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Morphometrics of mallards in the Lower Mississippi Alluvial Valley and associated climate variables from 1979-2021

Cite this dataset

Veon, John T. et al. (2024). Morphometrics of mallards in the Lower Mississippi Alluvial Valley and associated climate variables from 1979-2021 [Dataset]. Dryad.


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.

README: Morphometrics of mallards in the Lower Mississippi Alluvial Valley and associated climate variables from 1979-2021

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 [>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: 


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 > 1 year old and H = Hatch Year or < 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 [>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] :

Additional publications that use portions of this dataset:

Veon et al. (2024) (2019-2021 body mass and wing length data only):

Veon (2021) (MSc Thesis):

Dabbert and Martin (2000) [1990’s data only]:

Dabbert et al. (1997) [1990’s data only]:

Delnicki and Reinecke (1986) [1979-1983 data only]:


Data was processed using R Computing Software [R Core Team 2020])


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).


Ducks Unlimited, Award: 008127, Southern Regional Office

Arkansas Game and Fish Commission, Award: 1434–04HWRU1567, Cooperative agreement

The Harry and Jo Leggett Family

Arkansas Audubon Society Trust

U.S. Fish and Wildlife Service

United States Geological Survey, Oklahoma Cooperative Fish and Wildlife Research Unit

United States Geological Survey, Arkansas Cooperative Fish and Wildlife Research Unit