Description of the Data and file structure

Two Excel spreadsheets and three structure files, contains 1) metadata for each sample used in the study; 2) environmental data for marsh patches used in dbRDA - one tab each for saltmarsh, Nelson's and seaside sparrow; and 3) genotype data for all individuals across the 3 species (final filtered SNP datasets used in the analyses in structure file format).

Details for sample metadata ('SupportingDatafile1')
Description: an Excel sheet with sample ID, species, location sampled, groupings and filenames used for the analysis, collector name, and if the sampled has been published previously.

Format:
Individual birds are in rows, each with a unique ID. Associated metadata belonging to that sample are in columns.

Dimensions: 725 rows x 13 columns

Variables:

• USGS AL band number for the bird in column A
• Species_Dataset: species of bird sampled (NESP, SALS, or SESP)
• Year_Sampled: the year which the sample was collected
• State: state in which the sample was collected
• Site: marsh site name from where the sample was collected
• Group: the population grouping that the sample belongs to that was used in analyses
• Negrouping: grouping which sampled belongs to and was used to calculated effective population sizes
• X_Coord: X coordinate of the sampling location
• Y_Coord: Y coordinate of the sampling location
• File_Name: the name of the file used in the analysis (this can be matched up to samples in STR files; name is made up of species, last 5 digits of band number, and sampling location)
• Collector: the collector of the sample
• In_Analyses: if the sample passed the filtering and was in the final dataset analyzed (Y/N)
• Publication: study listed for which samples were previously published. If no other publication exists, listed as "this study"

Details for marsh environmental data ('SupportingDatafile2')
Description: excel spread sheet of marsh-level environmental data used in the dbRDA to test the effects or landscape/environment on genetic differentiation taken from previously published GIS layer (Wiest et al., 2019). This data is filtered to exclude sites which did not have environmental data or which did not meet the sampling threshold for analysis (more than 3 individuals per marsh).

Format:
Unique mash IDs are in rows and associated environmental data are in columns. The excel sheet contains 3 tabs for each species - saltmarsh, Nelson's, and seaside sparrow.

Dimensions for tab 1 ('SALS_envData'): 33 rows x 12 columns
Dimensions for tab 2 ('NESP_envData'): 19 rows x 12 columns
Dimensions for tab 3 ('SESP_envData'): 15 rows x 12 columns

Variables (same in each tab):

• Loc: ID of the marsh in column A
• X_Coord: X coordinate of the sampling location
• Y_Coord: Y coordinate of the sampling location
• Patch_ID: the ID number from the GIS layer from which data was taken (Weist et al., 2019)
• samplesize: the amount of birds sampled from the marsh location
• State: state marsh is located in
• Marsh_area_ha: the area of the marsh patch sampled (in hectares; ha)
• high_marsh_prop: the proportion of high marsh vegetation of the marsh area (0-1). An area considered high marsh is dominated by Spartina patens, Spartina alterniflora short form, Juncus gerardii, and/or Distichlis spicata
• Marsh_150m: proportion of area that is marsh in a 150meter buffer around the patch
• Marsh_1000m: proportion of area that is marsh in a 1000meter buffer around the patch -sea-level_rise_trend: trends (changes) in mean sea level (rise or fall) in mm/year
• distance_to_coast: the distance of the sampling location to the Atlantic coastline, calculated from the patch layer using the measuring tool in QGIS

Details for filtered SNP datasets for each species ('SALS_final_SamplingLoc.str', 'NESP_final_SamplingLoc.str', & 'SESP_final_SamplingLoc.str')
Description: structure file for each species containing genotypes all of individual birds from fully filtered SNP dataset used in the final analysis.

Format:
First row contains a list of all the markers (loci)
Subsequent rows represent individual birds, with the genotype split across 2 consecutive rows for an individual. The first column is the bird ID, followed by the sampling location, and then locus information. Missing data are coded as '0' in these datasets.

Dimensions for saltmarsh sparrow ('SALS_final_SamplingLoc.str'): 567 rows x 5008 columns
Dimensions for Nelson's sparrow ('NESP_final_SamplingLoc.str'): 343 rows x 5854 columns
Dimensions for seaside sparrow ('SESP_final_SamplingLoc.str'): 283 rows x 2846 columns

Variables (same for each file):

• column A is unique bird ID / filename (including species, last 5 digits of the band number, and sampling site name)
• column 2 is the population or sampling location bird was sampled from (numerical: 1 through the total number of populations sampled)
• column 3-end of file: remaining columns are all the loci, including genotype at the locus for each individual