Male Great Bowerbirds perform courtship display using a novel structure that rivals cannot destroy

Male–male competition can cause less competitive males to pursue alternative mating strategies or defer reproduction until they are older. For species that display using non-bodily ornaments, male interference can also involve limiting rivals’ access to display materials. I document a novel solution to male interference with external display structures in Great Bowerbirds (<i>Ptilonorhynchus nuchalis</i>). Males build and display at stick structures (‘bowers’), but they frequently destroy other males’ bowers. I show that some males, including young individuals, adapt to this interference by displaying around tree trunks instead of bowers. Tree trunks cannot be destroyed, so males can display at them despite interference. Display rates were higher at tree trunk display sites (‘display trees’) than bowers. Display trees had a basal diameter similar to the width of the front of the bower walls, allowing males to display in a similar manner as at bowers. Bower-owning males stole more experimentally placed decorations from display trees than random trees or bowers; most attempts at bower building by males at display trees were destroyed. Display trees were located closer to bowers than bowers were to each other. Display trees may allow younger and less competitive males to attempt to attract females visiting nearby established bowers and to gain competence in display.

雄性间竞争可导致竞争力较弱的雄性采取替代性交配策略，或是延迟繁殖直至年龄更大。对于依靠非身体装饰进行展示的物种而言，雄性间的干扰还可能包括限制竞争对手获取展示材料的途径。本文记录了大亭鸟（Great Bowerbird，<i>Ptilonorhynchus nuchalis</i>）应对雄性干扰其外部展示结构的一种全新策略。雄性会搭建枝条构筑的“亭巢”（bowers）并在此展示，但它们时常会破坏其他雄性的亭巢。研究显示，包括年轻个体在内的部分雄性会适应这类干扰行为，转而在树干周围开展展示，而非依赖亭巢。树干无法被破坏，因此即便存在这类干扰，雄性仍可在树干处进行展示。树干展示点（展示树，display trees）的展示频率高于亭巢。展示树的基部直径与亭巢壁正面的宽度相近，使得雄性能够以与在亭巢中相似的方式进行展示。拥有亭巢的雄性从展示树上盗取的人工放置装饰物品，多于从随机选取树木或亭巢中盗取的数量；而在展示树上尝试搭建亭巢的雄性，其搭建行为大多会被破坏。展示树的位置相较于亭巢之间的间距，更靠近已建立的亭巢。展示树或许能让年轻且竞争力较弱的雄性，得以尝试吸引到访附近已建成亭巢的雌性，并积累展示相关的经验与能力。