Data from: Evidence for facilitation among avian army-ant attendants: specialization and species associations across elevations

Mixed-species assemblages can involve positive and negative interactions, but uncertainty about high-value patchy resources can increase the value of information sharing among heterospecific co-foragers. I sampled species composition of bird-flocks attending army-ant raids in three adjacent elevation zones in Costa Rica, across multiple years, to test for positive and negative associations among raid-attending bird species. My goal was to test whether the most frequent and specialized raid-attending species showed evidence of facilitating or excluding other bird species. I quantified elevational variation in avian community composition at raids, then asked whether species composition was associated with variation in flock characteristics (flock size and species richness). I identified the most frequent raid-attending species (those that attended raids most frequently relative to their mist-net capture rates), and bird species that performed specialized army ant-following behavior (bivouac-checking, which allows birds to memorize and track mobile army-ant colonies). There was significant turnover of bird species among zones (including the frequent and specialized attendants); patterns of species overlap suggested a gradual transition from a Pacific-slope to an Atlantic-slope raid-attending bird fauna. Raid-attendance frequency was positively correlated with bivouac-checking behavior. With few exceptions, the most frequent raid-attending bird species, and the bivouac-checking species, also participated in the most species-rich flocks. High species-gregariousness suggests many of the frequently attending and/or bivouac-checking species functioned as core flock members. However, some bird species pairs were significantly negatively associated at raids. Despite species turnover, per-flock numbers of birds at raids did not differ among geographic zones, but flocks on the Pacific-slope were heavier because larger bodied bird species attended raids. Previous studies showed that the size (biomass) of bird-flocks corresponds to the amount of food the birds kleptoparasitize from ant raids, and the heavier Pacific-slope bird-flocks could have greater negative kleptoparasitic impacts.混合物种种群（mixed-species assemblages）可存在正向与负向相互作用，但针对高价值斑块性资源的信息不确定性，反而会提升异种共觅食者间共享信息的收益。本研究于多年间在哥斯达黎加的三个相邻海拔带中，对参与军蚁觅食突袭（army-ant raids）的鸟群物种组成开展采样，以检验参与蚁群突袭活动的鸟类物种间的正向与负向关联。本研究旨在验证：出现频率最高且特化于跟随蚁群活动的鸟类物种，是否表现出促进或排斥其他鸟类物种的证据。本研究量化了蚁群突袭活动中鸟类群落组成的海拔差异，并探究物种组成是否与鸟群特征（鸟群规模与物种丰富度）存在关联。本研究鉴定出两类物种：一是出现频率最高的跟随蚁群活动的鸟类物种（即相对于雾网（mist-net）捕获率而言，参与蚁群突袭活动频率最高的物种）；二是表现出特化军蚁跟随行为（army ant-following behavior）的鸟类物种——蚁穴巡查行为（bivouac-checking），该行为可帮助鸟类记忆并追踪移动中的军蚁集群。不同海拔带的鸟类物种存在显著更替（包括高频跟随蚁群的物种与特化跟随物种）；物种重叠模式显示，跟随蚁群活动的鸟类区系从太平洋坡向大西洋坡呈现逐步过渡的特征。参与蚁群突袭的频率与蚁穴巡查行为呈显著正相关。除极少数例外情况外，高频参与蚁群突袭的鸟类物种与蚁穴巡查物种，同样会出现在物种最丰富的鸟群中。较高的物种群聚性表明，多数高频跟随蚁群活动和/或表现出蚁穴巡查行为的物种，充当了鸟群核心成员的角色。但部分鸟类物种对在蚁群突袭活动中呈现显著负关联。尽管存在物种更替，不同地理带的鸟群个体总数并无显著差异；然而太平洋坡的鸟群生物量更高，这是因为体型更大的鸟类参与了蚁群突袭活动。既往研究表明，鸟群的规模（生物量）与鸟类从蚁群突袭活动中盗食寄生（kleptoparasitize）获得的食物量呈正相关；因此太平洋坡的高生物量鸟群，可能会对蚁群产生更强的负向盗食寄生影响。