DOI: 10.5061/dryad.4f4qrfjcs
title: Wing and bill measurements of Tyrannus round specimens identified to subspecies

description: Morphology is closely linked to locomotion and diet in animals. In animals
 that undertake long-distance migrations, limb-morphology is under
 selection to maximize mobility and minimize energy expenditure. Migratory
 behaviors also interact with diet, such that migratory animals tend to be
 dietary generalists, while sedentary taxa tend to be dietary specialists.
 Despite a hypothesized link between migration status and morphology,
 phylogenetic comparative studies have yielded conflicting findings. We
 tested for evolutionary associations between migratory status and limb and
 bill morphology across kingbirds, a pan-American genus of birds with
 migratory, partially migratory, and sedentary taxa. Migratory kingbirds
 had longer wings, in agreement with expectations if selection favors
 improved aerodynamics for long-distance migration. We also found an
 association between migratory status and bill shape, such that more
 migratory taxa had wider, deeper, and shorter bills compared to sedentary
 taxa. However, there was no difference in intraspecific morphological
 variation among migrants, partial migrants, and residents, suggesting that
 dietary specialization has evolved independently of migration strategy.
 The evolutionary links between migration, diet, and morphology in
 kingbirds uncovered here further strengthen ecomorphological associations
 that underlie long-distance seasonal movements in animals.
description: We measured bill length, width, and depth at the distal end of
 the nares. We also measured unflattened wing chord length, Kipp’s distance
 (a measure of wing pointedness: the distance between the tip of the first
 secondary feather to the tip of the longest primary feather; Kipp, 1942,
 1958; Baldwin <i>et al.</i>, 2010), tail length, and tarsus
 length on 2108 study skins from across the ranges of each species and
 subspecies (28 operational taxonomic units (OTUs)). MM measured 2008
 specimens, and identified all individuals to the lowest level of taxonomic
 identification (using Clements <i>et al.</i>, 2019) and
 classified each individual as migratory, partially migratory, or sedentary
 (<i>sensu</i> Fitzpatrick <i>et al.</i>,
 2004). JIGA measured 100 specimens to improve sampling of some taxa. Bill
 and tail measurements were taken twice and were confirmed to be within one
 mm of one another. Both right and left wing chords and tarsus lengths were
 measured and averaged. Measurements by JIGA were only taken once. We
 measured tail length as the longest rectrix to the nearest 0.1 cm (Pyle
 <i>et al.</i>, 1997). For most measurements, we used a
 Mitutoyo brand IP 67 digital calipers (part number 573-271) with a range
 of up to 15.24 cm, with 0.00127 cm resolution. For tails longer than 15.24
 cm, we used a 30.48 cm stainless steel ruler placed between the two middle
 rectrices. When tails were longer than 30.48 cm photos were taken of the
 tails above a 0.64 x 0.64 cm square grid with the calipers measuring to
 their extent and ImageJ was used to calculate the full tail length
 (Supporting Information 2). We then averaged measurements across
 individuals within each OTU for downstream analyses.
description: The readme file contains an explanation of each of the variables
 in the dataset, and its measurements units. Information on how the
 measurements were done can be found in the associated manuscript
 referenced above. Below we detail special cases to be aware of in this
 dataset. Some specimen tags did not reflect complete
 data, and when data was incomplete we made a couple of adjustments that
 are reflected in the attached data set. These did not affect our analyses,
 but should be noted for future use of the dataset. For specimens that were
 dated to 18--, meaning some time in the 1800s, we changed the cell to read
 'null'. This occured for the following specimen numbers that all
 originated from the Smithsonian collection: 120074, 52806, 7389, 38191,
 39457, 49586, 71196, 101425, 129146. Some specimens had collection years
 listed without the century noted (e.g., '40 instead of clarifying
 whether the specimen was from 1840 or 1940). We assumed these were from
 the 1900s because that was most likely and changed the year to 1940 in the
 year column. This occurred for the following specimen numbers that all
 originated from the Smithsonian collection: 356917, 356918, 359886,
 531616, 531617. For specimen 30633 from the Louisiana State University
 Museum of Natural Science collection, the exact date was not specified and
 instead a potential range from 20-25th of the month. For this specimen we
 selected the first possible day (i.e., the 20th in this case) for the day
 column. Lastly, two specimens from the Royal Ontario Museum did not have
 catalogue numbers, but instead had an older version of a collection number
 (i.e., "30,6,21,450" and "33,9,1,676"). We changed
 these to numbers without commas to match how the specimen ID was labelled
 for the rest of the dataset. For any cells where no data was given on
 specimen tags for that specimen in any column, the cells read
 'null'. Accurate morphological measurements
 were not possible for all metrics used in this study, and where these were
 not possible the cell reads 'null'.