Avian nest abandonment prior to laying—a strategy to minimize predation risk?

Nest abandonment prior to laying is poorly understood and rarely studied. One possible explanation is that it is a behavior which may have evolved in response to high predation risk in nesting birds as a strategy to avoid the even greater costs of losing eggs or chicks. We tested this hypothesis in the Grey Fantail (Rhipidura albiscapa), a species that builds and abandons multiple nests throughout its breeding season without laying eggs. We placed artificial nests (that contained natural and plasticine eggs) in the exact locations of natural nests from the previous breeding season (spanning a large elevational gradient) for which the fate was known (abandoned, predated, or fledged). Trials were conducted early and late in the breeding season to test for temporal patterns. We postulated that should nest abandonment indeed reduce predation risk, then artificial nests placed at previously abandoned nest sites should have a greater risk of predation than nests placed at predated or fledged nest sites. Overall, we found that 74% of artificial nests were predated, with predation attributed to birds (66%), small mammals (7%), ants (8%), and unknown predators (19%). Artificial nest predation varied according to previous nest fate, whereby predation rates were lowest for predated sites, slightly higher for fledged, and highest at previously abandoned nest sites. In addition, cover increased survival rates for all nest site types. However, we observed a shift in the proportion of nests predated by birds versus other predator taxa, whereby nest predation by birds was highest late in the season at high elevation; this increase may have been due to extreme high temperatures at low elevation resulting in bird predators moving to refuges at higher elevation.