Complex sentence: Studies have now shown that by the 1970s four fifths of the ducks diet was made up of Baltic clams, which are very common in the Chesapeake Bay: the ducks have been able to adapt to the decline in SAV by changing their diet.
Split into simpler sentences: Studies have now shown that by the 1970s four fifths of the ducks diet was made up of Baltic clams, which are very common in the Chesapeake Bay. The ducks have been able to adapt to the decline in SAV by changing their diet.