Steinfield, Ok.R., Felice, R.N., Kirchner, M.E. and Knapp, A. (2024). Carrion converging: Cranium form predicts feeding ecology in vultures. Journal of Zoology, vol. 322, pp. 113-125. https://doi.org/10.1111/jzo.13127
Claiming a relationship between cranium morphology and feeding ecology in birds may look like a manifestly apparent assertion. Scientists have been investigating the evolution of fowl skulls in relation to weight-reduction plan since Darwin’s finches. Nevertheless, methodological developments in morphology have forged doubt on this basic form-function relationship. Each throughout broad taxonomic samples and inside extra restricted teams, weight-reduction plan has insufficiently defined cranium form, highlighting elements akin to allometry (the connection between measurement and form) and phylogeny as being extra vital contributors to avian cranial evolution. There have been a number of hypotheses why: Maybe the taxonomic examine teams are too huge, the cranium/beak has too many different features, or dietary classes are simply too broad.
Vultures as an Preferrred Examine System
Vultures are a paraphyletic purposeful guild fashioned from members of two avian households: Afro-Eurasian vultures (Accipitridae) and American vultures (Cathartidae). Obligate scavenging, a foraging type distinctive to vultures amongst vertebrates, has developed independently in each households. One may then anticipate that cranium morphology would additionally converge due to extremely specialised meals necessities. Certainly, a 2016 examine on raptor cranial morphology discovered vultures to be the one group to exhibit traits on the premise of weight-reduction plan, whereas allometry defined the vast majority of cranium form variation throughout raptors as a complete.
Earlier analysis has recognized three distinct feeding methods in vultures as supported by behavioral observations and mirrored in cranium morphology: gulper, ripper, and scrapper (Desk 1). That is the primary examine to make use of three-dimensional geometric morphometrics to research the relative contributions of allometry, phylogeny, and feeding ecology on vulture cranium form.
Desk 1. Vulture Feeding Classification System.
| Feeding Kind | Food regimen | Mode of Feeding |
| Ripper | More durable materials, pores and skin/disguise, muscle, and tendons. Usually feed on the exterior areas of a carcass. | Sturdy tearing motion away from the carcass. |
| Gulper | Gentle tissue, and viscera. Usually feed on the interior materials of a carcass. | Full insertion of the top into the carcass for swallowing mushy meals. |
| Scrapper | Scraps of meat discovered across the carcass, usually the leftover materials of one other feeding scavenger. | Pecking movement to select up small scraps on the bottom and across the carcass. |
What did we discover?
The distinct form of vulture skulls in comparison with non-vulture raptors of comparable measurement and geographic vary, coupled with examples of convergence in form between vultures from each households, recommend that the distinctive feeding ecologies of vultures are appreciable drivers of vulture cranium evolution.
Regardless of the robust phylogenetic affect on cranium form, vultures cluster based mostly on feeding sort, occupying fully distinct areas of form area (Determine 1). Cranium form performs extraordinarily effectively on predicting feeding ecology and might separate vultures from different raptors, and phenotypic convergence inside every group is critical. Collectively, this means that adaptation to completely different feeding ecologies has pushed divergence in cranium form inside Accipitridae and Cathartidae.
Importantly, the outcomes of our examine spotlight the restrictions of predictions based mostly solely on morphology, and the necessity for supplementing morphometric information with behavioral observations.
The place can we go from right here?
The flexibility to foretell operate from type has been a contentious matter in fowl cranium morphometrics, and to take action utilizing a single purposeful trait has had blended outcomes (Pigot et al., 2020; Natale & Slater, 2022). As recommended by earlier analysis, utilizing extra detailed ecological context utilized to smaller purposeful guilds has improved predictive energy. “Scavenger” is a broad time period relevant to many opportunist and carnivorous species and inclusion underneath this umbrella time period has the potential to group collectively specialised (ecologically constrained) and generalist (ecologically versatile) taxa.
The evolution of vulture skulls underneath such specialised feeding ecology could possibly be of appreciable significance to vulture conservationists. Vultures are one of the endangered teams of birds on the planet (https://www.iucnvsg.org/) and vulture conservation initiatives usually contain the usage of artificially offered meals sources akin to supplementary feeding websites. These interventions ought to think about each the potential of morphological constraints for feeding in wild populations, in addition to potential evolutionary penalties of meals sources on captive inhabitants morphology.
Katherine Steinfield