As thousands crammed into downtown Baton Rouge on Sunday morning, the air was filled with barking, yapping and the sound of bagpipes.

The occasion was the 16th annual CAAWS Mystic Krewe of Mutts parade, which featured hundreds of dogs marching or gathering on both sides of downtown city streets to watch, from towering Great Danes to a tiny Maltese. Many of the dogs and their owners sported superhero costumes, often matching, as they filled the parade route, starting at North Boulevard Town Square.

Men with bagpipes started the parade, followed closely by the Royal Court, which was made up of dogs with titles such as King Milo and Queen Dini, Lord Huey and Prince Tom-Tom. About a dozen dogs on leashes followed closely behind the royalty, all wearing miniature jerseys reading “adopt me.”

“Parades are such an integral part of Louisiana, and this is a wonderful way to let people know what we do and join in,” said Glenda Parks, president of the Capital Area Animal Welfare Society, or CAAWS, which organizes the event. The group’s volunteers help rescue animals from “kill shelters” and link them up with adoptive families. The parade’s proceeds go toward CAAWS’ spay & neuter fund.

The parade’s 2015 theme was “Marvelous Mutts,” a reference to comic-book superheroes — which became vividly clear at a costume contest held several hours before the parade.

Dogs were dressed as the Incredible Hulk, Batman and members of the Incredibles. Terry Price and his family dressed in Captain America outfits, and Price even built a Captain America-themed float out of a wagon, then mounted a homemade doghouse made from cedar, complete with stairs to an upper level and adorned in Captain America colors. At the top of the float sat their Maltese, Sparky and Putt Putt.

Two English bulldogs, Banner and Bentley, were outfitted as the Hulk and the Thing and their owners pulled them along in a wagon painted to look like a holding pen.

Another group included family members and friends and their two basset hounds, Cleopatra and Socrates, dressed as “Middle-Aged Mutant Ninja Turtles Hounds.”

“We thought about doing Teenage Mutant Ninja Turtles … but we’re all middle-aged,” team member Julie Sears said.

The event showcased various animal shelters in the Baton Rouge area, like Cat Haven, which organized 847 adoptions in 2014 and has about 80 cats and kittens in its shelter at a given time, said the group’s president, Wendy Decker. Six cats up for adoption were on display, which attracted the adoration of passersby — but Decker said they don’t necessarily expect to find owners at the event.

“People don’t usually come to a parade expecting to buy a cat,” she said.

There was also Red Stick German Shepherd Rescue, which saves pure-bred German shepherds from kill shelters and then rehabilitates them in private foster homes before finding them permanent homes, said the group’s president, Maggie Thomas. As for why the group focused on that one breed, Thomas laughed, “We’re German shepherd people.”

As the parade kicked off, residents lined North Boulevard and several dogs barked at other pets as they marched by. One resident along North Boulevard was Brien Buxton, who lives a block from the route and has attended the parade with friends and family for the past six years. His goldendoodle, Talluah Jane, was dressed as My Little Pony.

Another resident along the route was Whitney Grier, who dressed her dog — Mr. Bates, named after the “Downton Abbey” character — in a Hawaiian T-shirt because of his laid-back personality. She said she found about $60 worth of dog treats for Bates from various vendors at the event — including one dog dessert that had been crafted as a personal-sized cake.

“He has already eaten his weight in treats,” Grier laughed.

Follow Daniel Bethencourt on Twitter, @_dbethencourt.