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Bird beaks in gen­eral did not adapt to food types as in Gala­pa­gos finches

pub­lished 27 Jan­u­ary 2019 | mod­i­fied 27 Jan­u­ary 2019

A recent study has shed some new light on how the beaks of birds have adapted over time.

puffins beak evolutionPic­tures depict­ing three dif­fer­ent tasks (dis­play, preen­ing and feed­ing) of the Atlantic puf­fin (Frater­cula arc­tica), one of the 176 bird species stud­ied in the arti­cle, accom­plishes with its beak.
Image credit: Pho­tographs were taken by Ser­gio Martínez-​Nebreda and Paula Medina-​García in Skomer Island in 2017 and 2018.

The obser­va­tion that Gala­pa­gos finch species pos­sessed dif­fer­ent beak shapes to obtain dif­fer­ent foods was cen­tral to the the­ory of evo­lu­tion by nat­ural selec­tion, and it has been assumed that this form-​function rela­tion­ship holds true across all species of bird. How­ever, a new study pub­lished on 8 Decem­ber 2018 in the jour­nal Evo­lu­tion sug­gests the beaks of birds are not as adapted to the food types they feed on as it is gen­er­ally believed.

An inter­na­tional team of sci­en­tists from the United King­dom, Spain and the US used com­pu­ta­tional and math­e­mat­i­cal tech­niques to bet­ter under­stand the con­nec­tion between beak shapes and func­tions in liv­ing birds. By mea­sur­ing beak shape in a wide range of mod­ern bird species from museum col­lec­tions and look­ing at infor­ma­tion about how the beak is used by dif­fer­ent species to eat dif­fer­ent foods, the team were able to assess the link between beak shape and feed­ing behaviour.

Pro­fes­sor Emily Ray­field, from the Uni­ver­sity of Bristol’s School of Earth Sci­ences, and senior author of the study, said: “This is, to our knowl­edge, the first approach to test a long-​standing prin­ci­ple in biol­ogy: that the beak shape and func­tion of birds is tightly linked to their feed­ing ecologies.”

The con­nec­tion between beak shapes and feed­ing ecol­ogy in birds was much weaker and more com­plex than we expected and that while there is def­i­nitely a rela­tion­ship there, many species with sim­i­larly shaped beaks for­age in entirely dif­fer­ent ways and on entirely dif­fer­ent kinds of food.

Guillermo Navalón, lead author, School of Earth Sci­ences, Uni­ver­sity of Bris­tol — United King­dom, and Unidad de Pale­on­tología, Depar­ta­mento de Biología, Uni­ver­si­dad Autónoma de Madrid — Spain.

bird beak evolutionOverview of the analy­sis and results from Navalón et al. (2019). Feed­ing ecol­ogy was divided into (A) diet classes and (B) food acqui­si­tion meth­ods, and their evo­lu­tion­ary cor­re­la­tion with two impor­tant char­ac­ter­is­tics of cra­nial mor­phol­ogy was tested: © the shape of the upper beak, and (E) the lever­age (or gear­ing) of the main jaw closer mus­cles by the lower beak, for which high mechan­i­cal advan­tages (to effi­ciently gen­er­ate high bite forces) are reached when the moment arm of the mus­cles’ input force is rel­a­tively high (E). These prop­er­ties were inferred from (D) lateral‐view pho­tographs of bird skulls.
Van Wassen­bergh and Baeck­ens, 2019.Digest: Evo­lu­tion of shape and lever­age of bird beaks reflects feed­ing ecol­ogy, but not as strongly as expected. In Evo­lu­tion — Free access.

This is some­thing that has been shown in other ani­mal groups, but in birds this rela­tion­ship was always assumed to be stronger,” Navalón added.

Co-​author, Dr Jesús Marugán-​Lobón from Uni­ver­si­dad Autónoma de Madrid, said: “These results only made sense when you realise birds use the beak for lit­er­ally every­thing! There­fore, also makes sense they evolved a ver­sa­tile tool not just for get­ting food, but also to accom­plish many other tasks.”

The study is part of a larger research effort by the team in col­lab­o­ra­tion with researchers from other uni­ver­si­ties across Europe and the US to bet­ter under­stand the main dri­vers of the evo­lu­tion of the skull in birds.

Dr Jen Bright, co-​author from the Uni­ver­sity of South Florida, said: “We have seen sim­i­lar results before in birds of prey, but this is the first time we stud­ied the link between beak shape and ecol­ogy across all bird groups. We looked at a huge range of beak shapes and feed­ing ecolo­gies: hum­ming­birds, eagles, par­rots, puffins, flamin­gos, pretty much every beak you can think of.”

Guillermo Navalón added: “These results have impor­tant impli­ca­tions for the study of fos­sil birds. We have to be care­ful about infer­ring ecol­ogy in ancient birds, which we often assume based solely on the shape of the beak. Really, we’re just start­ing to scratch the sur­face, and a lot more research is needed to fully under­stand the dri­vers behind beak shape evolution.”

(Source: Uni­ver­sity of Bris­tol press release, 22.01.2019)

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