Examining inter-regional and intra-seasonal differences in wintering waterfowl landscape associations among Pacific and Atlantic flyways

The Central Valley of California (CVC) and Mid-Atlantic (MA) in the U.S.
are both critical sites for nationwide food security (California Poultry
Federation 2016, Prosser et al. 2017), and many waterfowl species
annually, especially during the winter, providing feeding and roosting
locations for a variety of species. Mapping waterfowl distributions, using
NEXRAD, may aid in the adaptive management of important waterfowl habitat
and allow various government agencies to better understand the interface
between wild and domestic birds and commercial agricultural practices. We
used 9 years (2014–2023) of data from the US NEXRAD network to model
winter waterfowl relative abundance in the CVC and MA as a function of
weather, temporal period, environmental conditions, and landcover
characteristics using Boosted Regression Tree modelling. We were able to
quantify the variability in effect size of 28 different covariates across
space and time within two geographic regions which are critical to
nationwide waterfowl management and host a high density of nationally
important commercial agriculture. In general, weather, geographic
(distance to features), and landcover condition (wetness index) predictors
had the strongest relative effect on predicting wintering waterfowl
relative abundance in both regions, while effects of land cover
composition were more regionally and temporally specific. Increased daily
mean temperature was a major predictor of increasing relative waterfowl
abundance in both regions throughout the winter. Increasing precipitation
had differing effects within regions, increasing relative waterfowl
abundance in the MA, while decreasing in general within the CVC.
Increasing relative waterfowl abundance in the CVC is strongly tied to the
flooding of the landscape and rice availability, whereas waterfowl in the
MA, where water is less limiting, are generally governed by waste grain
availability and emergent wetland on the landscape. Waterfowl relative
abundance in the MA was generally higher nearer to the Atlantic coast and
lakes, while in the CVC they were higher nearer to lakes. Our findings
promote a better understanding of spatial associations of waterfowl to
landscape features and may aid in conservation and biosecurity management
protocols.