狼來啦!小型鳥類如何利用擬態警戒音對抗大型捕食者

褐刺嘴鶯 (Acanthiza pusilla)
photo: Brown thornibill (wiki)
標題:Crying wolf to a predator: deceptive vocal mimicry by a bird protecting young

摘要

Animals often mimic dangerous or toxic species to deter predators; however, mimicry of such species may not always be possible and mimicry of benign species seems unlikely to confer anti-predator benefits.We reveal a system in which a bird mimics the alarm calls of harmless species to fool a predator 40 times its size and protect its offspring against attack. Our experiments revealed that brown thornbills (Acanthiza pusilla) mimic a chorus of other species’ aerial alarm calls, a cue of an Accipiter hawk in flight, when predators attack their nest. The absence of any flying predators in this context implies that these alarms convey deceptive information about the type of danger present. Experiments on the primary nest predators of thornbills, pied currawongs (Strepera graculina), revealed that the predators treat these alarms as if they themselves are threatened by flying hawks, either by scanning the sky for danger or fleeing, confirming a deceptive function. In turn, these distractions delay attack and provide thornbill nestlings with an opportunity to escape. This sophisticated defence strategy exploits the complex web of interactions among multiple species across several trophic levels, and in particular exploits a predator’s ability to eavesdrop on and respond appropriately to heterospecific alarm calls. Our findings demonstrate that prey can fool predators by deceptively mimicking alarm calls of harmless species, suggesting that defensive mimicry could be more widespread because of indirect effects on predators within a web of eavesdropping.

這是個有意思的故事,述說如何以小蝦米對大鯨魚。

思考一下,一個體型較小的生物如何對抗捕食者?要不是逃走,要不是對抗,但如何對抗是個很大的問題,是要直接衝上去打一架?打不贏怎麼辦?或有其他的方法?
斑噪鍾雀 (Strepera graculina)
photo: Pied currawong (wiki)
黃翅澳蜜鳥 (Phylidonyris novaehollandiae)
photo: New Holland Honeyeater (wiki)

褐刺嘴鶯 (brown thornbills, Acanthiza pusilla) 是一種分佈於澳洲的小型鳥類 (約6克重),而大褐刺嘴鶯40倍的斑噪鍾雀(pied currawongs, Strepera graculina)會接近他們的巢攻擊,此時這種鳥會發出明顯是擬態黃翅澳蜜鳥 (New Holland honeyeater, Phylidonyris novaehollandiae)的警戒聲欺騙斑噪鍾雀以躲避攻擊,但實際上是如何運作的還是個謎。

Fig. 1 涉入物種間的生態闗係與警戒音
Fig. 2 不同處理下發出警戒音的次數
作者群有個複雜的假設:褐刺嘴鶯的警戒聲擬態是為了告訴捕食者有其他更高階的捕食者來了。作者群的實設有三個處理:以共棲的深紅玫瑰鸚鵡 (crimson rosella, Platycercus elegans) 做為無威脅的控制組、靠近巢的斑噪鍾雀為潛在威脅組,攻擊中的捕食者為立即威脅組,分別分析其發出的警戒音。研究結果顯示褐刺嘴鶯能發出類似黃翅澳蜜鳥頻率的警戒音,有效的欺騙捕食者(斑噪鍾雀),而這個警戒音是黃翅澳蜜鳥用以通知同類有空中捕食者。

總結這個故事其實是這樣:褐刺嘴鶯受到威脅後,發出黃翅澳蜜鳥的警戒音,恫嚇斑噪鍾雀「有捕食者在後面」,降低其攻擊的意願,此時褐刺嘴鶯藉著空檔逃走,就像「狼來了」以一樣。鳥類聲音的擬態牽涉高度認知科學。原使用者的警戒音要能夠忠誠反應其訊號(高階捕食者來了);捕食者要知道這個訊號代表的意義,;擬態者要認出捕食者,還要能選擇正確的警戒音(選錯就GG),這與被動的接受天擇的擬態形式以及機制的來源是有所差異。

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