Washington DC - Some might call it fowl play to joke about their age, but President Joe Biden made light of turning 81 as he spent his birthday pardoning two Thanksgiving turkeys on Monday.

The oldest sitting president in US history, whose age is a concern for voters in opinion polls, said he had received a rendition of "Happy Birthday" before the annual ceremony at the White House.

"I just want you to know it's difficult turning 60," Biden then said with a chuckle before officially sparing the two turkeys, named Liberty and Bell, from ending up on the Thanksgiving dinner table.

It was just one of a series of quips by Biden - who would be 82 if reelected to a second term next year and 86 when he left the Oval Office.

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"This is the 76th anniversary of this event - and I want you to know I wasn't there for the first one," he said in another light-hearted moment.

Liberty the turkey, who was placed on a box alongside Biden on a podium for the ceremony on the South Lawn of the White House, gave an approving gobble as Biden issued the presidential pardon.

One of Biden's jokes, however, missed the mark when he appeared to confuse superstar singers Taylor Swift and Britney Spears.

Biden said Liberty and Bell "had to beat tough odds" to be chosen for a pardon, adding that it was harder than getting a ticket to Beyoncé's Renaissance World Tour "or Britney's tour... it's kinda warm in Brazil right now."

It was Swift who had postponed a show in the Brazilian city of Rio de Janeiro on Saturday due to extreme heat after a fan died at the singer's concert the previous night.

Biden, First Lady Jill Biden, and members of the presidential family will be heading to the exclusive island of Nantucket on Tuesday to spend the Thanksgiving holiday there.