From classical and country to dub step and smooth jazz, humans have some drastically different opinions on music. But when it comes to animals, it seems that birds of a feather tend to rock together—or at least they tend to agree on what they hate. We know that because researchers in the UK recently exposed African grey parrots to folk, rock, pop, classical and techno. While some of the birds seemed relaxed while listening to classical music, others preferred to bob their heads to folk or rock music. The one thing they all agreed on was techno. Whenever the Chemical Brothers or Prodigy were played, the birds started acting stressed, screeching and squawking until the music was shut off.
Horses, too, are quite critical when it comes to their musical tastes. Another team of British researchers recently studied how horses behaved while exposed to classical, rock, country, and jazz (unfortunately, no techno was played). Strikingly, the horses were much bigger music critics than the parrots, showing stressed behaviors such as head tossing, stamping and snorting when both rock and jazz were played—seeming the most agitated by jazz (the researchers think it's because of jazz's fast tempo and minor key). On the other hand, when country and classical were played, the horses were far calmer than they were when no music was played at all.
Though the parrots and horses seemed to disagree on many genres, they did both agree that classical music is relaxing. So until similar studies are performed on dogs, cats, chinchillas, hamsters, and any other pets you may have, you might want to stick with classical if you want to play some music for your non-human friends.