Siskis are tiny, bright-eyed, highly intelligent creatures found in Mid Wood, in Topaz territory. Due to their small size, they easily become prey to the Wenn, and are therefore going extinct.
Secrets of Deltora
Doran described Siskis as bright-eyed, highly intelligent creatures found in Mid Wood, in Topaz territory. With the rise of the Flesh Python population, due to the extinction of Topaz dragons, Siskis were quickly becoming endangered. 
Siskis make their habitat in Mid Wood of The Forests of Silence. They can only be found there.
Not much is known about the appearance of a Siskis, other than that they are described as tiny, bright-eyed, furred creatures with dexterous paws. When angry, Siskis have the ability to puff up their fur to make themselves appear larger and fiercer.
Siskis have a drastically different apeprance in the anime. They are portrayed as balls of fur with no visible mouth or paws, a fluffy tail, and long strands of fur coming from the top of their heads.