Measuring avian bill size: Comparing and evaluating 3D surface scanning with traditional size estimates in Australian birds

Unidimensional measurements for estimating bill size, like length and width, are commonly used in ecology and evolution, but can be criticised due to issues with repeatability and accuracy. Furthermore, formula-based estimates of bill surface area tend to assume uniform bill shapes across species, which is rarely the case. 3D surface scanning can potentially help overcome some such issues by collecting detailed external morphology and direct measurements of surface area, rather than composite estimates of size. Here, we evaluate the use of 3D surface scanners on avian museum specimens to test the repeatability of 3D-based measurements and compare these to traditional formula-based methods of estimating bill size from unidimensional measurements. Using 28 Australian bird species, we investigate inter-observer repeatability of surface area measurements from 3D surface scans. We then compare 3D-based size estimates to formula-based size estimates to infer the accuracy and precision of form..., , , # Measuring avian bill size: comparing and evaluating 3D surface scanning with traditional size estimates

[https://doi.org/10.5061/dryad.sxksn038q](https://doi.org/10.5061/dryad.sxksn038q)

We investigated measurement repeatability between observers for bill surface area, as derived from 3D scans. We applied 3D surface scans on a diverse set of birds, and further collected unidimensional measurements. We assess how these unidimensional measurements can be used in different formulae to estimate bill surface area.

## Description of the data and file structure

The dataset contains bill surface area measurements, extracted from two observers using 3D surface scans of diverse bird species (columns billSA_measurer1 and 2). It also contains unidimensional measurements (bill length, width, depth, width between the nares, and upper and lower bill profile length; as titled in columns), measured using calipers (or, in the case of total bill width and the profile length, derived from the 3D scan...,