"These are three pigeons."

Translation: ये तीन कबूतर हैं।

[justusbalentine]

कबूतरें isn't plural pigeon?

[Zesul]

Nope. Masculine nouns that end in a consonant do not change on pluralization (so long as they are in direct case). कबूतरें would have been correct had कबूतर been feminine.