Leader N, Yom-tov Y
Department of Zoology, Tel-Aviv University
Anim Behav. 1998 Jul;56(1):207-17. doi: 10.1006/anbe.1998.0766.
Blackstarts, Cercomela melanura, Turdidae, construct a rampart of stones at the entrance to their nests. These ramparts may reach remarkable proportions, containing hundreds of flat rocks. We investigated several hypotheses regarding the function of stone ramparts, by monitoring individually marked blackstarts at the En-Gedi Nature Reserve, Israel. Stones were collected solely by females, who carried them in their beaks, while flying to the nest, at a rate of up to one stone per min, after pair formation had occurred. The number and total weight of stones as well as rampart height showed a highly positive correlation with the size of the nest cavity opening. The rampart decreased the size of the cavity entrance to some nests by as much as 67%, which suggests an antipredator barrier function. Survival rates of eggs and chicks were extremely low and the major cause of reproductive failure was predation. Successful nests tended to be located higher off the ground than predated nests, and often contained fewer stones. Furthermore, larger females in terms of wing and tail length nested in cavities higher off the ground and built smaller ramparts containing lighter stones. An artificial nest predation experiment did not reveal a difference in predation rates between nests with and without stone ramparts. Spiny mice, Acomys sp., were the main egg predators. However, in 37% of nests with ramparts that were predated, the perpetrator flattened the rampart, suggesting that they may serve as a barricade, forcing the predator to invest time in clearing the stones in order to gain access to the nest, and perhaps allowing the nesting female sufficient time to escape. We propose, therefore, that owing to such high nest predation rates, females nesting close to the ground build stone ramparts as an 'early warning' mechanism to prevent themselves from being trapped inside nest cavities and predated. Copyright 1998 The Association for the Study of Animal Behaviour.
黑尾鸲（Cercomela melanura，鸫科）在其巢穴入口处用石头筑起一道壁垒。这些壁垒规模惊人，包含数百块扁平的石头。我们通过在以色列恩盖迪自然保护区对个体做了标记的黑尾鸲进行监测，研究了关于石头壁垒功能的几种假说。石头完全由雌性收集，它们在配对后飞向巢穴时，用喙叼着石头，速度可达每分钟一块。石头的数量、总重量以及壁垒高度与巢洞开口大小呈高度正相关。壁垒使一些巢穴的洞口尺寸缩小了多达67%，这表明其具有反捕食屏障功能。卵和雏鸟的存活率极低，繁殖失败的主要原因是被捕食。成功筑巢的位置往往比被捕食的巢穴离地面更高，且通常石头较少。此外，翅膀和尾巴较长的较大雌性会在离地面较高的洞穴中筑巢，并建造较小的、包含较轻石头的壁垒。一项人工巢穴捕食实验并未揭示有石头壁垒和没有石头壁垒的巢穴在捕食率上的差异。刺巢鼠（Acomys sp.）是主要的卵捕食者。然而，在37%有壁垒但被捕食的巢穴中，捕食者会把壁垒弄平，这表明壁垒可能起到路障的作用，迫使捕食者投入时间清理石头以便进入巢穴，也许能让正在筑巢的雌性有足够的时间逃脱。因此，我们认为，由于如此高的巢穴捕食率，在靠近地面筑巢的雌性会建造石头壁垒作为一种“预警”机制，以防止自己被困在巢洞中并被捕食。版权所有1998动物行为研究协会。
