That vs Which in plural contexts

Question

Almost all animals that hibernate prepare to do so by eating large amounts of food,which they convert to fat.

Among birds that forage in tree trunks, nuthatches are the only ones that regularly feed with their heads facing downward.

Why is the usage of 'that' in the following sentences correct. These involve plural sentences and shouldn't 'which' be used instead.

Also if there is any rule which differentiates the usage of 'that' for humans and animals, please do post that too.

PS : I've generally seen that used in singular sentences while those used in plural. Any examples involving the contrary would be deeply appreciated.

Answer 1

That is perfectly OK here. Grammatical number does not enter into the choice between that and which. Both of them (indeed, all English relative pronouns) may be used in both singular and plural contexts.

The only distinction between that and which/who/whom is that that is not permitted in non-restrictive bound relative clauses or as the object of prepositions:

John, that who had prepared better than the rest of us, came in first.
Put it back in the box from that which you took it.

That is rarely found at the head of fused relative clauses today; it is usually replaced by what. , When it is used there it should be understood as a demonstrative rather than a relative, and what follows it is a reduced relative clause with the relativizer deleted.

Your pain is trivial compared to that she suffered = that which she suffered

Some of the prissier stylists demand that only that be employed in restrictive relative clauses, but this has no justification in contemporary or historical practice.