In 1939, the accomplished author, doctor, and scientist Henry Smith Williams published a book called The Secret Life of Birds. Williams published over 100 books on a number of topics, so this one didn't necessarily stand out. But he had a keen eye, and even a few years before that he had published a paper on birds that made an intriguing claim.
Williams would lay out colored balls of yarn in his garden. He noticed that birds would take some of the yarn and use it to decorate their nests. But he made an even more interesting observation: the most popular color would change from season to season. He suggested that some of the birds pick up one color early on, and then that color becomes "trendy for other birds."
Fast forward 70 years, and no one paid any mind to this hypothesis. But in 2009, researchers from the University of Toulouse noticed that birds were incorporating the same type of plant into their nests, which also suggests a sense of fashion. In 2023, a new study now suggests the same thing.
Researchers led by Sally Vistalli essentially recreated the yarn experiment, but followed the birds more closely and noted everything the birds did carefully. The assumption was that since birds place such great emphasis on what their nests look like, it makes sense that they follow cultural trends.
"As an important determinant of reproductive success, avian nest building is under strong selection and requires behavioral plasticity to optimize conditions in which offspring develop. Learning is one form of plasticity that allows adaptation to the local environment," the team writes in the study.
They focused on tits -- blue, great, and marsh tits to be exact. The birds were studied in a woodland just outside of the Max Planck Institute for Behavioural Biology, in Radolfzell, Germany, where the researchers are based. The researchers tracked the birds using RFID yarn dispenser. Each dispenser contained two strands of two colors: either orange and pink or blue and purple. All the dispensers, however, were rigged to only dispense one of these in the beginning. Then, once one local nest was seen to include wool from a dispenser, the other color was also unlocked. The researchers also used a control in a separate area, where a similar system was deployed, but the yarn dispensers provided both colors right from the get-go. The idea was to see whether there was any difference between how the birds in the two groups behaved.
Overall, the tits in the research area built 68 nests that season and out of them 26 included wool from a dispenser. Among these, 18 were constructed after both colors were made available -- but 10/18 still only included the first color of wool chosen. Meanwhile, in the control area, 8 nests were made using wool, and all of them contained a mixture of colors.
Researchers note that this is a statistically significant difference and seems to back the idea that tits follow fashion trends, copying the behavior of the early influencers. Researchers suspect that it could be the elderly, more experienced birds that set the trend, and others follow them.
At any rate, it's not entirely clear why birds seem to practice this behavior, and there could be more
"Birds may refine nest-building behavior with personal experience or use social information to guide their choices. While there is mounting evidence for an effect of experience-based learning on nest building and social information use when selecting nesting material in the laboratory, experimental evidence for social information use in wild birds is lacking."
The study was published in the journal Behavioral Ecology and Sociobiology.