Elevational differences in territory defence response in native (endemic and non-endemic) forest birds on Viti Levu Island, Fiji

Experimental approaches to measure territory defence can be used to interpret the relative magnitude of intraspecific aggression in different ecological contexts. The aim of this study is to examine the response of Fijian forest bird species to conspecific intruders using playback of previously recorded songs along an elevational gradient. We address two questions: Do different foraging guilds in Fiji’s forest birds show different patterns of territorial defence behaviour towards conspecific intruders? Secondly, do Fiji’s forest birds show stronger territorial defence at higher elevations? We explore these questions across two foraging guilds (insectivore and omnivore) on Viti Levu Island, Fiji. All four focal species had a stronger response at the highest elevation, and the endemic insectivore had the strongest response. Perhaps high elevation insects are less abundant and hence increased aggressiveness is favoured to defend the territory, and/or perhaps in general more aggressive birds colonise higher elevation areas, both ideas that require further testing. This study provides first insights into response to conspecifics in Fiji’s forest birds that can be explored in relation to avian behaviour also in the context of human activity, human disturbance and threats to the persistence of birds across elevational gradients.

本研究旨在探讨斐济森林鸟类对同种入侵者的响应，通过在海拔梯度上回放预先录制的歌声，以测量领土防御的实验方法来解释不同生态背景下种内攻击性的相对强度。研究旨在解决两个问题：斐济森林鸟类的不同觅食群体（食虫鸟和杂食鸟）对同种入侵者的领土防御行为是否表现出不同的模式？其次，斐济森林鸟类在较高海拔地区是否显示出更强的领土防御能力？本研究在斐济维提岛的两个觅食群体（食虫鸟和杂食鸟）中进行了探索。所有四种研究对象在最高海拔处均表现出更强的响应，而特有食虫鸟的响应最为强烈。或许高海拔地区的昆虫数量较少，因此增加攻击性以防御领土是有利的，或者可能是一般而言，更具攻击性的鸟类倾向于栖息于较高海拔地区，这两种假设均需进一步验证。本研究首次揭示了斐济森林鸟类对同种入侵者的响应，这些发现可以与鸟类行为学以及人类活动、人类干扰和鸟类在海拔梯度上持久性威胁的背景下进行探讨。