10.1371/journal.pone.0115143.g003 Pär Söderquist Pär Söderquist Joanna Norrström Joanna Norrström Johan Elmberg Johan Elmberg Matthieu Guillemain Matthieu Guillemain Gunnar Gunnarsson Gunnar Gunnarsson Measurement of bill length. Public Library of Science 2014 bill morphology Farmed mallards fitness consequences hunting purposes study system anthropogenic impact Wild populations Wild Mallards mallard population anthropogenic influence bill lamellae 2014-12-16 02:48:25 Figure https://plos.figshare.com/articles/figure/_Measurement_of_bill_length_/1272395 <p>Bill length was measured (to nearest 0.01 millimeter) along the dorsal side of the maxilla using a caliper. Photograph: Pär Söderquist.</p>