Residents of Iowa City have been treated to some visitors earlier than usual this year — robins have come flocking back to town before their normal migration time.

Diane Porter, an owner of Birdwatching Dot Com and a writer for Bird Watchers Digest, said that most robins go south for the winter, but many do stay here in forests.

Most people associate the arrival of robins with the start of spring, but this year’s early arrival could indicate something else.

“People in the cities don’t usually see robins in the winter,” Porter said. “If they’re coming to town, they may be stretched for food.”

Chris Edwards of the Iowa City Bird Club said most robins don’t migrate back to Iowa until late February or early March.

According to the Iowa City Bird Club annual Christmas Bird Count, the number of robins in the area were above average but then dropped again in January.

“It’s been unusual to see such large numbers show up at the beginning of February,” Edwards said.

The robins’ appearance was probably related to food, he said, and that Iowa “must have had a good fruit crop.”

While Porter said that food might have been a reason for the birds’ appearance, there were other factors to consider, and weather being one of them.

“The time of year that’s hardest for wintering birds is now, at the end of winter,” she said.

Robins survive the winter weather of Iowa by fluffing up their down feathers to help them retain their 106º temperature, Porter said. They also burrow into evergreen or juniper trees, she said.

“That’s why birds you see in the winter look so round, because they’re all fluffed out,” Porter said.

The weather in Iowa over the winter has been colder than in years past, which Porter said could account for the higher number of robins around town.

“It’s normal for food to get scarce, but we’ve had very mild winters over the past few years,” Porter said. “A few more robins might have stayed, which may have used up their resources quicker.”

As the weather warms up, more robins are likely to make themselves known to search for earthworms or puddles of water, because during the winter they must usually eat snow for water.

Liz Christiansen, the director of the University of Iowa Office of Sustainability and a longtime birdwatcher, said she had seen many robins crowding in trees for fruit.

“They have been more visible because they flock in trees until all the berries are gone,” Christiansen said. “It’s been a hard winter for everyone, including the birds, and they’re eating to survive.”