I'm the seagull. No, that's not it. I'm an actress. That's it.
The seagull comes to mean several things during the course of the play. In Act Four, Nina uses the seagull Treplev shot in Act Two as a symbol of her fall from grace. She recently signed letter to Treplev not as "Nina" but as "The Seagull." Nina combines two ideas together to create her symbolic self- description of the seagull. The dominant reference is to Trigorin's metaphor of Nina as the seagull. She describes herself to Treplev as the seagull in confirmation of the tragic fact that Trigorin did attempt to ruin Nina exactly as he said he would in Act Two.
But Nina is not completely destroyed. Her fractured language sounds like the speech of a troubled soul, but amidst her rambling is sense and conviction. She has lost her innocence, her lover, a baby, and financial stability, but she has her pride and her will to endure. She refutes her original statement, "I'm the seagull," with "I'm an actress." Nina stays afloat by holding on to her dream, however disappointing it has turned out to be and takes pride in her ability to withstand her disappointment. This quote also refers to Pushkin's story about a miller who signs his name "The Raven." Chekhov puns "The Seagull" with "The Raven," commenting to his audience "No, that's not it," indicating that he knows he has ripped off of a commonly known subject.