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

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.