Heterospecific visual cues and trophic facilitation processes used by a solitary bone-eating vulture

While the influence of public information sharing on foraging strategies is of growing interest, empirical studies exploring intraguild social information use and facilitation roles between individuals with different trophic specializations remain scarce. We monitored 133 carcasses of different types/sizes in open and shrubland landscapes in the Spanish Pyrenees to explore bearded vulture foraging in relation to social information transfer and adaptive trophic behavior. We hypothesized that they might: 1) feed on carcasses after initial heterospecific exploitation; 2) use heterospecifics to locate and/or exploit carcasses; and 3) prefer old carcasses over fresh ones. We recorded bearded vultures scavenging at 44 carcasses; 95.5% had been previously exploited by heterospecifics (93.2% by griffon vultures <i>Gyps fulvus</i> and 2.3% by golden eagles <i>Aquila chrysaetos</i>) while only two small-sized carcasses were scavenged without previous heterospecific exploitation. Bearded vultures were not observed scavenging at carcasses used only by mammals. Both griffon and bearded vultures took longer to find carcasses in shrublands than in open landscapes. However, bearded vulture arrival times between landscapes after carcass discovery by griffon vultures were similar. Bearded vultures were more likely to discover a carcass the greater the number of griffon vultures exploiting it. Only 10.4% bearded vulture scavenging events occurred after the third week following heterospecific exploitation, suggesting that recently opened carcasses were preferred. Clearly, heterospecifics play an essential role in bearded vultures foraging success and griffon vultures are fundamental facilitators for specialist foragers, both in providing visual cues to food location and in opening up carcasses to enable access to food.

尽管公共信息共享对觅食策略的影响日益受到关注，但探索不同营养特化个体间的同营养级社群信息利用（intraguild social information use）与促进作用的实证研究仍较为匮乏。我们在西班牙比利牛斯山脉的开阔地带与灌丛景观中，对133具不同类型、大小的动物尸体开展监测，以探究胡兀鹫（bearded vulture）的觅食行为与社群信息传递、适应性营养行为之间的关联。我们提出以下三项假设：1）在异种动物首次利用动物尸体后，胡兀鹫再取食该尸体；2）借助异种个体来定位或利用动物尸体；3）相较于新鲜尸体，更偏好利用陈旧尸体。本次研究共记录到胡兀鹫在44具动物尸体上的食腐行为；其中95.5%的尸体此前已被异种动物利用（93.2%为高山兀鹫（griffon vulture，<i>Gyps fulvus</i>）利用，2.3%为金雕（<i>Aquila chrysaetos</i>）利用），仅2具小型尸体在未被异种动物预先利用的情况下被胡兀鹫取食。研究未观察到胡兀鹫在仅被哺乳类动物利用过的尸体上取食。高山兀鹫与胡兀鹫在灌丛景观中发现动物尸体的耗时均长于开阔地带。但当高山兀鹫已发现尸体后，胡兀鹫在两类景观中的抵达耗时并无显著差异。高山兀鹫利用该尸体的种群规模越大，胡兀鹫越有可能发现该尸体。仅有10.4%的胡兀鹫食腐行为发生在异种动物利用尸体后的第三周之后，这表明胡兀鹫更偏好刚被开启利用的尸体。综上可见，异种动物对胡兀鹫的觅食成功至关重要；高山兀鹫作为胡兀鹫这类特化觅食者的核心促进者，既能为胡兀鹫提供食物位置的视觉线索，也能通过撕开尸体为其创造取食通道。