The blue rollers then behaved much more cautiously, report spanish researchers in the "biology letters" of the british royal society. Blue rollers (coracias garrulus), also known as almond crows, can hardly be confused thanks to their turquoise-blue plumage. Hollow broods are found mainly in southern and southeastern europe, but also in north africa and asia.
The team led by deseada parejo from the CSIC-EEZA research institute in almeria first discovered that blue jays spit out an orange liquid when they are placed in their nesting box. The substance may deter predators with its disgusting taste, researchers speculate in "biology letters". This still has to be investigated – but it has already been proven that the "spit" serves as a warning signal to the parents.
The scientists had painted the inside of nine nest boxes with chicks, the oldest of which was ten days old in each case, with one milliliter of the spitted fluid. The behavior of the bird’s parents was filmed and evaluated before and after each of the events. The bluebirds flew to the nests smelling of vomit and were more cautious in feeding the chicks. Nests smeared with lemon essence for comparison showed no such effect.
The results are further proof that the sense of smell is also important in birds, the researchers write. The "smell of fear" is an important signal in many animal species and also in humans, who begin to sweat profusely when they are in danger. Not only mammals, but also insects emit special substances when in danger. Ice petrels (fulmarus glacialis) are known to defend themselves against nest robbers by spitting an oily substance from their stomachs at them.