DOI: 10.5061/dryad.2ngf1vhwh
title: Data from: Natural selection after severe winter favors larger and duller bluebirds

description: Extreme cold events, which have become more frequent, can revert the
 direction of long-term responses to climate change. In 2021, record
 snowstorms swept the United States, causing wildlife die-offs that may
 have been associated with rapid natural selection. Our objective was to
 determine if the snowstorms caused natural selection in Eastern Bluebirds
 (Sialia sialis). To test which mechanism most influenced their survival,
 we measured the morphology and coloration of fatalities and survivors at
 three sites. Survival was associated with a longer tarsus, and a wider,
 longer, and deeper beak in support of the starvation and thermal endurance
 hypotheses. Additionally, bluebirds with more-ornamented plumage were less
 likely to have survived, maybe because of an early energy investment in
 mate and site acquisition. As bluebirds encounter increasingly warm summer
 conditions, the longer extremities favored during the snowstorms may
 continue to be favored through their thermoregulatory benefits. However,
 the dull plumage coloration favored by natural selection during the
 snowstorms may be opposed by sexual selection benefits of more-ornamented
 plumage. Overall, responses to extreme events are difficult to predict
 from responses to long-term climate change, and responses to one event
 such as the 2021 snowstorms may not predict responses to a future extreme
 event.
description: # Data from: Natural selection after severe winter favors larger and
 duller bluebirds Rolland V.*, Grindstaff J., Balenger S., and Siefferman
 L. *Corresponding author:
 [vrolland@astate.edu](mailto:vrolland@astate.edu) 
 [https://doi.org/10.5061/dryad.2ngf1vhwh](https://doi.org/10.5061/dryad.2ngf1vhwh) ## Descripiton of the data files This document describes columns in Excel files used for the study of natural selection in Eastern Bluebirds that survived the 2021 snowstorms in the south-central US. Only fatalities encountered in nest boxes were included in the first file, but both fatalities and survivors caught during the nesting season that followed the storms are included in the second file. Scripts are for analyses in Program R. Scripts for analyses were run in Program R version 4.4.1 on Windows 11 x64. **Responsibilities** ·         Data collection: Rolland (AR), Grindstaff (OK), Balenger (MS) collected feathers from and measured dead and live bluebirds ·         Feather data: Siefferman (NC) prepared and analyzed feathers for coloration variables ·         R Code: Rolland compiled the data and wrote the code ## Data structure ### Repeatability\_MasterData\_for\_AmNat.csv This file includes measurements on various bluebird morphological traits. When a bird was missing a tail feather, we entered an NA value, which was also necessary for the asymmetry variable. Similarly, if a bird was in poor condition (e.g., bent wing, degraded bill), we used NA as a value for the impacted variable. We used the file to determine whether our measurements were accurate through an analysis of repeatability of three sets of measurements on the same traits. Columns are as defined as follows: ·         **State**: two-letter code for US state ·         **Bird**: Unique bird ID number. If a bird was already banded, its ID was the band number. If not previously banded, the number was made up with a site-specific system. ·         **Sex**: Two-category variable with F for female and M for male ·         **Round**: Each bird was measured three times in a random order each time. Round refers to the first, second, or third round of measurements. ·         **Wleft** and **Wright**: Relaxed wing chord for left and right wings measured in mm. ·         **Wasym**: Absolute difference in wing chord (mm) between left and right wings. ·         **Bwidth**, **Blength**, and **Bdepth**: Beak width, length, and depth measured in mm. ·         **Lleft** and **Lright**: Tarsus length for left and right tarsus in mm. ·         **Lasym**:  Absolute difference in tarsus length (mm) between left and right legs (tarsi). ·         **Tleft** and **Tright**: Left and right outermost tail feather (rectrix R6) length in mm. ·         **Tmiddle**: Middle tail feather length (rectrix R1) in mm ·         **Tasym**: Absolute difference in length (mm) of outermost tail feathers (rectrices R6) between left and right. ### Natural Selection\_MasterData\_for\_AmNat.csv This file includes raw and derived measurement for various bluebird morphological and plumage coloration traits. When a bird was missing a tail feather, we entered an NA value, which was also necessary for the asymmetry variable. Similarly, if a bird was in poor condition (e.g., bent wing, degraded bill, bare belly), we used NA as a value for the impacted variable. We used the file to determine if natural selection occurred and on which traits through various approaches (model selection, principal component analysis, and selection gradients/differentials). Columns are as defined as follows: #### Demographic data ·         **State**: two-letter code for US state ·         **Box**: Nest box ID in which a fatality was collected or at which a survivor was captured during a nesting attempt. ·         **Sex**: Two-category variable with F for female and M for male ·         **BirdID**: Unique bird ID number. If a bird was already banded, its ID was the band number. If not previously banded, the number was made up with a site-specific system. ·         **Survived**: Binary variable to indicate whether a bird was measured as a fatality (N) or as a live bird (Y). ·         **Recap**?: Binary variable to indicate whether a bird had been previously banded and therefore  measured as a recaptured bird (Y) or as a new individual (N). #### Morphological traits ·         **WCleft** and **WCright**: Relaxed wing chord for left and right wings measured in mm. ·         **BW**, **BL**, and **BD**: Beak width, length, and depth measured in mm. ·         **TRleft** and **TRright**: Tarsus length for left and right tarsus in mm. ·         **TLleft** and **TLright**: Left and right outermost tail feather (rectrix R6) length in mm. ·         **TLmiddle**: Middle tail feather length (rectrix R1) in mm ·         **BV ** and **BS**: Beak volume (mm3) and beak surface area (mm2) calculated from values of beak depth, width, and length, using volume and surface area formulas for an elliptic cone. #### Plumage coloration traits ·         **BellyB**: Belly brightness (total amount of light reflected by the feather) measured as the summed reflectance (over 5 readings of 20 reflectance curve per reading) in nm from 6–8 feathers of the white belly region from each bird. ·         **BreastB**: Breast brightness (total amount of light reflected by the feather) measured as the summed reflectance (over 5 readings of 20 reflectance curve per reading) in nm from 6–8 feathers of the chestnut breast region from each bird. ·         **BreastRC**: Breast red chroma measured as the ratio of the total reflectance in the red range to the total reflectance of the entire spectrum (∫645-700/∫300-700) using 6–8 feathers from the chestnut breast region of each bird. ·         **RumpB**: Rump brightness (total amount of light reflected by the feather) measured as the summed reflectance (over 5 readings of 20 reflectance curve per reading) in nm from 6–8 feathers of the blue rump region from each bird. ·         **RumpUVC**: Rump UV chroma (spectral purity) measured as the ratio of the total reflectance in the ultraviolet range to the total reflectance of the entire spectrum (∫300-400/∫300-700) using 6–8 feathers from the blue rump region of each bird. ·         **RumpH**: Rump hue measured as the wavelength (nm) at peak reflectance, from 6–8 feathers from the blue rump region of each bird. ·         **TailB**: Belly brightness (total amount of light reflected by the feather) measured as the summed reflectance (over 5 readings of 20 reflectance curve per reading) in nm from the right outer tail feather (rectrix R6) from each bird. ·         **TailUVC**: Tail UV chroma (spectral purity) measured as the ratio of the total reflectance in the ultraviolet range to the total reflectance of the entire spectrum (∫300-400/∫300-700) using the right outer rectrix of each bird. ·         **TailH**: Tail hue measured as the wavelength (nm) at peak reflectance, from the outer rectrix of each bird. ## Code ### Repeatability analyses\_script\_for\_AmNat.r This file contains the code used to run the repeatability analyses based on data in Repeatability_MasterData_for_AmNat.csv described above. The only package used is rptR version 0.9.22. ### Natural selection analyses\_script\_for\_AmNat.r This file uses the file labeled Natural selection_MasterDara_for_AmNat.csv described above. The code assumes that this script is saved in the same folder as the csv file. If not, the user will need to properly set the working directory. After a list of packages and some code to import and prepare the data, this file of codes is organized by analysis in the same order as analyses appear in the manuscript. Headings are collapsible for a sort of Table of Content, which can also be found in the drop-down menu in the bottom edge of the script window in RStudio for an easier navigation among sections. The code for the figures presented in the manuscript is embedded in this script under their respective analyses as well as references to Tables and manuscript sections/paragraphs. Packages used in this script are as listed alphabetically with their version below: ·         ade4                version 1.7-22 ·         AICcmodavg  version 2.3-3 ·         corrplot            version 0.92 ·         effects             version 4.2-2 ·         emmeans         version 1.10.3 ·         factoextra        version 1.0.7 ·         FactoMineR    version 2.11 ·         ggeffects         version 1.7.0 ·         ggplot2            version 3.5.1 ·         ggpubr             version 0.6.0 ·         lme4                version 1.1-35.5