Northern rockhopper penguin colonies in a range of locations from sea level or on cliff sides, to sometimes inland. The Northern form, found in Amsterdam and Gough island, is reproductively isolated from the Crozet and Kerguelen islands. They are monophyletic; meaning they have a split in the mitochondria DNA trees which forms two subspecies: the northern and southern rockhopper penguin. Another interesting difference between the two subspecies is their mating ritual. They both use different songs and head ornaments in their mating signals. The reproductive isolation has led to not only physical difference but also behavioral. The adults feed their chicks lower trophic
Rockhopper Exploration in production licences PL023, PL024, PL032 and PL033 covering approximately 3800 km. In 2005 it farmed into licences PL003 and PL004 operated by Desire Petroleum plc. In 2011, Rockhopper increased its share of PL004b from 7.5% to 60.0% and in PL004c from 7.5% to 25.0%. Licence PL004b contains an extension to the Sea Lion field as well as the Beverley, Casper and Casper South discoveries. The Rockhopper board comprises eight directors; a non-executive chairman, three executive directors and four non-executive directors, one of whom acts as senior independent director. Four of the non-executive directors are considered to be independent. The