Do hair-crested drongos reduce prospective territory competition by dismantling their nest after breeding?

Animals that breed seasonally often use the same territory where they successfully produced young previously. Intra-specific competition may be intense for these high-quality territories, and therefore, natural selection should favour behaviour of territory owners to reduce such competition. Hair-crested drongos, Dicrurus hottentottus, a territory-faithful migratory passerine, dismantle their nests after breeding. As undismantled nests usually remain intact until the next breeding season, we hypothesised that nest dismantling serves the purpose of reducing territory competition from conspecifics that may use the presence of a nest as a cue to select suitable territories in the next year. Here, we provide the first experimental test of this "territory competition hypothesis". Our results show that successful pairs, who often reuse their territories in the next year, were more likely to dismantle their nests and tended to dismantle faster compared to failed breeding pairs who often moved to another territory in the next year. Strengthened natural nests that were experimentally placed in successful territories attracted prospectors. However, the usurpation rate of those territories in the following year was low and not higher than that of territories where nests were dismantled. Furthermore, returned strengthened-nest owners did not initiate breeding later or produce fewer fledglings suggesting that potential higher territory competition did not affect their reproduction. Altogether, our results only partially support the "territory competition hypothesis". We suggest that nest dismantling may only be beneficial to drongos in years when territory competition is very intense.Significance statementSeasonal-breeding animals may face intra-specific competition for high-quality territories. Successful individuals often reuse their territory, but whether they can reduce prospective territory competition through hiding breeding locations (e.g. nests) has rarely been studied. We conducted an experiment to test whether a medium-sized passerine reduces the potential costs of territory competition by destroying their nest after breeding, concealing their selection of territory to other individuals. Territory owners invested more in nest dismantling if they were more likely to reuse the territory. However, they were still able to retain their previous territory and did not have a lower reproductive success if their nest was not dismantled. We suggest that individuals may only benefit from masking public information of breeding habitat selection from conspecifics by dismantling their nest when territory competition is very intense.