Homosexuality has been observed is just about every species it has been looked for. Transgender animals are not as widely known, but may just be a matter of looking for them.
There are certainly some animal examples that are various forms of transgender animals in nature. One is the California Sheephead (Semicossyphus pulcher) which is a fish that is born female, and then can become male later in life. Another example is found in the Green Frog (Rana clamitans) that reverse sex in response to various external factors, and this has been observed in other amphibians as well. But both of these examples are in lineages of animals that are pretty distantly related to us humans.
Photo of two lions one is male sex (left), one is female sex (right), but both display male characteristics.
Well, research published a couple of years ago in the African Journal of Ecology is an example much closer to us. In a paper by Gilfillan et al. from the University of Sussex, five lionesses in Botswana have been observed to grow manes, regularly roar and scent mark, mount other females, and display other very male-like behaviors such as killing the cubs of rival prides which females lions just about never do but is very common for male lions.
This is a mammal we are talking about.
Lions that are female in body, but male in behavior.
In the wild.
Still think being transgender is unnatural?
abirdingnaturalist 
animals don’t have gender identities. https://speakingofresearch.com/2021/04/14/factcheckneeded-non-human-animals-cannot-have-a-gender-identity/
Hi Lonny Byrd,
Firstly, homosexuality is commonly defined as “romantic attraction, sexual attraction, or sexual behavior between members of the same sex or gender.” This does not rely on gender identity. If an individual animal engages in sexual behavior with another individual of the same sex, that individual animal could rightly be identified as homosexual or bisexual (depending on the types of sexual interactions it engages in over the course of its life).
Secondly, I am not sure that you are correct that animals don’t have gender identities. To begin, let’s define the term. Gender identity is “each individual’s internal and individual experience of gender.” To say that no animal has this is a hugely broad statement. Are you really saying that NO animal (other than humans who are animals) have gender identities? That is a lot of animals! How can you be so sure that no other animal has an internal experience of gender? How do you know what is going on in the minds of so many other animals? Also, as we learn more and more about animal cognition and what does seem to be going on in their minds, we are learning that they are capable of a lot more than humans ever thought possible. It seems pretty reasonable to me that a chimpanzee or gorilla or a dolphin or a wolf or a lot of other species may have a sense of their own internal experience of gender.
Lastly, the link you sent seems to be broken, so I have no way to respond to whatever your source is.
You forgot to mention that the hormonal imbalances of these “trans” lions caused immense discomfort for the animals in question. A likely solution would be to introduce the correct chemicals to their bodies to right this wrong. And by citing animals that can physically alter their sex. That’s wholly different that the medical Frankenstein’s work humanity does. We cannot change sex as higher mammals period. It is a mental illness that needs to be treated with medication and therapy not chemical castration and mutilation.
Hi Nathaniel,
First off, I have a few questions about the your first few statements. 1) How do you know that the “trans” lions are uncomfortable? 2) What makes you say that these “trans” lions are wrongs that need to be righted at all? 3) I am not sure what “medical Frankenstein’s work” you are referring to. Would you care to provide some details?
In response to your last couple of sentences, namely: “We cannot change sex as higher mammals period. It is a mental illness that needs to be treated with medication and therapy not chemical castration and mutilation.”, I have several responses. For one thing, nowhere in my piece do I talk about humans changing the sex or gender of any animal, so I am not sure why you are bringing that up. For another, being trans is NOT a mental illness in humans, and I see no evidence that it is in any other animal either, and so does not need to be treated with anything other than respect. Finally, I do not discuss castration or mutilation at any point, so again I am not sure why you added it to your comment.