Between the 1940s and the 1980s the population of rockhopper penguins breeding on New Zealand’s Campbell Island decreased by about 94%. Drastic declines have been reported throughout much of the species’ circumpolar subantarctic range. The cause is unknown, but one reason could be the increasing sea-surface temperatures since the Second World War, causing changes to the availability of their prey. Could rockhopper penguins be the harbingers of global warming? Some scientists think so.
|Eastern Rockhopper (source)|
Hmmmm.....another outcome from man-made global warming?
Or perhaps the cause of the decline was caused by land slips as recorded by the New Zealand Government Conservation Blog:
The survey also monitored what effect recent slips have had on the penguin populations. Initial observations had suggested that up to one fifth of the colony had been affected by these natural slips.The 2015 population count headed by Jo Hiscock, Senior Biodiversity Ranger found the penguin population on the subantarctic Antipodes Islands, found no change from the 2011 survey:
The survey results for the eastern rockhopper penguin showed that there was no change from the 2011 count.
A recent paper in Polar Biology by Morrison et al (link)