No - when saying "This is [something]" you always have to use a phrase 'To jest...', regardless of the gender of the noun.
Not exactly. You can say "Ta jest ...", "Ten jest ...", but: there are 2 variants.
In the long version, you can use words "ten/ta/to", but this type of structure is used to show some sort of respect, admiration, and is used with particle "dopiero" instead of verb "być", which then can be followed by noun in the nominative case:
- "Ta, to dopiero kaczka!" or shorter "To dopiero kaczka!" = "What a (great/tasty/adorable) duck is it!"
- "Ten, to dopiero bohater!" or shorter "To dopiero bohater!" = "A hero he is!"
Attention! when used with "też" or "też mi dopiero" (to me, only) - it completely changes its meaning. It is then an expression of doubt or mockery:
- "Też mi dopiero bohater" or shorter "Też mi bohater" = "Phew, what a hero is he".
- "Też mi dopiero kaczka" or "Też mi kaczka" = "It is a duck, my foot"
In the short version, you are obliged to use instrumental case with "on/ona/oni/one", and it rather means occupation, present state etc. So, while talking like this about animals, you are indicating that someone either has some professional occupation, or is dressed (to be a dog, a duck) for example for a party. But attention! This can also mean derogatory speech!
"On jest psem" (male, singular, instrumental case) = "He is dressed do be a dog"; but also can be "He is not a man! He is a dog!"
"Oni są psami" (male, plural, instrumental case) = "They are dressed do be dogs", but also can be "They are not men! They are some dogs!"
"Oni są strażakami (male, plural, instrumental case) = "They are firemen";
"Ona jest kaczką" (female, singular, instrumental case) = "She is dressed to be a duck";
"One są pokojówkami" (female, plural, instrumental case) = "They are room maids".
Is this really correct? Until now I learned either "To kaczka" or "To jest kaczką".
"To jest kaczka" is the best, and "To kaczka" is correct.
"To jest kaczką" is wrong, because you use this construction when the subject of the phrase is a noun. What you propose, is a noun is noun structure - therefore you cannot use the construction with "to jest" + noun in nominative if the subject of the phrase is a pronoun - and in this phrase "to" works as a pronoun in the function of subject ("to" may serve also other functions, see here)
See more here: A guide on "X is Y" and "This is Y" constructions