SAN DIEGO – Tens of thousands of American robins have been flocking to San Diego this winter for the first time in nearly 30 years.

“You’d have to be a pretty old timer to remember anything like this previously,” Philip Unitt, curator of the Department of Birds and Mammals at the San Diego History Museum, said to “We’re having the biggest invasion that we’ve had in at least 50 years and probably longer.”

The birds first started flocking to the region back in December, Unitt said, and the number has only grown from there.

As Unitt explained, the robin’s migration pattern is fairly erratic, mostly moving to and from places based on the availability of berries and other small feed off trees.

“The robin is a kind of complex species…The flocks move around nomadically to exploit fruiting trees,” he said. “Once they strip a tree of its fruit, then they’ll move on.”

Many San Diegans might have seen that happen in their own backyard. Unitt said that the birds love feeding on native plants, eating things like Christmas berries, as well as fruit from fig and camphor trees.

Robins came to the region south of the San Bernardino Mountains during winter in an irregular pattern of large migrations in some years, with smaller migrations in others. 

In 1940, however, they started spreading south as a breeding bird, as more urbanization in the region created more of a habitat for robins year round with things like new lawns and backyards.

Up until the recent invasion though, that local population had dwindled to next to nothing and migratory trips through the region had become few and far between.

While it’s hard to pinpoint exactly how many birds are still currently in San Diego, Unitt expects them to stick around for another couple weeks in smaller numbers, as many will start traveling back to where they came from – likely somewhere in the Northern Rocky Mountain states.

“Enjoy them while they last,” Unitt said. “It’s possible that some will stay to replenish the local breeding population, but more than likely they will head back north within the next month or so.”

He also stresses that if anyone comes across any birds behaving oddly or appear to be injured to take them to a local veterinary provider, like Project Wildlife with the San Diego Humane Society.