It is primarily used for animals. While it can be applied to humans, it sounds very clinical, biological, or sometimes derogatory, much like using the word 'males' to refer to men or boys in everyday English.

Why is souvent placed after sont rather than at the end of the sentence?

In French, short adverbs of frequency like souvent (often), toujours (always), and jamais (never) naturally sit immediately after the conjugated verb.