In Rochesterbet88, N.Y., there are telltale signs that the holiday season is underway.

Santa’s workshop opens at the outdoor ice rink downtown. There is the lighting of the pyramid of kegs at the local brewery. Productions of “A Christmas Carol” and “The Nutcracker” begin.

Then there are the tens of thousands of crows that descend on the city every day at dusk in early December, and the fireworks and lasers that are deployed to drive them away.

City officials and wildlife experts estimate upward of 20,000 crows roost downtown nightly.

“It’s like you’re in ‘The Birds,’” said Rachel Kudiba, referring to Alfred Hitchcock’s classic film about birds on a murderous rampage. Ms. Kudiba was one of four U.S. Department of Agriculture Wildlife Services specialists hired by the city to chase and haze the massive groups of crows.

An outbreak of West Nile virus decimated the American crow population in the early 2000s.

But no one would know it by the sight of the cawing, swirling cloud of jet-black crows over the waterfalls of the Genesee River. They come from miles around, wildlife experts say, seeking warmth in the city’s concrete grid and ambient light after foraging in fields.

The phenomenon plays out in urban centers, with reports of large roosts wintering in upstate New York cities like Albany, Auburn, and Poughkeepsie; in Danville, Ill., in the Midwest; and in Portland, Ore., and Sunnyvale, Calif., in the West.

Many cities have employed scare tactics to ward them off. But few seem as consistent in their regimen as Rochester, where the annual Yuletide ritual of shooing crows began in 2012.

Such a scenario would represent a notable degree of ticket-splitting, perpetuating a trend captured by surveys throughout this election cycle. Democratic Senate candidates in a number of swing states, including Arizona and Nevada, have consistently polled ahead of the top of the ticket, especially when President Biden was the party’s standard-bearer. As Ms. Harris’s nomination has made the election more competitive, the gap between her and those down-ballot Democrats has narrowed — but the trend persists in most races in swing states.

Ms. Harris may give remarks about border issues during the visit, according to the people, who insisted on anonymity to discuss a trip that has not yet been made public. The people said final details about exactly where Ms. Harris would visit or what else she might do on the trip have not been decided. The Harris campaign did not immediately provide a comment.

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