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 dete..., 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..., , # **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...