The bird had also begun to gather things to build a nest, Ms Mitchell said.
It sounded as though the seagull was in love with itself, Auckland Zoo's birds team leader Todd Jenkinson said.
"If he's building a nest then potentially he thinks he has found a mate," Mr Jenkinson said.
"If a seagull has an intruder in their habitat then they wouldn't be comfortable enough to fly away and gather things for a nest."
Unfortunately the bird probably does not have the brain capacity to clue up and realise its 'mate' is its reflection, Mr Jenkinson said.
Its next move will depend on whether the seagull is a male or female.
"If it is male and building a nest and then the 'mate' doesn't lay any eggs, then it might realise it's hopeless and move on.
"But if it is a female it might even sit on eggs. You find single females in captivity lay eggs ... regardless of whether they are being mated or not."