Branch lengths are scaled by dN rates. Branch lengths were estimated using a free ratio model as implemented in PAML, that estimates independent dN rates for each branch in the tree.
The common tern is a Holarctic colonially breeding and long-distance migratory seabird. One of its populations, located in the Banter See at Wilhelmshaven on the German North Sea coast (53.36N, 8.06S)
