One of the best known humpback behaviors is singing, although the animals have no vocal cords and the way they produce the sound is still being studied. The performance is done by the males while they are suspended with their head down. The songs will vary from year to year and in different regions, but all males in an area will sing the same song, which can last for 20 minutes to over an hour and possibly be heard hundreds or even thousands of miles away. Some baleen whales will skim the water for food as they swim, but humpbacks feed by lunging at large concentrations of prey. Most fish will not swim through air bubbles, so the humpbacks will circle around below krill or fish and blow bubbles under them, corralling them, an activity that is often a cooperation between many members of a pod. Breaching and spy hopping are two activities that the whales are known for above the surface. They breach by rocketing towards the surface and then falling back in with a mighty splash. This may help to remove parasites from the animal or it may just be a social activity. Spy hopping is when they surface straight up until their flippers are exposed and survey the area. They can dive to 700 feet and remain submerged for 30 minutes. While those numbers seem impressive, the record holder is the Cuvier’s beaked whale with a submersion record of two hours and a depth of two miles, which is about 9000 feet deeper. However, humpbacks are listed in the Guinness World Records as having the longest migration of any mammal – 5095 miles.