U.S. citizens are celebrating their annual Thanksgiving holiday — a centuries-old harvest time tradition.

The week of the Thanksgiving holiday is one of the busiest travel weeks of the year, as Americans take to the air, railways and roads to visit family and friends and share a celebratory dinner.

The Thanksgiving Day meal usually includes turkey or ham, vegetables, and pies made of fall-harvest fillings such as apple or pumpkin. The National Turkey Federation estimates that, overall, Americans consumed more than 46 million turkeys at Thanksgiving last year.

After the feast, some people engage in recreational activities such as watching or playing sports — although, after such a heavy meal, a Thanksgiving Day nap is also a well-established custom.

Some Americans spend at least part of the day doing charity work, such as helping serve a Thanksgiving meal at a homeless shelter.

President Barack Obama released a holiday message Thursday, urging Americans facing difficult economic times to believe in the nation's ability to meet its challenges.

In a recorded message, he said the nation's problems did not develop overnight and will not be solved overnight. He encouraged U.S. citizens to remember service members overseas, and he thanked those people taking time out to do volunteer work on the holiday.

On Wednesday, Mr. Obama gave his annual “pardon” to the national Thanksgiving turkey and its alternate, an act that symbolically — and humorously — “saves” the birds from becoming part of a traditional Thanksgiving Day feast.

At the pardoning ceremony, Mr. Obama said people should be thankful for what they have and remember those who have less. He also thanked members of the U.S. military for their service. His two daughters, Sasha and Malia, were with him at the event.

The turkeys, named “Liberty” and “Peace,” will live near Washington, D.C. at the estate of the first U.S. president, George Washington, where they will be part of a Christmas program until January.

Later Wednesday, Mr. Obama and his family took two other turkeys to a Washington area food bank that helps feed those in need. While there, the Obamas helped distribute food bags.

In 1863, President Abraham Lincoln issued a proclamation calling for the last Thursday of November to be observed as a day of thanksgiving. The modern Thanksgiving holiday traces its roots to 1621, when English settlers in the Massachusetts Colony held a feast with a Native American tribe that taught the colonists how to grow food and hunt for game in their new surroundings.

Thanksgiving turkeys have been presented to presidents intermittently since the Lincoln administration. President George H. W. Bush issued the first turkey pardon 20 years ago.