Golden-crowned sparrows prefer familiar faces over familiar places

A recent study led by ecologists from the University of Nebraska–Lincoln reveals that golden-crowned sparrows may stray from their usual overwintering spot due to the absence of long-lasting flockmates. These friendly, familiar companions seem to anchor the sparrows to familiar spaces. The study found that when golden-crowned sparrows returned to California after a long winter migration of up to 3,000 miles, they resettled an average of just 90 feet from their previous year’s range center.

However, golden-crowned sparrows that appeared for at least their third consecutive winter began to move away from their preferred locations when their closest flockmates didn’t join them down south. This suggests that even for sparrows, the sense of home is tied to the company of familiar individuals.

Annie Madsen, the lead author and a recent Ph.D. graduate from Nebraska, explained that the study aimed to understand the intricate relationship between animals sharing territory and forming social bonds. Golden-crowned sparrows engage in fission-fusion networks, congregating in small groups before dispersing and reassembling with different flock members.

The challenge for ecologists is deciphering whether animals come together due to shared resources or social partnerships. Madsen pointed out the complex nature of this question and the difficulty in determining which factors truly influence their behavior.

The study aimed to determine whether sparrows are drawn to specific patches of territory or if their return is motivated by reuniting with their friends and flockmates.

The arboretum at the University of California, Santa Cruz, served as an ideal location to investigate the overwintering patterns of golden-crowned sparrows from Alaska and western Canada. Between 2009 and 2019, a team of researchers and volunteers utilized multicolored leg bands and diligent observation to map the sparrows’ geographic distribution and social networks.

Remarkably, as golden-crowned sparrows spent more consecutive winters in Santa Cruz, their average range shifted less from the previous year. This indicated a preference for certain sites, suggesting these spots might possess attractive features for the species.

However, the decade-long dataset also enabled the identification of each sparrow’s closest friends, representing the 10% of fellow sparrows most frequently spotted together in a given year.

An intriguing discovery emerged: a typical sparrow would lose around 52% of its favored flockmates across its migratory years to Santa Cruz. Interestingly, when the sparrow’s closest social contacts didn’t return in certain years, its home range shift reversed, moving farther from the previous center.

This led the researchers, including lead author Annie Madsen, to conclude that a sparrow’s loyalty wasn’t solely tied to a location and its resources, but also to the presence of expected feathered companions. This finding was significant, considering that resources are generally more abundant during overwintering than when seeking mates and raising offspring in the summer.

Annie Madsen, currently a postdoctoral researcher at the University of California, San Diego, noted the sparrows’ return to specific locations within the arboretum, despite the availability of plentiful food and comfortable surroundings. She suggested that social cohesion and familiarity with flockmates might be driving this behavior.

The researchers also made an intriguing observation: the loss of flockmates didn’t notably impact the home ranges of sparrows returning for only their second winter. This could indicate that these second-year sparrows hadn’t formed as many close bonds as those returning for multiple consecutive winters.

Madsen explained that relationships among sparrows develop over several years, with returning sparrows maintaining existing friendships while also forming new ones with returning and new flockmates. This accumulation of social capital over time contributes to their behavior.

The study’s findings were published in the Proceedings of the National Academy of Sciences.

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