Learn Turkish: Kanıtladılar ki balinalar planktondan dolayı bu bölgeye dönüyor. - They proved that whales return to this region because of the plankton.

This is because of the word ki. While Turkish is normally a Subject-Object-Verb language, using ki to mean 'that' copies the Persian and English sentence structure. The main clause (Kanıtladılar) comes first, followed by ki, and then the full noun clause in its normal word order.

How would you say this sentence using native Turkish grammar instead of ki?

You would use the object participle -dik to turn the second clause into a direct object: Balinaların planktondan dolayı bu bölgeye döndüğünü kanıtladılar. Notice how the main verb (kanıtladılar) moves back to the very end of the sentence. Using ki is often preferred for long or complex clauses because it makes the information easier to digest.

Why do we use the ablative case in planktondan dolayı?

The postposition dolayı means 'due to' or 'because of,' and it strictly requires the word before it to take the ablative case (-dan/-den). While you could also use yüzünden ('because of'), dolayı sounds a bit more scientific and neutral, which fits perfectly with a sentence about proving a biological fact.

Why is the verb dönüyor in the present continuous tense if returning to the region is a general fact?