sentence: Different authorities recognise between two and eight species.
sentences_before: They are similar in size but slightly smaller than the Herring Gull.
sentences_after: This group has a ring distribution around the northern hemisphere. Differences between adjacent forms in this ring are fairly small, but by the time the circuit is completed, the end members, Herring Gull and Lesser Black-backed Gull, are clearly different species.
concept_name: different authority
headings: Lesser Black-backed Gull
categories: Charadriiformes