Celebrated on the fourth Thursday of November, Thanksgiving leads off the winter holiday season in America. While it has historical roots in religious and cultural traditions — beginning as a day of giving thanks for the blessing of a harvest — it has evolved into a largely secular holiday.

For most of us, it is a day for a gathering of family and friends over a dining table laden with turkey and all the trimmings.

Thanksgiving has been with us since Europeans first landed on our shores, so there’s plenty of history, some mystery, and plenty of fun facts and figures associated with the holiday. So here’s a bit of turkey day trivia to mull over as Thanksgiving 2018 approaches:

Most historians agree that the first Thanksgiving in America was celebrated by English Pilgrims at Plymouth Colony in Massachusetts sometime between September and November in 1621. It was said to have been a three-day harvest festival carried out by colonists in the company of native Wamparoag peoples. Some in Virginia, however, argue that its colonists were the initial Thanksgiving celebrants.

Texan historians dispute both of those claims, contending that the first Thanksgiving observation in America occurred in what is present-day El Paso, celebrated by Spanish explorer Juan de Oñate and his expedition in 1598. Oñate’s expedition marked the beginning of Spanish colonization of the American Southwest.

President George Washington proclaimed the first nationwide thanksgiving celebration in America, marking November 26, 1789 "as a day of public thanksgiving and prayer…"

Thanksgiving is not just an American holiday. Canada celebrates it on the second Monday of October, and it also is observed in a few Caribbean islands and in Liberia. Similar festival holidays also occur in Germany and Japan.

Many American cities host Thanksgiving Day parades. The tradition began in Philadelphia in 1920 with Gimbel’s Thanksgiving Day Parade (now 6ABC Dunkin’ Donut’s Thanksgiving Day Parade). Largest and most famous of the parades is Macy’s Thanksgiving Day Parade in New York City. It draws 3.5 million live spectators and 50 million more watch it on television.

Turkeys have historically served as the centerpiece dish on Thanksgiving Day dining tables. Originally they were wild birds, but nowadays they’re the product of a huge agri-industry that in the U.S. last year processed 242.5 million turkeys.

Wild turkeys can run at speeds of up to 12 mph, can fly, and are adept at swimming.

Minnesota is the top turkey-producing state, currently turning out 42 million birds a year — followed by North Carolina at 32.5 million.

In 2017, Americans consumed 16.7 pounds of turkey per person.

American consumers devour between 45 and 50 million turkeys each Thanksgiving.

Feel sleepy after stuffing yourself with turkey? No surprise, because turkey meat contains tryptophan, an amino acid that tends to induce sleepiness in some people.

Turkey is a low-calorie and nutritious food. A three-ounce serving of skinless breast contains approximately 100 calories, 26 grams of protein and just 2.5 grams of fat. It also is naturally low in sodium and sugars.

Ben Franklin once reasoned that the turkey would be a better choice for the national bird than the bald eagle. The eagle, he said, "Is a Bird of bad moral Character…He does not get his Living honestly." On the other hand, he declared, "The Turkey is in Comparison a much more respectable Bird."

Football is an important part of Thanksgiving Day celebrations in many American homes. It’s the biggest day of the NFL regular season with three games scheduled for broadcast on national TV: The Chicago Bears vs. the Detroit Lions (12:30 p.m. ET), the Washington Redskins vs. the Dallas Cowboys (4:30 p.m. ET) and the Atlanta Falcons vs. the New Orleans Saints (8:20 pm ET).