Complex sentence: On 22 May 2006 it was announced that a pair of white-tailed eagles breeding in the Oostvaardersplassen nature reserve in the Netherlands had arrived on their own, not as a reintroduction.
Split into simpler sentences: On 22 May 2006 it was announced that a pair of white-tailed eagles was breeding in the Oostvaardersplassen nature reserve in the Netherlands. They arrived on their own, not as a reintroduction.