Complex sentence: They breed colonially from September onwards, making raised cup nests out of organic material and guanoCon islands and sea cliffs.olonies are large enough to be strikingly visible, and are used year after year.
Split into simpler sentences: They breed colonially from September onwards, making raised cup nests out of organic material and guano on islands and sea cliffs. Colonies are large enough to be strikingly visible, and are used year after year.