Design principles of biologically fabricated avian nests

Abstract

Materials and construction methods of nests vary between bird species and at present, very little is known about the relationships between architecture and function in these structures. This study combines computational and experimental techniques to study the structural biology of nests fabricated by the edible nest swiftlet Aerodramus fuciphagus on vertical rock walls using threaded saliva. Utilizing its own saliva as a construction material allows the swiftlets full control over the structural features at a very high resolution in a process similar to additive manufacturing. It was hypothesized that the mechanical properties would vary between the structural regions of the nest (i.e. anchoring to the wall, center of the cup, and rim) mainly by means of architecture to offer structural support and bear the natural loads of birds and eggs. We generated numerical models of swiftlet nests from μCT scans based on collected swiftlet nests, which we loaded with a force of birds and eggs. This was done in order to study and assess the stress distribution that characterizes the specific nest’s architecture, evaluate its strength and weak points if any, as well as to understand the rationale and benefits that underlie this natural structure. We show that macro- and micro-scale structural patterns are identical in all nests, suggesting that their construction is governed by specific design principles. The nests’ response to applied loads of birds and eggs in finite element simulations suggests a mechanical overdesign strategy, which ensures the stresses experienced by its components in any loading scenario are actively minimized to be significantly smaller than the tensile fracture strength of the nests’ material. These findings highlight mechanical overdesign as a biological strategy for resilient, single-material constructions designed to protect eggs and hatchlings.

A modeling algorithm for exploring the architecture and construction of bird nests

“…The popularity of digital analyses may be due to many factors, from their ability to provide robust quantitative analyses for complex and intricate structures often found in biological systems, to the ability of numerical methods such as Computational fluid dynamics (CFD) and Finite element analysis (FEA) to provide colossal amounts of output data, allowing robust statistical analyses and detailed graphical displays. Digitized nest structures provides the opportunity to simulate and predict how a structure will perform under natural and extreme conditions, and investigate the effect of induced structural modifications on the natural function 28,34 .…”

“…Using non-destructive three-dimensional (3D) imaging techniques such as computer tomography (CT) provides the internal structure of the scanned objects for generating reliable volumetric models. Volumetric representations are particularly suitable for exploring the properties and behaviour of the objects under specific conditions, by means of computational manipulations, simulations, and analyses 31–34 . These structures may be 3D printed prior to generating digital manipulations to further explore the structure, e.g by means of mechanical testing 35 .…”

“…Digital analysis of the data and 3D models obtained from the actual biological structures provide us with a definitive description of the structures. Moreover, developing in-silico nest models based on actual nest structures has made it possible to perform various mechanical tests on the same structure and introduce structural modifications 34 .…”

“…To date, detailed description of construction patterns and materials used in avian nests are limited to only a few bird species 6,7,34 . This study improves our understanding of nest architectural designs exhibited by passerine birds by investigating the structure and its potential construction patterns.…”

A modeling algorithm for exploring the architecture and construction of bird nests

“…While such macro-scale biological structures cannot be studied by traditional biological tools, their structure-function relationships can be studied in-silico in digital formats. Digitizing complex structures by converting the objects using three dimensional (3D) imaging techniques, such as 3D scanning, computer tomography (CT), and magnetic resonance imaging (MRI) into numerical (digital) model representations, enables to explore their properties and behaviour under specific conditions, by means of computational manipulations, simulations, and analyses 5–8 . These structures may be 3D printed prior to generating digital manipulations to further explore the structure, e.g by means of mechanical testing 9 .…”