The camouflaging stripes of woodland living ungulates like bongos and bushbucks are much less vivid with less contrast with the background colour. In addition, unlike tiger stripes, the spatial frequencies of zebra stripes do not line up with their environment. A 2014 study of wild equines could not find any correlations between striping patterns and woodland habitats. Zebras being less noticeable at night than other prey animals is not supported by modern experiments. The confusion hypothesis states that the stripes confuse predators, be it by: making it harder to distinguish individuals in a group as well as determining the number of zebras in a group; making it difficult to determine an individual's outline when the group runs away; reducing a predator's ability to keep track of a target during a chase; dazzling an assailant so they have difficulty making contact; or making it difficult for a predator to deduce the zebra's size, speed and direction via motion dazzle. This theory has been proposed by several biologists since at least the 1970s. A 2014 computer study of zebra stripes found that they may create a wagon-wheel effect and/or barber pole illusion when in motion. The researchers concluded that this could be used against mammalian predators or biting flies. The use of the stripes for confusing mammalian predators has been questioned. The stripes of zebras could make groups seem smaller, and thus more likely to be attacked. Zebras also tend to scatter when fleeing from attackers and thus the stripes could not break up an individual's outline. Lions, in particular, appear to have no difficulty targeting and catching zebras when they get close and take them by ambush. In addition, no correlations have been found between the amount of stripes and populations of mammal predators. Hughes and colleagues (2021) concluded that solidly grey and less contrasted patterns are more likely to escape being caught when in motion. The aposematic hypothesis suggests that the stripes serve as warning colouration. This hypothesis was first suggested by Wallace in 1867 and discussed in more detail by Edward Bagnall Poulton in 1890. As with known aposematic mammals, zebras are recognisable up close, live in more open environments, have a high risk of predation and do not hide or act inconspicuous. However they are frequently preyed on by lions, suggesting that stripes do not work on them but may on smaller predators, and are not slow-moving enough