According to this article the number of penguins has halved in the 30 years. The problem is that climate change has been responsible for a decline in the the number of krill, the penguins main source of food. The huge reduction in numbers of the penguins main prey appears to be having a direct affect on the numbers of penguins. Krill density has dropped by as much as 80% due to rising temperatures and increased competition from marine mammals. It was previously thought that melting sea ice was behind the decline in the penguin populations, however, the new evidence reported in the journal Proceedings of the National Academy of Sciences suggests it is mainly due to krill loss.