Blue tits learn to avoid gross food by watching videos of other birds

Blue titmice and chickadees can learn to avoid unpleasant foods without even tasting them. Seeing another bird's disgusted response, even if only on video, helps them avoid unpleasant prey by recognizing their marks.

Chickadees learn to avoid unpleasant foods
Liisa Hämäläinen of Cambridge University and her colleagues have studied this type of social learning in blue titmice (Cyanistes caeruleus) and coal titmice (Parus major), who feed together.

Two groups of 24 birds, including 12 blue titmice and 12 sable titmice, were shown to eat unpleasant "prey" - food soaked in a bitter solution and marked with a black square - from two groups. The filmed birds reacted with disgust by wiping their beaks and shaking their heads.

The birds that watched the videos were then introduced to unpleasant food and their normal, unmodified food to see if they had learned from the filmed birds. Another set of 12 blue titmice and 12 coal titmice were introduced to these feeding options without watching the videos.

Even while watching a video 
For both species, the birds that watched the videos ate less unpleasant prey than those that did not. The blue titmice learned best by watching their own species, but the chickadees learned just as well by watching both species.

While it has been shown that many birds avoid certain prey by observing their own species, this has only been observed once before between these species; red-winged blackbirds (Agelaius phoeniceus) and common grackles (Quiscalus quiscula).

It is also the first time that blue titmice have used social information in the same way as sable titmice. Researchers believe this may be because this study focused on risky food choices.

"The two species are different in size, and it is possible that the coal titmice may be able to cope better with chemical defences because they are larger than the blue titmice," says Hämäläinen. "The costs of consuming potentially toxic food could therefore be higher in blue titmice."

Prey with more visible signals
Predators learning from each other in this way could explain why some prey develop visible marks despite the attention they attract. In places where several predators can learn from just one other bird, this could make warning signs more visible if it is worthwhile.