"Grossed out" by the morbid discovery, the woman rang an 0800 telephone number printed on the plastic salad packaging.
She received an immediate apology and yesterday was told a supermarket staff member would collect the salad pack from her home in order to investigate how a dead bird came to be sealed inside.
The woman said she was happy with Countdown's handling of the situation, but would think twice about buying packaged lettuce for a while.
Countdown spokesman Luke Schepen said the incident was believed to be a one-off.
The product batch had an expiry date of September 1, 2012 and so it was unlikely any further stock was on sale, he said.
"Food safety and quality is of the utmost importance and this investigation is now underway as a matter of urgency," Mr Schepen said.
The packaged salad was manufactured by a Countdown supplier at a South Island facility, which did not produce stock for retail in the North Island, he said.