Republicans, a rare breed in New York City politics, may now qualify for the endangered species list.
Peter Koo, a councilman from Queens who was elected as a Republican in 2009, officially defected to the Democratic Party on Monday, reducing the Republican contingent on the Council to four, or 7.8 percent of its 51 members.
Mr. Koo, an immigrant from Hong Kong who started a chain of pharmacies in Flushing, said he had been lured by the reach and influence of the Democratic leadership in his borough. But he also said that the anti-immigrant tenor of the national Republican Party had played a role in his decision.
“They can do more, surely they can do more to attract different minority groups to join the party,” Mr. Koo said, when asked about the policies of the Republican candidates for president. “So far, they haven’t done enough.”
He spoke of his support for the Dream Act, federal legislation that would make it easier for some illegal immigrants who arrived in the country as minors to become permanent residents. The bill is vociferously opposed by many of the leading Republican presidential candidates.
“People have come here for so long,” Mr. Koo said. “We are supposed to have a way for them to stay here, instead of turning our back to them and forcing them to go back to their countries.”
“It’s not fair to them,” he added. “I understand how hard it is to be a newcomer.”
Mr. Koo is known as a centrist on the Council, and as a businessman, he often takes positions traditionally held by more conservative politicians. But he has actively sought to protect the rights of the city’s immigrants.
At his announcement on Monday, Mr. Koo was surrounded by top Queens Democrats, who described his defection as a “a New Year’s gift,” referring to the Chinese New Year, which began on Monday.
Rory I. Lancman, a Democratic state assemblyman from Queens, joked that he had been surprised when Mr. Koo had initially sought office as a Republican. After all, Mr. Lancman said, “he’s a nice guy, he likes people, he likes the immigrant community.”
The line drew hearty laughter from the crowd, and, later, Mr. Koo made his own confession: “From the beginning,” he said, “I am always a Democrat at heart.”