The Castaways of the Flag by Jules Verne

It took Mrs. Wolston some time to recover from her terrible shock. But Bob was restored to her, and that comforted her.

It appeared that Bob, playing with the albatross, had followed it to the back of the cave. The bird made its way in through the narrow passage, and Bob went after it. A dark excavation opened out at the end, and when the little fellow wanted to get out of this he found that he could not. At first he called, but his calls were not heard. Then he lost consciousness, and nobody knows what might have happened if by the luckiest chance Fritz had not happened to hear the cry of the albatross.