Learn French: Le singe intriguant la femelle est jeune. - The monkey intriguing the female is young.

In French, verbs ending in -guer like intriguer drop the 'u' when they become verbal adjectives (intrigant), but keep the 'u' when used as present participles (intriguant). Because the word is acting as an active verb in this sentence, it is the present participle and keeps the 'u'.

How can I tell for sure that intriguant is a present participle and not a verbal adjective in this sentence?

The biggest clue is that it takes a direct object (la femelle). Verbal adjectives act like regular adjectives to describe a noun's static state or quality, whereas present participles express an action happening in the moment and can act on objects.

Could I rephrase this sentence using qui instead of the present participle?

Yes! You can almost always replace an active present participle with a relative clause. This sentence means the exact same thing as Le singe qui intrigue la femelle est jeune.

Is femelle the standard word for 'female' in French?

Yes, but strictly for animals! You use femelle for female animals and mâle for males. Using femelle as a noun to refer to a human woman is highly pejorative in French, so you must stick to femme for people.