A rabbit's ears contain an intricate system of blood vessels, which allow the rabbit to release heat through its ears, helping regulate its body temperature. Rabbits overheat easily in warm weather, so if your bunny's ears feel hot to the touch, you should carefully monitor your rabbit for signs of overheating. On the other hand, very hot ears may be a sign of an ear infection or infestation.
The Outer Ear
The visible, outer ear is called the "pinna," which, according to Jana Rickel of Sound Diagnostics, may account for up to 12 percent of the rabbit's total surface area. The pinna has an extensive network of blood vessels providing a great deal of surface area for heat exchange. When the rabbit overheats, the ear vessels swell with blood. As blood circulates through the ear, heat is released, so blood returning to the body is cooler than when it entered. The outer ear is where ear mite infestations occur, as well as wax buildup and infection, which may hinder the release of heat from the ears.
The Inner Ear
The middle ear is where hearing occurs, and consists of an air-filled cavity and the eardrum. Three small bones called ossicles transfer the pressure of a sound wave from the eardrum to the inner ear. The inner ear receives sound and also keeps track of the body's movement and position. The inner ear connects to the rest of the respiratory system. Hot ears on a cool day could indicate that the rabbit has an inner ear infection or a fever.
A rabbit's ears being hot may simply mean the ears are doing their job of releasing body heat. However, hot ears accompanied by lethargy, heavy breathing or anorexia may indicate that the rabbit is overheating. According to the House Rabbit Society, misting a rabbit's ears with cool water can help cool an overheated bunny. Or, wipe the bunny's ears with a damp, cool cloth.
Ear mites are more common in outdoor rabbits than bunnies that live inside. These tiny parasites create a scabby, brown crust that covers the rabbit's outer ears and may inhibit the release of heat from the bunny's ears. Luckily, ear mites are easily treated and prevented by a dose of Advantage (imidacloprid) or Revolution (selamectin).
Hot ears accompanied by head-shaking and ear-scratching may be a sign of an infection in the inner or outer ear. A veterinarian can determine the best antibiotic to eliminate the infection. Middle and inner-ear infections may require long-term antibiotics. Ear infections left untreated often spread to the respiratory system and may result in "headtilt," a condition in which a rabbit rolls its head or cannot hold its head up.