Analyze This: Birds may decorate nests to scare off rivals

Feathers can make nests look like a kill site where birds don’t want to be caught dead

Blue tits, a species of bird, make their nests inside hollows like the one seen here. Competition for those spaces can be fierce. So some birds try to scare off competitors by making their nests look like another bird had died there, a new study finds.

Natalia Bubochkina/iStock/Getty Images Plus

Some birds are interior decorators, placing big, showy feathers in their nests. But rather than spiffing up their homes, these birds may be trying to spook nest-stealing neighbors.

Karen Wiebe is a behavioral ecologist. She studies animal behavior and ecosystems at the University of Saskatchewan in Saskatoon, Canada. Birds sometimes weave feathers into their nests to provide insulation. But Wiebe and her colleague, Tore Slagsvold of the University of Oslo in Norway, also saw birds placing large feathers on the surfaces of nests. Those feathers wouldn’t help with warmth. The researchers wondered whether the birds might be using the decorations to send a message.

For swallows and other birds that nest in holes and hollows, competition for nests can “be really ferocious,” Wiebe says. Birds scream, grapple and peck, sometimes killing an opponent. But these somewhat scarce holes can also hide danger. Owls, weasels or other predators may be lurking inside. If a nest contains feathers or other remains, it might be evidence that a predator had been there. Those holes might not be as desirable.

a photo taken looking down into the nest of a blue tit bird, there are several large feathers strewn about
This female blue tit decorated her nest with feathers. That makes it look a dangerous spot where a predator may have killed another bird.T. Slagsvold and K.L. Wiebe/Royal Society Open Science 2021 (CC BY 4.0)

Wiebe and Slagsvold hypothesized that some birds may use feathers to create a mock kill site. Their goal: Scare competitors away.

During spring, when nest competition is fiercest, the scientists set up pairs of nesting boxes. One box contained white feathers. The other either contained no feathers or black feathers. Inside the boxes, black feathers were more difficult to see than white ones. Using video cameras, the researchers spied on how tree swallows, blue tits and pied flycatchers reacted to the boxes. They watched how long birds waited to explore a nest box. When birds took longer to enter, that suggested the animals were scared.

Birds of all three species hesitated to enter boxes with white feathers. But when feathers were in front of a nest, birds hopped right up and grabbed them. That suggested that birds weren’t afraid of the feathers themselves. The scientists shared their findings November 21 in Royal Society Open Science.

“It was really interesting to discover that birds were using a deceptive trick to help them keep their nests,” Wiebe says. When a bird leaves its nest to search for food, that opens the door for a nest stealer. “But if it can buy a little time by scaring away intruders with these feathers, then it has a better chance of coming back in time to defend its nest site.”

Data Dive:

  1. Which birds took the shortest time to enter the nests?
  2. Which birds took the longest time?
  3. What is the range of time it took birds to enter a nest with white feathers?
  4. What is the range of time it took birds to enter a nest with black feathers?
  5. How did the time for birds to enter a nest with black feathers compare with no feathers?
  6. What are some other items birds may be afraid to find in nests?
  7. The scientists also tested if birds were afraid of the white feathers because they were white. How could you design an experiment to test if birds are afraid of white objects?

Carolyn Wilke is a former staff writer at Science News for Students. She has a Ph.D. in environmental engineering. Carolyn enjoys writing about chemistry, microbes and the environment. She also loves playing with her cat.

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