Tale of the Tail
The Ibizan's tail is more than a cosmetic component. It must be set rather low and long enough to reach well below the hocks. It was said in the Balearics that a dog in condition should have a tail that can be pulled between the hind legs and up over the back to reach the spine. This statement says two things, that the length of the tail is correct and that the Ibizan is in hunting condition. The tail can be carried in many positions; there is a certain prejudice against curlier tails in Spain. I believe this was somewhat arbitrary decision from certain breeders at the time that the standard was written. You can get that impression from the letter fragment as the Marguessa de Belgida describes the proper Ibizan tail. The Marguessa was a breeder in Spain that was a mentor to fanciers early at the introduction of the Ibizan to the United States.
Certainly the Ibizan comes by any curl naturally as its Egyptian ancestors had very curly tails.
From observation I would say about 1/3 of Ibizans have remarkably curly tails.
The tail acts as a rudder when in motion. But most importantly, it is a beacon and a flag when the dog is hunting. When the Ibizan is closing in on its quarry, the tail becomes extremely animated. Traditionally the Ibizan is hunted in rough brushy terran. I believe this has helped shaped the breed. A tail must be carried high at this time to inform the person with dogs of the process of the hunt. A tail carried too low or curled very tightly would not be so informative to the hunter.
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Most Ibizans allow their tail to hang when standing relaxed. There is longer hair along the underside of the tail, some more, some less. This should not be trimmed.
Personally I prefer an Ibizan Hound that carries its tail up rather than out behind. This prevents the Tail from being caught in doors or sweeping the coffee table clean. But no matter how the Ibizan carries it's tail it is often wagging.