Filter feeder gap between the two rows of baleen plates lets the water in together with the prey, while the baleens filter out the water. Rorquals such as the blue whale, in contrast, have smaller heads, are fast swimmers with short and broad baleen plates. To catch prey, they widely open their lower jaw — almost 90° — swim through a swarm gulping, while lowering their tongue so that the head's ventral grooves expand and vastly increase the amount of water taken in. Baleen whales typically eat krill in polar or subpolar waters during summers, but can also take schooling fish, especially
Baleen whale dense. Multiple species of baleen whale have been observed seeking out highly specific areas within the local environment in order to forage at the highest density prey aggregations. Baleen whales, primarily juveniles and calves, are preyed on by killer whales. It is thought that annual whale migration occurs to protect the calves from the killer whales. There have also been reports of a pod of killer whales attacking and killing an adult bowhead whale, by holding down its flippers, covering the blowhole, and ramming and biting until death. Generally, a mother and calf pair, when faced with the threat of