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Flashy colors may throw off predators, study finds

Aug. 13, 2008
Special to World Science  

Re­search­ers say they fi­nally have ev­i­dence for some­thing bi­ol­o­gists had long sus­pected: cam­ou­flage is­n’t the only type of col­ora­t­ion prey an­i­mals can use to throw off preda­tors. Sur­pris­ing­ly, flashy col­ors may al­so do the trick.

Colorful fish at Rap­ture Reef, Ha­waii. (Cour­tesy NOAA/James Watt)
The “daz­zle mark­ings” and high-contrast pat­terns on some an­i­mals, such as ze­bras, are thought to con­fuse preda­tors by mak­ing it harder to es­ti­mate the speed and di­rec­tion of the prey. 

In some cases, it’s the­o­rized that the mark­ings make an ob­jec­t’s true out­line hard to dis­cern, or cre­ate il­lu­sions that in­ter­fere with the brain’s mo­tion de­tec­tion mech­a­nisms.

Based on si­m­i­lar rea­son­ing, some Brit­ish ships in World War I wore “daz­zle paint­ing” to evade Ger­man sub­ma­rine at­tacks. The idea was that since cam­ou­flage does­n’t work well on ships, the best al­ter­na­tive would be the op­po­site ex­treme.

But no study has been able to prove that “daz­zle col­ora­t­ion” really works, ac­cord­ing to the au­thors of the new stu­dy, Mar­tin Ste­vens of the Uni­ver­s­ity of Cam­bridge and col­leagues. The dif­fi­cul­ty in stu­dying the is­sue is partly be­cause of eth­i­cal ques­tions in­volved in set­ting up ex­pe­ri­ments in which preda­tors chase down prey.

Ste­vens and his col­la­bo­ra­tors worked around the is­sue by de­vel­op­ing a com­put­er game where hu­man play­ers, as “preda­tors,” had to cap­ture com­put­er-generated prey mov­ing across a back­ground. The re­sults: “although un­iform cam­ou­flaged tar­gets were among the hard­est to cap­ture, so were a range of high-contrast con­spic­u­ous pat­terns, such as bands and zigza­gs,” the re­search­ers wrote. 

The find­ings ap­peared on­line Aug. 12 in the re­search jour­nal Bi­o­log­i­cal Sci­ences. “Some an­i­mals may com­bine such daz­zle pat­terns with oth­er func­tions, such as cam­ou­flage, ther­moregula­t­ion [tem­per­a­ture con­trol], sex­u­al and warn­ing sig­nals,” Ste­vens and col­leagues added.

The re­search­ers con­ced­ed that the use of the hu­man play­ers—72 in one ex­pe­ri­ment, 50 in anoth­er—could dis­tort the re­sults be­cause of dif­fer­ences be­tween hu­mans and an­i­mal per­cep­tion. On the oth­er hand, ex­pe­ri­ments with an­i­mals could al­so suf­fer a host of “con­found­ing fac­tors” that would lead to un­clear re­sults, such as varia­t­ions in the prey an­i­mals’ be­hav­ior, they ar­gued. 

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Researchers say they finally have evidence for something biologists had long suspected: camouflage isn’t the only type of coloration prey animals can use to throw off predators. Surprisingly, flashy colors may also do the trick. The “dazzle markings” and high-contrast patterns on some animals, such as zebras, are thought to confuse predators by making it harder to estimate the speed and direction of the prey. In some cases, it’s theorized that the markings make an object’s true outline hard to discern, or create illusions that interfere brain’s motion detection mechanisms. Based on similar reasoning, some British ships in World War I wore “dazzle painting” to evade German submarine attacks. The idea was that since camouflage doesn’t work with ships, the best alternative is the opposite extreme. But no study has been able to prove that “dazzle coloration” really works, according to the authors of the new study, Martin Stevens of the University of Cambridge and colleagues. The difficulty in studying the issue is partly because of ethical questions involved in setting up experiments in which predators chase down prey. Stevens and his collaborators worked around the issue by developing a computer game where human players, as “predators,” had to capture computer-generated prey moving across a background. The results: “although uniform camouflaged targets were among the hardest to capture, so were a range of high-contrast conspicuous patterns, such as bands and zigzags,” the researchers wrote. The findings appeared online Aug. 12 in the research journal Biological Sciences. “Prey were also more difficult to capture against more heterogeneous than uniform backgrounds, and at faster speeds of movement,” Stevens and colleagues wrote. “Some animals may combine such dazzle patterns with other functions, such as camouflage, thermoregulation [temperature control], sexual and warning signals.” The researchers conceded that the use of the hapharzardly chosen human players—72 in one experiment, 50 in another—could distort the results because of differences between humans and animal perception. On the other hand, experiments with animals could also suffer a host of “confounding factors” that would lead to unclear results, such as variations in the prey animals’ behavior, they argued.