Antarctic seabirds are breeding（繁殖）later, because thinner sea ice is causing their food supplies to decline, a new study says. The birds, which nest in East Antarctica, have delayed their spring arrival by an average of nine days and egg-laying by an average of two days over the past 50 years, according to polar researchers from the French National Center for Scientific Research in Villiers en Bois, France, study authors Christophe Barbrand and Henri Weimerskirch attribute this later breeding activity to decreases in sea ice caused by climate change.

The researchers say the disappearing sea ice, combined with a longer sea-ice season, has interfered with the birds’ breeding cycle by reducing the amount of krill（磷虾） and other prey（猎物）available in early spring in Antarctica. Because Antarctica’s seasons are opposite those in the Northern Hemisphere, spring on the icy continent begins in October.

The study is based on data collected at seabird colonies between 1950 and 2004 in Adélie Land, on the eastern edge of the frozen continent.

The findings were published in the journal Proceedings of the National Academy of Sciences.

Of the nine species studied, some arrived up to 30 days later than they had in previous years.

Despite much later arrivals, the birds are laying their eggs at pretty much the same time as they had in the past. In the most extreme cases, birds were laying their eggs an average of 3. 7 days later in the season than they were 50 years ago.

56. What is the passage mainly about?

A. Seabirds are breeding later in East Antarctica.

B. The amount of krill in the ocean has decreased.

C. The weather in Antarctica has changed.

D. The spring in Antarctica is beginning later.

57. Why have the seabirds in East Antarctica delayed their breeding?

A. The food there has been polluted.

B. The sea ice doesn’t shrink any more.

C. The food supplies there have declined.

D. There are too many seabirds there.

58. In which of the following months is it autumn in Antarctica?

A. October.                                                     B. September.

C. November.                                                  D. June.

59. How many kinds of seabirds were studied by the researchers?

A. Two.                B. Five.                             C. Nine.                       D. Thirty.

60. What does the underlined word “attribute”in Para. 1 mean?

A. contribute                                                    B. cause

C. owe                                                                   D. devote