PITTSBURGH (KDKA) — Fans at Heinz Field were delighted over the weekend by live penguins from the Pittsburgh Zoo & PPG Aquarium waddling on the ice during the 2017 Coors Light NHL Stadium Series between the Pittsburgh Penguins and the Philadelphia Flyers.

Others, however, were less delighted.

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In a letter sent to the Pittsburgh Penguins, People for the Ethical Treatment of Animals admonished the use of the animals during the game, saying the birds were sent “scrambling in terror” after being scared by fireworks.

“It’s inherently stressful for wild animals like penguins to be hauled around, used as props, and exposed to noisy crowds, with or without explosives going off,” says PETA Executive Vice President Tracy Reiman. “PETA is calling for the only Penguins on the ice at Heinz Field to be humans on skates.”

The letter is finished with a request: “Will you please let us know that you won’t use live animals for promotions in the future?”

Around 2:30 p.m., the Pittsburgh Zoo & PPG Aquarium responded the the criticism by defending the use of the penguins, saying that the safety of the animals is their top priority.

“The NHL worked with us to ensure that the penguins would be safe and enjoy their visit to Heinz Field,” the statement said, in part. “The penguins who attended the Winter Classic are some of the same penguins that participate in our weekend Penguins on Parade event. They are very comfortable around people and noises.”

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As for the penguins’ reaction to the fireworks? The Zoo says the reaction lasted “less than 10 seconds,” before the birds were back to playing on the ice.

“The loud pop from the pyro technical display temporarily startled the penguins and their first reaction, similar to a human’s when startled, they flapped their wings.”

But, PETA wasn’t about to accept the zoo’s explanation.

Around 7 p.m., another statement was sent responding to the Pittsburgh Zoo & PPG Aquarium.

“These penguins were terrified into a flight response—there’s simply no refuting that. While human beings were able to realize that the fireworks were merely startling and not dangerous, these penguins were obviously frightened and attempted to flee,” the statement read, in part.

PETA ended the message by saying the zoo should “do better by the animals in its care.”

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