Complex sentence: Due to the fact that these birds were extinct, not much is known about their life history.Unusal changes to low elevation ecosystems caused the downfall of many if not all major forest birds on Kaua`i.
Split into simpler sentences: Due to the fact that these birds were extinct, not much is known about their life history. Unusual changes to low elevation ecosystems caused the downfall of many if not all major forest birds on Kaua`i.