Functional connections between bird eggshell stiffness and nest characteristics through risk of egg collision in nests

• Published in: Ecology letters Vol. 25; no. 6; pp. 1421 - 1431
• Main Authors: Hung, Chih‐Ming, Tsao, Shu‐Han, Chiang, Pei‐Lin, Wu, Shang‐Ping, Tuanmu, Mao‐Ning, Juang, Jia‐Yang, Ruegg, Kristen
• Format: Journal Article
• Language: English
• Published: England Blackwell Publishing Ltd 01.06.2022; John Wiley and Sons Inc
• Subjects: Animals; avian evolution; Bird eggs; Birds; Birds - physiology; Body Temperature Regulation; Collision mortality; Ecological niches; Ecosystem; Egg Shell - physiology; Egg shells; Eggs; eggshell strength; Letter; Letters; nest attachment; nest site; nest structure; Nesting; Nesting Behavior - physiology; Nests; Niches; passerine; Predation; Risk; Stiffness; Thermoregulation; vegetation; nest site; avian evolution; passerine; nest attachment; nest structure; eggshell strength
• ISSN: 1461-023X; 1461-0248; 1461-0248
• DOI: 10.1111/ele.14001

Eggs and nests are two critical traits for the ecological success of birds. Their functional interactions, however, remain unclear. Here, we examined the functional connections between egg stiffness and nest attachment, site and structure for 1350 avian species. We revealed high eggshell stiffness for eggs in nests with a pensile attachment, located on non‐tree vegetation or having a domed shape, suggesting that birds produce stiffer eggs in response to higher egg‐collision risk in unstable or enclosed nests. Interdependence models suggested that the evolution of eggshell stiffness was more likely to be driven by than drive that of nest characters. Our results implied a trade‐off between investment in competing for established nesting niches and producing stiff eggs to explore novel niches with high collision risk, possibly mediated by predation or thermoregulation. This study highlights an overlooked connection between nests and eggshells that may have broadened the ecological niches of birds. This study establishes the form‐function connection between bird nests and eggs by examining the associations between eggshell stiffness and three nest characters for 1350 species. We provide empirical evidence that birds using unsteady or enclosed nests tend to produce eggs with high stiffness, revealing a long‐overlooked egg–nest interaction generated through the collision risk of eggs inside nests. The egg–nest interaction may also be associated with the evolution of birds and explain why birds can breed in diverse habitats.