Read the passage given below and answer the questions (91 - 99 ) that follow :

Pelicans are birds. There are more than half a dozen species of pelicans. All of them have the sack for which the birds are best known all over the world. The sack is like a big bag of skin hanging under their bill, or their mouth. These large carnivorous birds use them to catch fish. Many pelicans fish by swimming in a group. They may form a line or a “U” shape and drive fish into shallow water by beating their wings on the surface. When the fish collect in the shallows, the pelicans simply scoop them up. The brown pelican, on the other hand, dives on the fish from above and traps them in its bill. Pelicans do not store fish in their pouch, but simply use it to catch them and then tip it back to drain out water and swallow the fish immediately. The American white pelican can hold some 11.5 litres of water in its bill. Young pelicans feed by sticking their bills into their parents’ throats to retrieve food.

Along with giant pouch, pelicans are large birds with short legs, and they appear rather clumsy on land. Once in water, they are strong swimmers, thanks to their webbed feet. This means that webbing connects all four of their toes, even the back toe.

Pelicans are found on many of the world’s coastlines and also along lakes and rivers. They travel in flocks. They also breed in groups called colonies, which typically gather on islands. The average life span of pelicans in the wild is about 10 to 25 years and their average body size is about 1.8 metres but when they open their wings their wingspan is around 3 metres. These large birds usually weigh around 13 kg.

Identify the clause in the underlined part of the sentence.

When the fish collect in the shallows, the pelicans simply scoop them up.