Complex sentence: The species is also unusual in that other members of the pack including males may be left to guard the pups whilst the mother joins the hunting group; the requirement to leave adults behind to guard the pups may decrease hunting efficiency in smaller packs.
Split into simpler sentences: The species is also unusual in that some members of the pack, including males, may be left to guard the pups whilst the others, including the mothers, join the hunting group. The practice of leaving adults behind to guard the pups may decrease hunting efficiency in smaller packs.