House martins respond to perceived danger

We designed a field experiment on breeding house martins (Delichon urbica) which build conspicuous nests in human structures, which require the parents to be wary of potential predators. Some birds therefore avoid entering the nest in the presence of a potential nest predator when the parent is most vulnerable when inside the nest. Therefore, the hesitation to enter the nest in the presence of a potential predator might be for the bird’s own safety. A number of species show such a hesitation in response to a human observer. Using this behaviour exhibited by the house martin, we show here that the bird appreciates the perspective of the observer and behaves as if it can understand what the observer ‘knows’.