How a UCLA sparrow population could be a blueprint for wildlife vitality in changing cities

The dark-eyed juncos living on campus are not being faithful, and that's not the half of it. On the tails of a breeding season that's seemed more like a telenovela to those closely watching, the little sparrows have left researchers with more questions than answers as the last of the season's offspring leave their nests.

For starters, the juncos - who number around 300 and have been observed thriving at UCLA for a couple of decades - are breeding months earlier than normal. They're building nests higher off the ground and on artificial structures, and breaking records for rounds of eggs laid. They're also blurring the lines with breeding fidelity - something often seen in various bird species yet which still raises many questions, according to UCLA researchers.

Keeping track of the juncos' comings and goings on campus and elsewhere is doctoral student Joey Di Liberto, an ecologist and naturalist who is rarely spotted without his rugged wide-brim fedora and binoculars in hand. Constant bird surveillance is something the San Fernando Valley native is used to doing, especially since joining the Yeh Lab at UCLA, where he and dozens of other students build on Professor Pamela Yeh's extensive scholarship about how local birds are affected by the urban landscape and its unique environmental stressors.

For nearly a decade, Di Liberto has studied the evolutionary biology of animals in relation to anthropogenic change. He's worked closely with bees, birds, reptiles and once, for their whole breeding season, house sparrows living in polluted Australian mining towns. The driver of Di Liberto's work, he says, is how humans are modifying the planet, and how animals on the front lines are responding.

The juncos are of particular interest to Di Liberto, Yeh and other researchers in Southern California because of their observed "behavioral plasticity," or their ability to change behavior in tandem with changes in the environment. Besides the convenience of monitoring juncos on the UCLA campus, this once-migratory population started staying year-round about three decades ago, making it easier for researchers to study them. The juncos' habitats among UCLA's buildings and green spaces also make for a good sample environment due to the representation of urban indexes around them, he says.

During a July morning walk around campus, a fluttering of wings catches Di Liberto's eye near Ackerman Union. This set of wings belongs to a female junco named Hoops - a favorite of the researcher, who can immediately identify her, thanks to the unique combination of stacked colored bands secured around her leg. Hoops' dark green and aluminum banding on the right leg and dark green and lavender combo on the left are among some 200 variations that Di Liberto has memorized.

Hoops, approximately 2 years old, rose to notoriety this season after nesting with Florence - a much older male junco who has nested on campus since 2018. After building a nest together on top of a wall-hidden light fixture, the pair had three rounds of eggs together, also known as a clutch. The third clutch died after Florence suspiciously disappeared, leaving Hoops with the hatchlings. Di Liberto says that's when another male named Chase started showing up, eventually taking Hoops with him to start a new nest on a low pine tree branch off Bruinwalk.

Around the same time the pair built that nest, Chase was also nesting a ways off, in a spot under a low bush, with an unbanded female Di Liberto calls Pursuit. However, the verdict is still out as to whether Chase is the father of this female's clutch. Chase was less than helpful in building the nest, and when the eggs hatched, a male named String Cheese started showing up to defend the nest. With blood samples and thus the DNA of all captured birds and nestlings, Yeh lab researchers have future plans to conduct genetic work to study paternity in situations like this.

"There's a whole 'Maury'situation here," said Di Liberto, who, junco drama aside, is more interested in Florence and Hoops' nesting preference - real estate atop an artificial structure high off the ground. "They're well-constructed nests, but for juncos who normally nest on the ground, these nests are very abnormal. Juncos have figured this out in just 20 years or so, which is very quick. And our lab's past work has shown it's helping the nestlings survive."

But similar observations of the UCLA juncos and populations elsewhere over the last few decades still leave researchers wondering why the species has altered its breeding habits so swiftly and what it indicates about the juncos' ease of navigating swift urbanization. Beyond habitat loss, window collisions kill thousands of birds across the spectrum, especially in low-rise urban areas like in Westwood, Di Liberto says. As ground dwellers in their nesting and feeding, juncos are also especially susceptible to feral cat predation, even at UCLA.

"The knowledge gap I'm trying to fill is, 'Are these shifts we observe in urban birds' behavior ecology actually mattering? Do changes in aggression or fear affect survival? And could these shifts be a factor impacting the juncos' ability to thrive in this novel environment?' I'm using long-term junco population at UCLA as a proxy for that," says Di Liberto, who can identify almost any banded junco through his binoculars, instantly recalling the name given to it by fellow and past Yeh lab members at time of capture. The close-knit group has exhausted most cheese-related names on the last batch of fledglings. They've now moved on to condiments and city names.

One of the season's wildest twists has been the success of one junco, a male named Brownie, who has built five nests dotting the windows of the northwest corner of the Court of Sciences. So far, three out of his four clutches have survived. His last clutch did hatch, but sadly the single surviving nestling was found dead in the nest - likely a result of the parents not having enough food to feed them at this time of year. If the nestling had survived a week longer and fledged, Di Liberto says Brownie and his mate would be the most successful breeding pair they've ever seen in the population of juncos at UCLA.

"Juncos are important because they're doing something that we want all birds to do: be persistent in cities, be able to adapt, multiply and have - assumingly - a positive impact on the environment," Di Liberto said. "They're a model of how we want, or hopefully can have, animals react to strong environmental change."

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