Functional morphology of the cranio‐mandibular complex of the Guira cuckoo (Aves)

Abstract

The cranio-mandibular complex is an important structure involved in food capture and processing. Its morphology is related to the nature of the food item. Jaw muscles enable the motion of this complex and their study is essential for functional and evolutionary analysis. The present study compares available behavioral and dietary data obtained from the literature with novel results from functional morphological analyses of the cranio-mandibular complex of the Guira cuckoo (Guira guira) to understand its relationship with the zoophagous trophic habit of this species. The bite force was estimated based on muscle dissections, measurements of the physiological cross-sectional area, and biomechanical modeling of the skull. The results were compared with the available functional morphological data for other birds. The standardized bite force of G. guira is higher than predicted for exclusively zoophagous birds, but lower than for granivorous and/or omnivorous birds. Guira guira possesses the generalized jaw muscular system of neognathous birds, but some features can be related to its trophic habit. The external adductor muscles act mainly during food item processing and multiple aspects of this muscle group are interpreted to increase bite force, that is, their high values of muscle mass, their mechanical advantage (MA), and their perpendicular orientation when the beak is closed. The m. depressor mandibulae and the m. pterygoideus dorsalis et ventralis are interpreted to prioritize speed of action (low MA values), being most important during prey capture. The supposed ecological significance of these traits is the potential to widen the range of prey size that can be processed and the possibility of rapidly capturing agile prey through changes in the leverage of the muscles involved in opening and closing of the bill. This contributes to the trophic versatility of the species and its ability to thrive in different habitats, including urban areas.

A low‐cost, easy‐to‐build, and portable bite‐force transducer for birds

“…Determining in vivo bite forces is important for studies of the mechanical output of the jaw system of birds, and complements the results of other studies that predict jaw muscle bite forces and the stress/strain distributions of the craniomandibular complex (e.g., Soons et al 2010, Sustaita andHertel 2010). Some investigators have examined theoretical bite forces of birds based on muscle dissections, calculation of physiological cross-sectional area of adductor muscles, and skull biomechanical modeling (i.e., Sustaita 2008, Carril et al 2015, Pestoni et al 2018, or by using finite element analysis as a tool to predict bite force (Degrange et al 2010, Soons et al 2010). However, these models usually do not incorporate all the details of complex natural systems that can influence avian bite forces, e.g., the presence of a rhamphotheca and cranial kinesis.…”

“…2015, Pestoni et al. 2018), or by using finite element analysis as a tool to predict bite force (Degrange et al. 2010, Soons et al.…”

Inter‐relationships among body mass, jaw musculature and bite force in birds

“…For a given body mass, the smaller passerines in this study have more jaw muscle mass and so generate more bite force than non-passerines. This pattern may reflect the feeding strategies of the species studied because insectivores and zoophagous birds have lower bite forces (Pestoni et al, 2018). However, the dataset had many values for finches and other granivorous species that feed on seeds, which require force to de-husk them and so gain access to the nutritious kernels (van der Meij & Bout, 2004, 2006.…”

“…There are also reports for bite forces have also been determined from the characteristics of the jaw musculature (e.g. Carril et al, 2015;Pestoni et al, 2018). Other studies have modelled bite force using finite element analysis (FEA; Soons et al, 2012Soons et al, , 2015To et al, 2021).…”

Why the long beak? Phylogeny, convergence, feeding ecology, and evolutionary allometry shaped the skull of the Giant Cowbird Molothrus oryzivorus (Icteridae)

“…Within the craniomandibular complex, we focused on the anatomy of the upper jaw, since the Giant Cowbird is at a glance highly distinctive from its congeners in its morphology (Mann, 2017; Ortega, 1998). In addition, they represent a functional morphological complex of undeniable ecological significance (e.g., Beecher, 1962; Pestoni et al, 2018; Richards & Bock, 1973) that is amenable to study from skeletal data under a comparative framework. Particular attention was given to upper jaw proportions and the morphology of the distinctive bony casque of icterids, which is greatly developed in the Giant Cowbird and in caciques and oropendolas, as has previously been emphasized (Beecher, 1951; Webster, 2003).…”