DIANE BELL
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“Western Birds” and curator of birds at the S.D. Natural History Museum, says it’s the largest robin incursion on record in 50 years. The last time such giant robin flocks were sighted locally was in 1972-73 and, in even greater numbers, in 1961-’62 and 1957-’58, according to the annual Christmas oneday bird count here.
He says that since 2005 we’ve had very few robin sightings — probably limited to those in the small resident breeding population that began colonizing here, primarily in the mountains, in about 1940. But that population has dwindled over the past 20 years, Unitt says.
So, imagine bird watchers’ delight when a bird count Dec. 23 in Escondido recorded 695 robins, and a Dec. 27 count in Rancho Santa Fe logged 3,789. “The robins’ long downhill slide locally makes this year’s invasion all the more surprising,” Unitt says.
The experts don’t know the exact origin of these robins — who winter in large numbers in the Pacific Northwest and northern states — or why they came.
Is it stormy weather? Cold temperatures and snow? Scarce food and water supplies? It’s anyone’s guess. It could be all these things, and more — a
perfect storm.
There long have been occasional sightings in the county of single robins or a few pairs of robins, explains Lehman, who goes bird watching every day. He estimates that as many as 50 to 100 breeding pairs are scattered throughout the county.
It’s not unusual to see a robin or two at higher elevations, such as in Julian, or the Palomar, Laguna and Cuyamaca mountains, he says.
But now they are flocking to areas such as La Jolla’s coast, Balboa Park, Point Loma, Del Cerro, Encinitas, Vista, Lake Hodges, Escondido, Chula Vista, and even the Salton Sea and Anza-Borrego Desert. They’re even being spotted in Baja California.
The explosion of these birds actually has a name. “The term for this phenomenon is ‘irruption,’ ” adds Jen Hajj, San Diego Audubon Society event coordinator. An irruption is a sudden change in population density. It tends to be a migratory event when northern birds go somewhere they’re not usually expected — often in search of food.
“It seems that everyone is scratching their heads on this one,” Hajj says. “We can name the phenomenon, but can’t really say why it is happening. All we can do is stand in awe of the mystery.”
“How many? Who knows?” Lehman says. “Tens of thousands,” he guesses. Unitt agrees.
Lehman checked in with colleagues in Northern
California, Washington, Oregon, Vancouver, British Columbia and northern states where robins often winter to ask if they had fewer robins this year.
No, he was informed, winter robin populations were thriving there as well.
“Wherever they should have wintered, they didn’t like this year,” theorizes Lehman. Since American robins are extremely hardy and used to cold weather, he doesn’t believe dropping temperatures or increased snow would have fazed them.
“The usual explanation is lack of food,” he says.
“There could have also been a stellar breeding season last spring/summer, and now there’s just a lot more robins in these flocks (but I think this is the least likely),” adds Nick Thorpe, who works at the Zoo and S.D. Audubon Society. “There’s a lot of variables in migration patterns, so it’s hard to know for sure why a bird would end up in a particular place in one particular year.”
Unitt theorizes they may be coming from northeast of us, from the Great Basin and Rocky Mountain states where there is a heavy snow pack this winter. Perhaps some of the robins’ fruitbearing shrubs failed to produce this year.
As for the stereotypical image of robins in the East and Midwest eating earthworms and grubs, that’s common in the spring and summer, but robins feed principally on berries in the winter, says Unitt.
In San Diego, they are devouring berries from Brazilian pepper trees, carrotwood trees, camphor trees, Hollywood junipers, pygmy palms, pyracantha bushes and toyon shrubs. Even after our recent rains, Lehman says he rarely saw them chowing down on worms.
However, Claudia Allen, who reported more than 100 robins descending on her yard south of UC San Diego on two recent days, said that, in addition to berries, they were pecking at something in the new mulch.
A lot of folks have noticed flocks of smaller crested waxwings mixed in with the robins. That is not unusual, Lehman says, because waxwings eat the same diet as robins, and they are regular visitors here in the winter.
When will the robin visitors depart?
“Who knows,” Lehman says. “It could be tomorrow, or they could stay until March.”
Will they come back next year? “History tells us not to expect invasions in successive winters,” Unitt says.
A best bet for those who have robins on their San Diego bucket list, is to venture out to the San Diego Zoo parking lot about 6:15 a.m., Lehman suggests. If they are there, sunrise is when they take off in huge flocks to hunt for food. They’ll come back just before dusk — if they do return.