Complex sentence: It was one of the first sites to be made a World Heritage Site by UNESCO (1978); however, due to serious population declines of the characteristic native species, in 1996 it was also added to the List of World Heritage Sites in danger.
Split into simpler sentences: It was one of the first sites to be made a World Heritage Site by UNESCO (1978). However, due to serious population declines of the characteristic native species, in 1996 it was also added to the List of World Heritage Sites in danger.