DOI: 10.5061/dryad.z34tmpgnz
title: Morphometrics of mallards in the Lower Mississippi Alluvial Valley and associated climate variables from 1979-2021

description: Body mass in overwintering waterfowl is an important fitness attribute as
 it affects winter survival, timing of spring migration, and subsequent
 reproductive success. Recent research in Europe and the western United
 States indicates body mass of mallards (Anas platyrhynchos) has increased
 from the late 1960s to early 2000s. The underlying mechanism is currently
 unknown; however, researchers hypothesize that increases are due to a more
 benign winter climate, increased food availability through natural and
 artificial flooding, introgression of wild mallard populations by
 game-farm mallards, or shifting of wintering distributions northward.
 Further investigation of factors related to winter mallard body mass
 increases and whether this phenomenon is occurring in other major flyways
 could increase understanding of intrinsic and extrinsic variables
 influencing waterfowl fitness. We collected and analyzed mallard body mass
 data in the Lower Mississippi Alluvial Valley from 1979 to 2021 to
 determine sources of temporal variation. We measured hunter-harvested
 mallards from private hunting clubs, public hunting areas, and
 duck-plucking businesses. Mallard body mass increased by approximately 6%
 among all age-sex classes from 1979 to 2021. We also compiled weather data
 (rainfall [cm], weather severity index information [WSI], river gage
 discharge [cfs] and height [m]) to relate to mallard body mass
 measurements.
description: To analyze age and sex differences among and within years from
 1979 to 2021, we categorized each mallard into one of four classes
 comprised of adult males, adult females, juvenile males, and juvenile
 females, referred to as AgeSex. To explore how mallard body mass has
 changed from 1979 to 2021, we used year as a fixed effect within our
 models. Because study years (or duck hunting seasons) span calendar years
 (often Nov-Feb), for clarity our use of the term “year” refers to the duck
 hunting season initiating in November of that year and spanning to
 February of the next calendar year. Days refer to chronological days
 within hunting seasons. Because hunting season dates varied among years,
 we represented days within seasons as modified Julian days, with the
 earliest date that a mallard’s mass was measured across the study labeled
 as day 1 (November 19th) and each subsequent day numbered sequentially
 until day 83 (Feb 13th), the latest date a bird was measured.
 To assess the relationship of cumulative rainfall and cold
 weather severity (or Weather Severity Index developed by Schummer et al.,
 2010; WSI) with mallard body mass, we compiled climate data from
 representative National Oceanic and Atmospheric Administration (NOAA)
 weather stations. The variables we used were daily cumulative
 precipitation (cm) and minimum and maximum daily temperature (°C). We
 obtained data from Yazoo City, Yazoo County, Mississippi (station name:
 Yazoo City 5 NNE) for winters 1979–1980 through 1982–1983 and from
 Arkansas (station names: Stuttgart 9 ESE, Des Arc, Searcy, Georgetown,
 Pine Bluff, Augusta, Wynne, Alicia, Keiser, Eudora, Monticello Municipal
 Airport, Marianna, Arkansas Post, Rohwer, Paragould, and Pocahontas) for
 winters 1990–1991, 1999–2000 through 2003–2004, 2015–2016, 2016–2017,
 2019–2020, and 2020–2021 based on proximity of sampling sites and weather
 stations. We recognize that daily rainfall on a given date may not be the
 best measure of how precipitation influenced body mass on the date of
 harvest. Because the known movement of waterfowl before measurement of
 body mass was unknown, and it can take waterfowl anywhere from 8 to
 72 h to digest most food resources (Charalambidou et al., 2005), we
 calculated a 3-day cumulative rainfall before the dates of mallard
 measurement to more accurately represent the relationship between
 precipitation and mallard body mass. Similarly, we did not use in our
 analysis the daily average temperature from the day that a bird was
 measured. Instead, we calculated daily average temperatures for each day
 and season and used these values to calculate a 3-day mean of daily
 average temperatures before mallards were measured. Finally, we calculated
 WSI using our 3-day mean temperatures (by modifying the WSI equation from
 Schummer et al., 2010) to evaluate the relationship of weather severity
 and mallard body mass. We modified the WSI equation to use three-day means
 rather than two-week means because we wanted to represent cumulative of
 temperature experienced by ducks more recently before measurement (See Eq.
 (1) in Veon et al. 2023). Finally, we used river gage
 height (m) data as a function of flooding. River gage height values were
 identified using associated discharge (cfs) values from rate tables
 obtained from the USGS Lower Mississippi-Gulf Water Science Center for
 Mississippi winters 1979–1983 (gage name: Big Black River near Bovina) and
 for Arkansas winters 1990–1991,1999–2000 through 2003–2004, 2015–2016,
 2016–2017, and 2019–2020, and 2020–2021 (gage names: Black River near
 Corning, Black River at Pocahontas, Black River at Black Rock, Cache River
 at Egypt, White River at Newport, White River at Georgetown, Cache River
 near Cotton Plant White River at DeValls Bluff, L′Anguille River near
 Colt, L′Anguille River near Palestine, Bayou Meto near Lonoke, Bayou
 Bartholomew at Garrett Bridge, and Bayou Bartholomew near McGehee). We
 collected data from river gages nearest our sample sites to examine the
 relationship of daily river height to mallard body mass. Similar to
 rainfall, we expected mallard body mass would be greater when river levels
 were higher because of increased foraging habitat. Importantly, we found
 rainfall and river gage height were not highly correlated (Pearson
 Correlation [r] = 0.25). This result may indicate that rivers can
 fluctuate from rainfall upstream of areas absent of local rainfall or by
 human control (e.g., locks, dams, levees) (Junk et al., 1989; MRC, 2007).
 Additionally, forage availability may reflect different combinations of
 rainfall and river flooding. Rainfall may be more influential in flooding
 habitat not connected to or near river systems (e.g., puddling or
 ponding), whereas river flooding more likely to provides access to
 foraging habitat in riparian and adjacent overbank habitats (Smith and
 Callahan, 1983; Galat et al., 1998, Heitmeyer, 2006).
description: # **Morphometrics of mallards in the Lower Mississippi Alluvial Valley and
 associated climate variables from 1979-2021**
 [https://doi.org/10.5061/dryad.z34tmpgnz](https://doi.org/10.5061/dryad.z34tmpgnz) **Date of data collection (range; yyyy-mm-dd to yyyy-mm-dd):** 1979-12-08 to 2021-02-06 **Geographic location of data collection:** Numerous locations across Arkansas and Mississippi, USA. Exact locations are not provided for privacy of private landowners and public land hunter locations. Instead, unique location identifiers are provided by using numbers, but general area locations can be found in the river gage, rain gage, and weather severity index (WSI) station information. Nearby cities include, but are not limited to Yazoo City [MS], Stuttgart [AR], Des Arc [AR], Georgetown [AR], Pine Bluff [AR], Lynne [AR], etc. All data resides in the Lower Mississippi Alluvial Valley. **Information about funding sources that supported the collection of the data:** Ducks Unlimited Southern Regional Office; Arkansas Game and Fish Commission; The Harry and Jo Leggett Family; Arkansas Audubon Society Trust; U.S. Fish and Wildlife Service; J. Long at the US Geological Survey Oklahoma Cooperative Fish and Wildlife Research Unit; and the US Geological Survey Arkansas Cooperative Fish and Wildlife Research Unit. ## Description of the data and file structure We compiled body mass measurements from several different published studies (Delnicki and Reinecke, 1986, Dabbert et al., 1997, Dabbert and Martin, 2000) as well as from data the authors have collectively accumulated from 1979 to 2021. Thus, sample sites and methods varied somewhat across periods. We included body mass measurements of mallards collected during the Mississippi duck hunting seasons of 1979–1980 through 1982–1983, as well as Arkansas duck hunting seasons of 1990–1991, 1999–2000 through 2003–2004, 2015–2016, 2016–2017, 2019–2020, and 2020–2021. Although study sites varied among periods, most study sites were relatively in the same geographic proximity of the Lower Mississippi Alluvial Valley (LMAV). Therefore, for consistency, we did not include measurements from additional states in more recent years. We collected data from public and private lands, as well as from duck cleaning businesses. In sample years 1979–1980 through 1982–1983 and 1999–2000 through 2003–2004, esophageal contents were removed from waterfowl before measurements were made. In sample years 1990–1991, 2015–2016, 2016–2017, 2019–2020, and 2020–2021 waterfowl were weighed without the removal of esophageal contents. However, in sample years 2019–2020 and 2020–2021, the amount of food in the esophagus was estimated (none [0 g], small [0–20 g], or large [&gt;20 g]) through palpation. Waterfowl in the “large” amount category were removed from analyses. Additionally, in all study years, we excluded mallards with missing limbs, body parts, or birds that contained excessively wet feathers. Dataset consists of one excel sheet shows mallard body mass and wing length metrics and climate variables associated within and among sample years. **Data filename:**  Morphometrics_of_Mallards_in_the_Lower_Mississippi_Alluvial_Valley_and_Associated_Climate_Variables_from_1979_2021.xlsx **Dataset dimensions:** Number of variables: 22 Number of cases/rows: 6,308 rows **Variable list and description:**  MALLARD_ID (ID number for each unique mallard and associated measurements) LOC_NUM (ID number for each unique study location within the LMAV) YEAR (Calendar year of sample date) MONTH (Month of sample date) DAY (Day of sample date) DATE (Calendar day of sample date) DOS (Numerical day of season; Day 1 = Nov 19th) SEAS_NUM (Chronological number of duck hunting season from 1979-1980 [1] through 2020-2021 [42]) DECADE_NUM (Chronological number of respective decade; Decade 1 = 1979–1980 through 1988–1989, Decade 2 = 1989–1990 through 1998–1999, Decade 3 = 1999–2000 through 2008–2009, Decade 4 = 2009–2010 through 2018–2019, and Decade 5 = 2019–2020 through 2020–2021). SEX (Male or female mallard) AGE (A = After hatch year or &gt; 1 year old and H = Hatch Year or &lt; 1 year old) AGESEX (1 = adult male, 2 = adult female, 3 = juvenile male, 4 = juvenile female) BODY_MASS (Mallard mass in grams) WING_LENGTH (Wing length measured using wing-notch length from Carney et al. 1992) FOOD_ESOPH (1 = none [0 g], 2 = small [0–20 g], 3 = large [&gt;20 g]) RAIN_STATION (Nearby town and state in the US where rainfall [cm] was recorded) RAIN_CM (Average 3-day rainfall [cm] before harvest) WSI_STATION (Nearby town and state in the US where rainfall [cm], temperature [C], and snow depth [cm] was recorded) WSI (Weather Severity Index calculation using 3-day mean of temperatures [C] before harvest; See Eq[1] in Veon et al. 2023) RIVER_GAGE (Nearby town and state in the US where river discharge [cfs] and river height [m] was recorded) RIVGAGE_DISCHARGE (Daily discharge [cfs] recorded by nearest river gage to mallard harvest location) RIVGAGEHEIGHT_M (Daily river height [m] derived from USGS rate tables relating to daily discharge [cfs] measurements for each river gage closest to mallard harvest locations) Note: if "n/a" exists in any cell, that means this data was unavailable or unable to be measured for that specific sample point. ## Sharing/Access information **Data was derived from the following sources:** *Main publication that uses all data:*  Veon et al. (2023) [uses all data; this paper should be cited when using this dataset] : [https://www.sciencedirect.com/science/article/pii/S2351989423000033](https://www.sciencedirect.com/science/article/pii/S2351989423000033) *Additional publications that use portions of this dataset:* Veon et al. (2024) (2019-2021 body mass and wing length data only): [https://wildlife.onlinelibrary.wiley.com/doi/full/10.1002/jwmg.22509](https://wildlife.onlinelibrary.wiley.com/doi/full/10.1002/jwmg.22509) Veon (2021) (MSc Thesis): [https://scholarworks.uark.edu/etd/4330/](https://scholarworks.uark.edu/etd/4330/) Dabbert and Martin (2000) [1990’s data only]: [https://bioone.org/journals/journal-of-field-ornithology/volume-71/issue-3/0273-8570-71.3.423/DIET-OF-MALLARDS-WINTERING-IN-GREENTREE-RESERVOIRS-IN-SOUTHEASTERN-ARKANSAS/10.1648/0273-8570-71.3.423.short](https://bioone.org/journals/journal-of-field-ornithology/volume-71/issue-3/0273-8570-71.3.423/DIET-OF-MALLARDS-WINTERING-IN-GREENTREE-RESERVOIRS-IN-SOUTHEASTERN-ARKANSAS/10.1648/0273-8570-71.3.423.short) Dabbert et al. (1997) [1990’s data only]: [https://meridian.allenpress.com/jwd/article/33/1/57/121955/USE-OF-BODY-MEASUREMENTS-AND-SERUM-METABOLITES-TO](https://meridian.allenpress.com/jwd/article/33/1/57/121955/USE-OF-BODY-MEASUREMENTS-AND-SERUM-METABOLITES-TO) Delnicki and Reinecke (1986) [1979-1983 data only]: [https://www.jstor.org/stable/3801486?origin=crossref](https://www.jstor.org/stable/3801486?origin=crossref) ## Code/Software Data was processed using R Computing Software [R Core Team 2020])