Data from: Shared temporal increases in bill size among songbirds of the San Francisco bay area are due to different seasonal selective pressures
Data files
Apr 22, 2025 version files 211.66 KB
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Appendix_S1_morph_clim_data.xlsx
207.88 KB
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README.md
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Abstract
Museum specimens offer a unique and powerful tool for understanding the impact of anthropogenic change on populations over time. Morphological traits can be impacted by many different environmental variables that are difficult to separate from one another as potential driving factors. Comparative analyses among similar species jointly experiencing change in the same environmental variables can help pinpoint the selective pressures driving temporal morphological change. We assessed temporal change in bill size, tarsus length, and body size between six species of songbirds from the San Francisco Bay Area over the past 150 years. Wing length, as a proxy for body size, exhibited idiosyncratic temporal changes among species. In contrast, we found a significant increase in bill surface area across all but one species. Quantile regression analyses on bill size variation additionally revealed that temporal increases over the past century have been driven by increases in the largest bill sizes in some species, but increases in the smallest bills over time in others. The climate variables best explaining temporal change in bill size also differed among species with some species responding more to changing summer variables (e.g. maximum annual temperature) and others in response to a changing winter climate. These results together suggest that different sympatric, resident bird species may be experiencing temporal morphological change in response to selective pressures experienced at different seasons. Our finding provides support for the season of critical thermal stress hypothesis that suggests variation in functional traits will be shaped by the season that imposes the greatest selective force on a population. Overall, this study has important implications for future research on the role of bills in thermoregulation and for conservation efforts based on the adaptive capacity of birds to respond to climate change.
https://doi.org/10.5061/dryad.98sf7m0v5
Description of the data and file structure
Dataset of morphological measurements from 1,001 bird specimens of six species. Morphological characters include: bill length, bill width, bill depth, wing length and tarsus length. Dataset also includes specimen voucher numbers, locality coordinates, and time of collection. Finally, the data includes climate data extracted from PRISM dataset for year and location of specimen collected. Climate variables include: annual maximum temperature, annual minimum temperature, annual maximum vapor pressure deficit, annual minimum vapor pressure deficit. We also calculated 3 and 5-year averages of each climate parameter before year of collection for each specimen. Cells in the dataset with NA represent cases where data is missing. This is due either to damaged morphological character on the specimen or lack of data for a specific year in the climate data.
Files and variables
File: Appendix_S1_morph_clim_data.xlsx
Description: Specimen, morphological, and climate data.
Variables
- Catalog: museum catalog number for specimen
- InstitutionNumber: GUID identifier for each specimen including institution:collection:catalog number
- Species: alpha code for each species (SAVS: Savannah Sparrow; SOSP: Song Sparrow; HOFI: House Finch; CALT: California Towhee; RWBL: Red-winged Blackbird; DEJU: Dark-eyed Junco)
- Sex: sex of specimen
- Age: developmental stage of specimen
- Year: year of collection for specimen
- Month: month of collection from 1=January to 12=December
- County: county collected in Californai
- Latitude: latitudinal coordinates
- Longitude: longitudinal coordinates
- BillLength: length of bill measured from nares in mm
- BillWidth: with of bill measured at nares in mm
- BillDepth: depth of bill measured at nares in mm
- WingLength: unflattened wing chord measurement of bird in mm
- TarsusLength: length of the tarsus measured in mm
- Sample_Ann_Tmax, Sample_5yr_Ann_Tmax, Sample_3yr_Ann_Tmax: Annual maximum temperature (celsius) from PRISM database. Included are annual Tmax for year of collection, average of 5 years before collection, and average of 3 years before collection
- Sample_Ann_Tmin, Sample_5yr_Ann_Tmin, Sample_3yr_Ann_Tmin: Annual minimum temperature (celsius) from PRISM database. Included are annual Tmin for year of collection, average of 5 years before collection, and average of 3 years before collection
- Sample_Ann_Vpdmax, Sample_5yr_Ann_Vpdmax, Sample_3yr_Ann_Vpdmax: Annual maximum vapor pressure deficit (hectopascal hPA) from PRISM database. Included are annual VPDmax for year of collection, average of 5 years before collection, and average of 3 years before collection.
- Sample_Ann_Vpdmin, Sample_5yr_Ann_Vpdmin, Sample_3yr_Ann_Vpdmin: Annual minimum vapor pressure deficit (hectopascal hPA) from PRISM database. Included are annual VPDmin for year of collection, average of 5 years before collection, and average of 3 years before collection.
- Sample_Ann_Prec, Sample_5yr_Ann_Prec, Sample_3yr_Ann_Prec: annual precipitation totals (mm) from PRISM database. Included are annual precipitation for year of collection, average of 5 years before collection, and average of 3 years before collection.
Code/software
Spreadsheet that can be viewed or analyzed in various programs (e.g. excel, numbers, R).
Access information
Data was derived from the following sources:
- Museum specimens
- PRISM climate group: https://prism.oregonstate.edu/normals/
The dataset includes morphological measurements made from 1,001 museum specimens at Museum of Vertebrate Zoology, University of California Berkeley and California Academy of Sciences. Measurements were all made using digital calipers. Climate variables for each specimen come from the PRISM climate database and were extracted using locality info from each specimen.