Using "who" to describe animals isn't only seen in literary classics. For their study, Gilquin and Jacobs compared the policies for the usage in dictionaries, encyclopedias, grammars, publication manuals, newspapers and news agencies. Of these, they found that it was deemed acceptable to use "who" to describe an animal in 20 of the 45 sources -- almost half. There are lots of nuances, though -- for instance, the Associated Press Stylebook, used by many news publications (including The Dodo) says use use the pronoun "who" for "references to human beings and to animals with a name."
Other noted publications that allow for the use of the pronoun "who" to refer to animals include the New York Times, the Los Angeles Times, The Independent, the Chicago Tribune, the Dallas Morning News, the Washington Post, the Wall Street Journal, the Oxford Guide to English Grammar, the Oxford English Dictionary, Merriam-Webster's dictionary, the American Heritage Dictionary, among others (though many of these include limitations on whether "who" can be used, like knowledge of the animal's name or gender).
Publications that do not allow for the pronoun "who" to be used in describing an animal include the Times of London, Reuters, the Houston Chronicle, the American Psychological Society's manual, the Chicago Manual of Style, Parrot's Grammar for English Language Teachers, Cambridge Advanced Learners' Dictionary and Encarta, among others.
The researchers also examined the British National Corpus World Edition, a 100-million-word collection of spoken and written materials, to see how frequently the word was actually used to describe animals in the real world. The researchers found 738 sentences in which the usage is found, a frequency of .76 per 100,00 words. Although not a frequent phenomenon, the usage is certainly popular, they wrote.
"I was pleasantly surprised to see so many uses of ‘who' with animals and so many reference works and style guides saying that it is okay," said Jacobs.
Interestingly, there were certain factors that made speakers and writers more likely to use "who" rather than "which" -- one of those was the type of animal involved. They ranked the animals in order of how often they occurred in the research: