The study, published in the Proceedings of the Royal Society on Wednesday, says the animals did well in the 1980s but found the going tougher as demand for krill began to draw level with supply in the 1990s. The research has implications for the management of krill stocks, Mr Reid told BBC News Online. Some species will find alternatives when they fail to get enough krill.
Macaroni penguins take other small crustaceans and they seem to maintain their breeding success.
Gentoo penguins sometimes have a bit more difficulty. It is believed that krill stocks are affected by the slow but steady rise in air temperature over the Antarctic Peninsula during the last 50 years but it is very difficult to work out whether the changes are due to natural cycles or human activity. It might be that that in itself is just a long cyclical process. But for those who have to work out how best to conserve krill stocks, the cause of the changes may not matter. Recipients should seek permission to reprint the article from the source listed above.