Complex sentence: Most of the introduced species have proved to be unequal to Bermuda's frequently fierce weather, and winter storms and a few powerful hurricanes that have struck over the last two decades have reduced woodlands, and available nest sites for small birds.
Split into simpler sentences: Most of the introduced species have proved to be unequal to Bermuda's frequently fierce weather. A succession of winter storms and a few powerful hurricanes that have struck over the last two decades have reduced woodlands, and available nest sites for small birds.