VEGA BAJA, P.R. — Hiram Figueroa rears roosters to fight, a Puerto Rican tradition from the time of the Spanish colonists that he learned as a teenager half a century ago and later taught his son. Together, they exercise their birds, clip their feathers and give them delicate sponge baths.

Now rows of dusty cages lie empty in Mr. Figueroa’s backyard, a reminder of his fading livelihood.

He used to keep some 250 game fowl tucked behind their modest home in Vega Baja, a town west of San Juan , the capital. Now he is down to about half, a drop big enough that a neighbor told him that sometimes he no longer hears the incessant crowing. The men who own most of the birds and pay the Figueroas for their care bought fewer chicks this year, knowing they would not need them for long.

Cockfighting will be outlawed in Puerto Rico and other United States territories in December, a long overdue ban in the eyes of animal welfare advocates who consider the practice cruel and outdated. Louisiana, the last state to allow cockfighting , prohibited it more than a decade ago, in 2008. But unlike state legislation, which was enacted by elected representatives, this ban was passed by Congress, where Puerto Rico’s 3.2 million people do not have a voting member. Lawmakers slipped the ban into last year’s farm bill, catching even the Puerto Rican government by surprise.