Complex sentence: The Mexican burrowing caecilian is listed as Vulnerable in the IUCN Red List of Threatened Species, because it is thought that numbers have declined by more than 30% over the last ten years.
Split into simpler sentences: The Mexican burrowing caecilian is listed as Vulnerable in the IUCN Red List of Threatened Species. This is because it is thought that numbers have declined by more than thirty percent over the last ten years.