DOI: 10.5061/dryad.v15dv41z2
title: Data from: Diet, habitat, and flight characteristics correlate with intestine length in birds

description: It is often assumed that there is a link between diet and the dimensions
 of the avian intestinal tract. Typically, species that feed on
 hard-to-digest items have longer intestines, the opposite being true for
 species that consume highly digestible diets. However, few studies tested
 this hypothesis. Here, we collated data on the length of intestinal
 sections and body mass of 390 bird species and tested various
 relationships with diet, climate, and locomotion proxies. There was a
 strong phylogenetic signal in all datasets. The total and the small
 intestine scaled more than geometrically (95%CI of the scaling exponent
 excluding 0.33). The traditional dietary classification (faunivore,
 omnivore, herbivore) had no significant effect on total intestine length.
 Significant dietary proxies included %folivory, %frugi-nectarivory, and
 categories (frugi-nectarivory, granivory, folivory, omnivory, insectivory,
 and vertivory). Individual intestinal sections were affected by different
 dietary proxies. The model that best explained avian total intestine
 length included %frugi-nectarivory, habitat aridity, and degree of flight.
 Higher consumption of fruit and nectar, drier habitats, and a high degree
 of flightedness were linked to shorter total intestine length. However,
 the large intestine length was longer in species from drier habitats. This
 study corroborates the correlation between trophic niche and intestinal
 length only when using more detailed dietary proxies than those
 conventionally used in mammals. Notably, the length of the avian intestine
 depends on other biological factors as much as on diet. Given the weak
 dietary signal in our datasets, the diet-intestinal length relationships
 lend themselves rather to a narrative of flexibility (‘morphology is not
 destiny’) than of distinct adaptations that facilitate using one character
 (intestine length) as a proxy for another (diet). Generally, compared to
 mammals, birds have shorter intestinal sections, with a total intestine
 about 85% that of mammals of similar size.
description: # Data from: Diet, habitat, and flight characteristics correlate with
 intestine length in birds Dataset DOI:
 [10.5061/dryad.v15dv41z2](10.5061/dryad.v15dv41z2) ## Description of the
 data and file structure Data on bird intestinal length were collated as
 original data (BirdIntestine_Data.xlsx, first sheet) from the literature
 (BirdIntestine_Data_References.docx). Subsequently, weighted averages were
 calculated per species for each intestinal section separately, and
 supplemented with species-specific biological information
 (BirdIntestine_Data.xlsx, second sheet). The key spreadsheet contains the
 description of all the variables included. Empty cells represent missing
 data. Data was collected from two sources: scientific publications or
 through necropsies performed by the co-authors. Data were manually
 extracted from the publications. Data from published sources were only
 used if the publication included the species, body mass (kg), and length
 (cm) of the intestinal tract. If the literature included data for
 juveniles and adults, juvenile data were excluded. Additional unpublished
 data were obtained from a large set of post-mortem examinations carried
 out by the co-authors. ## Code/software The data is available in files
 compatible with the Microsoft suite. All analyses were made using R
 Studio.