Complex sentence: The leverets (young hares) are fully furred and are precocial, being ready to leave the nest as soon as they are born, an adaption to the lack of physical protection relative to that afforded by a burrow.
Split into simpler sentences: The leverets (young hares) are fully furred and are precocial, being ready to leave the nest as soon as they are born. Thus hares are adapted to the lack of physical protection, relative to that afforded by a burrow.