Feral sheep and pig on Santa Cruz Island continue to be hunted as a game animal. The exact date of introduction of the animals is unknown but best estimates place it around the 1850s. There are approximately 3000 sheep and 1000 or more pig remaining on the island.

There are only four native terrestrial mammals which occur on the island: the Santa Cruz Island fox (Urocyon littoralis santacruzae), the spotted skunk (Spilogale gracilis amphialus), the deer mouse (Peromyscus maniculatus santacruzae), and the western harvest mouse (Reithrodontomys megalotis santacruzae).

There are 10 birds which are Channel Island subspecies or races. They include: Allen's hummingbird, western flycatcher, horned lark, Santa Cruz Island jay, Bewick's wren, loggerhead shrike, orange-crowned warbler, house finch, rufous-sided towhee and the Catalina quail (introduced). There are many other land and marine birds which make there home on the island.

Due to the large size, and topographic and geologic complexity of Santa Cruz Island, this island supports a wide variety of plant communities. Coastal strand, coastal bluffs, valley and foothill grasses, coastal sage scrub, chaparral, island and oak woodlands, pine forests, southern riparian woodlands, and marsh communities are all present. Introduced cultivated plants occur as well.

There are over 650 different plants on Santa Cruz Island, including both native and introduced species. Forty two of these plants are endemic to the Channel Islands and 9 are endemic to Santa Cruz Island in particular.