As spring arrives, you may notice a new visitor sucking nectar from hummingbird feeders and picking juicy fruits from shrubs and trees.
The Swinhoe’s white-eye is a tiny bird with chartreuse plumage, native to places like Southeast Asia, whose population appears to be growing rapidly throughout Southern and Central California.
Nearly two decades ago, there was just a small number of them living in Orange County, likely arriving as a result of the pet trade. Now, they can be found as far south as Baja and as far north as San Luis Obispo.
A paper recently published in the journal Biological Invasions suggests that given their solid growth in recent years, their population could be on the precipice of exploding.
“Their distribution in Southern California is expanding really rapidly. The range map that we put in the paper that's like six months to a year old now is already out of date,” said Devon DeRaad, Ph.D. student at the University of Kansas Natural History Museum and lead author of the paper.
What makes their expansion especially interesting is that the California habitats they’re expanding into aren’t like the warm, humid, subtropical habitats they go to in places like China, Vietnam and Malaysia.
“It's not totally clear to us still why they're able to survive and reproduce and seemingly thrive in Southern California,” said DeRaad.
What’s going on?
They seem to avoid native oak woodlands, deserts and chaparral in favor of developed urban environments, which in California, tend to have tons of ornamental flowers and fruit trees kept alive with supplemental irrigation. They could’ve adapted to using these sources of food quite successfully, much in the way that the screeching parrots from Mexico have.
At least part of the increase could be chalked up to a documentation issue, as researchers rely on pictures from the public to document bird populations. Maybe people are just more focused on them now?
Their population could’ve just grown enough for them to reproduce prolifically. It’s not unheard of for a population to show up, hang out in small numbers for many years and then explode as they adapt to the surrounding areas.
Or maybe … they’re just really good colonizers. They did establish themselves offshore on the Channel Islands after all.
The good news is that as of right now, they don’t appear to be invasive.
There are more than 100 species of white-eye around the world, and it’s been confirmed that these aren’t the same white-eye as those that’ve taken over Hawaii and displaced native birds.
While the expansion of their populations likely means fewer resources for other animals, it’s unclear if they’re impacting any native species negatively. They largely avoid drier and less verdant native habitats, sticking to modified urban areas. That said, further research is needed.
“So far, we haven’t seen any negative consequences on native species, but that could change at any time,” said Allison Schultz, associate curator of ornithology at the Natural History Museum of Los Angeles County, and co-author on the paper.
European starlings, for instance, nest in tree cavities and displace native birds like woodpeckers.
It’s tough to accurately track bird movement and population size, so researchers often turn to user supplied data from the iNaturalist app and the eBird website from Cornell University to help build their databases.
The iNaturalist app is free and can help you identify birds, plants and insects. If you download it and start taking pictures of various nature-ey things that you find, you too will likely be helping a researcher somewhere.
The Swinhoe’s white-eyes seem to be attracted to hummingbird feeders, and fruiting trees and shrubs in developed urban areas. So keep an eye out at parks and in your yard. They’re pretty zippy, so you’ll have to move fast.
