The ice was not drifting fast enough to be noticeable, although by late November the speed was up to seven miles (11 km) a day. By 5 December, they had passed 68°S, but the direction was turning slightly east of north. This was taking them to a position from which it would be difficult to reach Snow Hill Island, although Paulet Island, further north, remained a possibility. It was about 250 miles (400 km) away, and Shackleton was anxious to reduce the length of the lifeboat journey that would be necessary to reach it. Therefore, on 21 December he announced a second march, to begin on 23 December.Conditions, however, had not improved since the earlier attempt. Temperatures had risen and it was uncomfortably warm, with men sinking to their knees in soft snow as they struggled to haul the boats through the pressure ridges. On 27 December, carpenter Harry McNish rebelled and refused to work. He argued that Admiralty law had lapsed since Endurance's sinking, and that he was no longer under orders. Shackleton's firm remonstrance finally brought the carpenter to heel, but the incident was never forgotten. Two days later, with only seven and a half miles' (12 km) progress achieved in seven back-breaking days, Shackleton called a halt, observing: "It would take us over three hundred days to reach the land". The crew put up their tents and settled into what Shackleton called "Patience Camp", which would be their home for more than three months.Supplies were now running low. Hurley and Macklin were sent back to Ocean Camp to recover food that had been left there to lighten the sledging teams’ burden. On 2 February 1916, Shackleton sent a larger party back, to recover the third lifeboat. Food shortages became acute as the weeks passed, and seal meat, which had added variety to their diet, now became a staple as Shackleton attempted to conserve the remaining packaged rations. In January, all but two teams of the dogs (whose overall numbers had been depleted by mishaps and illness in the preceding months) were shot on Shackleton's orders, because the dogs' requirements for seal meat were excessive. The final two teams were shot on 2 April, by which time their meat was a welcome addition to the rations. Meanwhile, the rate of drift became erratic; after being held at around 67° for several weeks, at the end of January there was a series of rapid north-eastward movements which, by 17 March, brought Patience Camp to the latitude of Paulet Island, but 60 miles (97 km) to its east. "It might have been six hundred for all the chance we had of reaching it across the broken sea-ice", Shackleton recorded.The party now had land more or less continuously in sight. The peak of Mount Haddington on James Ross Island remained in view as the party drifted slowly by. They were too far north for Snow Hill or Paulet Island to be accessible, and Shackleton's chief hopes were now fixed on two remaining small islands at the northern extremity of Graham Land. These were Clarence and Elephant Island, around 100 miles (160 km) due north of their position on 25 March. He then decided Deception Island might be a better target destination. This lay far to the west, toward the South Shetland Islands, but Shackleton thought it might be attainable by island-hopping. Its advantage was that it was sometimes visited by whalers, and might contain provisions, whereas Clarence Island and Elephant Island were desolate and unvisited. To reach any of these destinations would require a perilous journey in the lifeboats, once the floe upon which they were drifting finally broke up. Earlier, the lifeboats had been named after the expedition's three chief financial sponsors: James Caird, Dudley Docker and Stancomb Wills.

Question: What animal's meat was added to their diet on April 2?
Answer: dogs