The Journal of Brief Ideas

By Edward Christien Michael Parsons

The females of many animals may assess the fitness and health of males via displays or physical features, such as the tail of a peacock [http://en.wikipedia.org/wiki/Signalling_theory]. Physical features may be a “handicap” that fit males can overcome. Male killer whales have large (2m), straight dorsal fins that project perpendicularly from their backs whereas females and juveniles have smaller, curved hydrodynamic fins. The large, straight-edged fin of the male would produce substantive drag and would presumably be a handicap. Are the large dimorphic fins of male killer whales a secondary sexual characteristic, via which females can visually assess male fitness? Dorsal fins are comprised of connective tissue, and bent or collapsed male killer whales fins are rare in the wild. The percentage of male killer whales with collapsed fins ranges from 1%-5% in British Columbia [http://www.amazon.com/Killer-Whales-Genealogy-Columbia-Washington/dp/0774804696/ref=sr_1_fkmr0_1?ie=UTF8&qid=1430411496&sr=8-1-fkmr0&keywords=ford+%26+killer+whales+%26+1994]. Injury or poor health has been associated with collapsed fins [http://www.nmfs.noaa.gov/pr/interactions/injury/pdfs/day2_1155_baird_gorgone.pdf]: 2 of 3 animals reported in Alaska with collapsed fins had been exposed to the Exxon Valdez oil spill [http://www.amazon.com/Killer-Whales-Southern-Alaska-Matkin/dp/0963346792/ref=sr_1_fkmr0_1?ie=UTF8&qid=1430411410&sr=8-1-fkmr0&keywords=Matkin%2C+C.O.%2C+Ellis%2C+G.M.%2C+Saulitis%2C+E.L.%2C+Barrett-Lennard%2C+L.G.%2C+Matkin%2C+D.R.+1999.+Killer+whales+of+southern+Alaska.+North+Gulf+Oceanic+Society%2C+Homer%2C+Alaska.+96+pp.]; in New Zealand, 23% of males in one population had misshapen dorsal fins, but only one of these, who had suffered an injury as the result of entanglement, had a completely collapsed fin [http://www.aquaticmammalsjournal.org/share/AquaticMammalsIssueArchives/1998/AquaticMammals_24-02/24-02_Visser.pdf].