When the neighbourhood goes bad: can endangered black robins adjust nest site selection in response to the risk of an invasive predator? (#439)
In many birds, the risk of nest failure from predation is associated with characteristics of the nest site. Following nest predation it may therefore benefit the bird to select a nest site which reduces the risk of future loss to the same predator. We investigated nest-site selection following failed nesting attempts in an endangered endemic New Zealand passerine, the Chatham Island black robin Petroica traversi. Previous work has shown that almost all nest predation on robins is by introduced European starlings (Sturnus vulgaris) but that predation risk is reduced in low versus high nests, and in open versus cavity nests.We tested whether black robins (i) increase the distance between first and second nests when the first has been depredated, (ii) build replacement nests lower after predation, and (iii) are more likely to change nest substrate (cavity or open nests) following nest predation. We found that black robins built replacement nests at a greater distance from depredated first nests than from successful first nests, but they did not either nest lower or change nest substrates. This suggests that although black robins recognise nest failure due to predation, and respond by building replacement nests away from the area, they do not appear to link the predation event to particular nest site characteristics. In other species, the absence of systematic changes in nest site selection following predation has been attributed to diverse and unpredictable predator threats. Given evidence for the relative safety of particular nest site features in black robins, and the presence of a single predator type, this argument does not appear to explain the results of the current study. Instead, we suggest these findings may reflect predator naivety in black robins, which did not evolve with the predation risk posed by introduced starlings.