Filek Nikolaus, Cimadom Arno, Schulze Christian H, Jäger Heinke, Tebbich Sabine
1Department of Behavioural Biology, University of Vienna, Althanstrasse 14, 1090 Vienna, Austria.
2Department of Botany and Biodiversity Research, University of Vienna, Rennweg 14, 1030 Vienna, Austria.
J Ornithol. 2018;159(1):129-140. doi: 10.1007/s10336-017-1481-4. Epub 2017 Aug 8.
In recent decades, arboreal Darwin's Finches have suffered from a dramatic population decline, which has been attributed to parasitism by the invasive botfly . However, changes to their primary habitat caused by invasive plant species may have additionally contributed to the observed population decline. The humid cloud forest on Santa Cruz Island is a stronghold of arboreal Darwin's Finches but has been invaded by blackberry (). In some areas, manual control and herbicide application are used to combat this invasion, both causing a temporary removal of the entire understory. We hypothesized that the removal of the understory reduces the availability of arthropods, which are a main food source during chick rearing. We compared the foraging behaviour of Warbler Finches () and Small Tree Finches () at three study sites that varied in the degree of invasion and the length of time since the last herbicide application. We used prey attack rate and foraging success as an index for food availability and predicted a lower attack rate and foraging success in areas that had recently been sprayed with herbicides. We found that both the invasion and the management of influenced microhabitat use, foraging substrate and prey choice in both species. Contrary to our hypothesis, we did not find a lower attack rate or foraging success in the area with recent herbicide application. This may be explained by the finding that both species mainly foraged in the canopy but also used dead plant structures of the understory of the recently controlled area that resulted from the invasive plant management.
近几十年来，树栖达尔文雀的数量急剧下降，这被归因于入侵性肤蝇的寄生。然而，入侵植物物种对其主要栖息地的改变可能也导致了观察到的数量下降。圣克鲁斯岛上的潮湿云雾森林是树栖达尔文雀的一个据点，但已被黑莓入侵。在一些地区，人工控制和除草剂的使用被用来对抗这种入侵，这两者都会导致整个林下植被暂时消失。我们假设林下植被的消失减少了节肢动物的可获得性，而节肢动物是雏鸟饲养期间的主要食物来源。我们比较了莺雀和小树雀在三个研究地点的觅食行为，这三个地点在黑莓入侵程度和上次使用除草剂后的时间长度方面各不相同。我们将猎物攻击率和觅食成功率作为食物可获得性的指标，并预测在最近喷洒过除草剂的地区攻击率和觅食成功率会更低。我们发现，黑莓的入侵和管理都影响了这两个物种的微生境利用、觅食基质和猎物选择。与我们的假设相反，我们没有发现在最近喷洒过除草剂的地区攻击率或觅食成功率更低。这可能是因为发现这两个物种主要在树冠层觅食，但也利用了入侵植物管理导致的最近控制区域林下植被的枯死植物结构。
