Jim, 

I think Eugenia is right that the 'le' in this clause is replacing a repetition of the adjective 'adaptées' from the prior clause, as in French the adjective needs to (should) be 'repeated' in this 2nd clause. (In English we can either leave it out, or include it especially for emphasis). The grammar references attached to the translation support this also - the lesson on the neuter object pronoun 'le' to replace adjectives is included.

Eugenia is also correct that it is not obligatory to use 'le' in this way, and the alternative expression she has written would also be correct.

However, just as in English, French tries to avoid repeatedly expressing things in the same way, so using the neutral pronoun 'le' here for the adjective would be quite normal and common.

Using neuter pronoun le to replace adjectives (French Direct Object Pronouns)

Hi Eugenia,

"The cat's claws are well adapted for climbing up trees, but much less so for climbing back down"

So the "le" represents "doing it" that is climbing back down (as an action).

"They are less able (adaptable)to do IT when climbing down" (It = Direct object pronoun=le)

This as my understanding  --  hope it helps.

Jim