According to a recent study from the Milner Centre for Evolution at the University of Bath, diving species like penguins, puffins, and cormorants may be more vulnerable to extinction than non-diving birds. The authors hypothesise that this is due to their extreme specialisation, which makes them less competent than other birds to adjust to shifting circumstances. Less than a third of the 727 species of water birds use diving as a method of food-seeking, making diving a relatively uncommon trait in birds. The study, published in Proceedings of the Royal Society B, found that diving evolved independently 14 times and that once a group had evolved the ability to dive, subsequent evolution didn’t reverse this trait. The researchers found that body size amongst the diving birds had evolved differently depending on the type of diving they did. Wing divers, such as penguins and puffins, use their wings to propel themselves through the water. These birds tend to have larger body sizes adapted for swimming. Birds that ‘foot dive’, such as cormorants, kick their feet to swim and are similarly larger in body size to the wing divers.