Intersex bird species include some wild duck and pigeon species, the white-throated sparrow and the zebra finch, which can produce individuals showing bilateral sexual dimorphism, when half of the body has female characteristics and the other half shows male characteristics. Sometimes, birds can show external male characteristics but behave like females, producing ovule-like sexual cells. This behavior can be linked to hormonal unbalance.
Lizards, snakes and other reptiles can also produce intersex individuals. The Mexican snake Pseudoficimia frontalis has female-like individuals featuring male organs, called hemipenis, and male-like individuals with female organs. Lizards of the genus Lacerta also produce intersex individuals, which often die young or even before hatching. Leopard geckos can produce females with male organs and hormonal levels.
In some deer species, antlers are a visible clue to detect morphs, individuals that are neither males or females. The white-tail deer can show individuals with the body size of a male, small testicles and short or absent antlers, which are generally infertile. This phenomenon can happen among other species, including elks, fallow and roe deers. Some species of kangaroos can also produce intersex individuals, which often show both sexes.
Fish species featuring individuals that are not males or female include smallmouth and largemouth bass. Found across North American rivers, these species show intersex individuals: males with female anatomy and female sex cells in their testes. Although some species of amphibians can naturally produce intersex individuals, the increasing appearance of intersex cricket frogs (Acris crepitans) is often related to environmental unbalance, including chemical contamination. As intersex individuals do not reproduce, this trend affects the survival of the species.