Complex sentence: Cliff nesting for gulls occurs only in the "Rissa" species, and the Kittiwake is capable of utilizing the very sheerest of vertical cliffs, as is evident in their nesting sites on Staple Island in the outer Farne Islands (Hogan, 2005).
Split into simpler sentences: Cliff nesting for gulls occurs only in the "Rissa" species. Kittiwakes are capable of utilizing the very sheerest of vertical cliffs, as is evident in their nesting sites on Staple Island in the outer Farne Islands (Hogan, 2005).