Rowland Institute, Harvard University, Cambridge, MA 02142.
Department of Mechanical Engineering, Seoul National University, Seoul 08826, Korea.
Proc Natl Acad Sci U S A. 2021 Jan 19;118(3). doi: 10.1073/pnas.2018509118.
Mud nests built by swallows (Hirundinidae) and phoebes () are stable granular piles attached to cliffs, walls, or ceilings. Although these birds have been observed to mix saliva with incohesive mud granules, how such biopolymer solutions provide the nest with sufficient strength to support the weight of the residents as well as its own remains elusive. Here, we elucidate the mechanism of strong granular cohesion by the viscoelastic paste of bird saliva through a combination of theoretical analysis and experimental measurements in both natural and artificial nests. Our mathematical model considering the mechanics of mud nest construction allows us to explain the biological observation that all mud-nesting bird species should be lightweight.
燕子（燕科）和食蚊鸟（霸鹟科）所筑的泥巢是附着在悬崖、墙壁或天花板上的稳定粒状堆。尽管人们观察到这些鸟类会将唾液与不粘的泥粒混合，但这些生物聚合物溶液如何为巢穴提供足够的强度来支撑居民的体重以及自身的重量仍然难以捉摸。在这里，我们通过在自然和人工巢穴中进行理论分析和实验测量，阐明了鸟类唾液粘弹性糊状物增强粒状团聚体的机制。我们的数学模型考虑了泥巢结构的力学，使我们能够解释这样一个生物学观察结果，即所有泥巢鸟类物种都应该是轻量级的。
