Norwegian biologists uncover purpose behind birds decorating nests with unusual objects
New research finds that adding plastic or metal helps birds protect their eggs from clever predators like magpies and ravens
A team of Norwegian biologists has discovered that birds often add unusual objects, such as plastic or metal, to their nests for a critical reason: to protect their eggs from predators. In a recent study published in the Royal Society Open Science journal, researchers focused on how these decorative additions, sometimes odd or shiny, influence the likelihood of predation by magpies and ravens. They designed three types of artificial nests and conducted trials in both forested and dump site environments.
The experiments included 78 trials in forests and 60 at dump sites, offering nests with only eggs, nests with metal spoons nearby, and nests with large feathers near the eggs. Results showed that magpies raided plain nests after an average of 96 hours, but hesitated over 149 hours before approaching nests decorated with unusual materials. Ravens similarly waited longer to investigate or attack nests with added metal or feathers, indicating a strong deterrence effect.
Experts say this behavior reveals birds’ creative and adaptive strategies to defend their brood from savvy predators. The findings shed light on a key evolutionary tactic in Norway’s wild bird populations and suggest that birds have developed surprisingly effective ways to outsmart threats by making their nests appear unfamiliar or unsafe to would-be egg thieves.
