If you think that masculine nouns are always used with referring to males and feminine nouns when referring to females, your assumption would be wrong — especially when talking about animals.
Like most nouns, the names for nearly all animals are either masculine or feminine. For example, the word for giraffe, jirafa is feminine, and it can be used when referring to any giraffe, whether male or female. Similarly, rinoceronte is masculine, and it can be used to refer to rhinoceroses of either sex.
Some animals have different names for each sex. For example, a perro is a male dog, and a perra is a female dog. The names don't have to be so similar: a cow is una vaca, while a bull is un toro, even though they refer to the same species of animal.
Some other animals with different names for the sexes are:
- el lagarto (male lizard), la lagarta (female lizard)
- el elefante (male elephant), la elefanta (female elephant)
- el caballo (stallion), la yegua (mare)
- el carnero (ram), la oveja (sheep)
- el gallo (rooster), la gallina (hen)
- el macho (billy goat), la cabra (nanny goat)
Generally, the masculine form can be thought of as the default name for the type of species. Thus if you don't know whether a cat is male or female, it's fine to refer to it as un gato. But a cat known to be female can be referred to as una gata.
In the case of animals whose names vary with the sex, if you have a group of animals, some female and some male, they should be referred to by the masculine plural: thus los gatos or los perros. But if the name of the animal is invariably feminine, the feminine must still be used: las jirafas (even for a group of males) or las arañas (spiders). In a very few cases where each sex has a different name — they include vaca, cabra and oveja — the feminine form can be pluralized to represent a group. (The same can be true in English, as cattle might informally be referred to as cows even if some bulls are part of the mix.)
If you need to indicate the sex of an animal with a undifferentiated name, you can add the word macho for male or hembra for female:
- la jirafa hembra, the female giraffe
- la jirafa macho, the male giraffe
- el dinosaurio macho, the male dinosaur
- el dinosaurio hembra, the female dinosaur
Note that macho and hembra, however, are traditionally considered to be either nouns or invariable adjectives. Thus they do not vary in form with gender or number:
- las jirafas hembra, the female giraffes
- las jirafas macho, the male giraffes
Although treating macho and hembra as invariable adjectives is the grammatically safe thing to do, in real life speakers sometimes make them plural. (Some other grammar rules may also be followed loosely by native speakers.) You should stick to the traditional form in formal writing, however.
When referring to animals with personal names (such as pets), you should use adjectives whose gender matches the given name of the animal when using that name as the subject of a sentence:
- Pablo, la jirafa más alta del zoo, está enfermo. Pablo, the zoo's tallest giraffe, is sick.
- Su hámster se llama Elena. Elena es muy guapa. His hamster is named Elena. Elena is very pretty.
Have a question or comment? See the blog post on animal gender.