Migratory connectivity of North American waterfowl across administrative flyways

Abstract

Management of waterfowl that migrate seasonally across North America occurs within four flyways that were delineated in the early 1900s to include the annual movements of populations. Movements may have changed over the past century since the administrative flyways were established, and may do so while management plans are in use, so information about transitions among flyways through time can illustrate how management assumptions may change. Today there are more than 12 million records from 60 years of migratory waterfowl band recoveries to assess adaptive management approaches that will be most effective when they account for movements within and between flyways. We examined how much the movement of North American waterfowl occurs between flyways, whether those movements have changed through time, and whether movements of mallards are representative of multiple species, as suggested by current harvest management strategies. We estimated the probability a duck would transition from one flyway to another and the strength of migratory connectivity (MC) for each species within and among flyways. We used capture-mark-recovery models to estimate population-specific movement within and among flyways (transition probabilities) for 15 migratory waterfowl species that were banded during breeding and recovered during winter. We developed new functionality in the R package MigConnectivity to estimate the species-specific strength of MC using transition probability samples from the capture-mark-recovery models.We found the regular movement of duck populations among flyways, overall weak MC, and no consistent change in migratory movements through time. Mallard movements were median among all duck species, but significantly different from many species, particularly diving ducks. Despite the significant movement between flyways, our work suggests flyway management of waterfowl matches many of the seasonal movements of these species when considering mid-continent flyway management. We recommend models accounting for all transition probabilities between populations and regularly estimating harvest derivations, transition probabilities, and MC metrics to verify that the current movements match model assumptions.

Sixty-years of community-science data suggest earlier fall migration and short-stopping of waterfowl in North America

“…Mallard and Northern Pintail recoveries were found at two distinct wintering areas, one along the Pacific coast in northern California and the other in south-central United States. Mallard and especially Northern Pintail exhibit mixing between flyways, whereby individuals banded in one flyway are commonly recovered in another flyway (Buhnerkempe et al 2016, Roberts et al 2022). This mixing is thought to be due to movement and connection on the breeding grounds (Buhnerkempe et al 2016, Roberts et al 2022).…”

“…Mallard and especially Northern Pintail exhibit mixing between flyways, whereby individuals banded in one flyway are commonly recovered in another flyway (Buhnerkempe et al 2016, Roberts et al 2022). This mixing is thought to be due to movement and connection on the breeding grounds (Buhnerkempe et al 2016, Roberts et al 2022). We found a similar mixing of recoveries across flyways in our analysis; in particular, Northern Pintail banded in the central prairie province of Saskatchewan had recoveries spread across all 3 flyways.…”

“…Mallards are often used as a reference species for dabbling ducks in harvest management and habitat conservation plans, in part because of the large amount of data available for this species, but also because the single-species approach also allows for simplicity and cost benefits (Herbert et al 2021, Roberts et al 2022). However, patterns in fall migration are not consistent across species, as exemplified by the Blue-winged Teal here.…”

“…Early data exploration indicated Mallards banded in Alberta were substantially more likely to be recovered following the Pacific Flyway than Mallards banded in Saskatchewan or Manitoba, where migration typically followed the Mississippi and Central Flyways (collectively known as the Midcontinent). Mallards have been identified as having low to moderate migration connectivity (Roberts et al 2022), with most of the mixing between flyways occurring in the Mississippi Flyway (Buhnerkempe et al 2016). Because the relative proportion of birds banded in Alberta had changed over time, we chose to repeat the entire analysis to evaluate spatiotemporal changes in recovery distribution separately for (1) Mallards banded in Alberta and (2) Mallards banded in Saskatchewan or Manitoba.…”

“…This is important from a conservation perspective, as asynchrony between resource requirements and availability can negatively impact survival and reproduction (Newton 2007, Kirby et al 2008, Stafford et al 2014) and have been linked to declines in numerous migratory bird species (Baker et al 2004, van Bemmelen et al 2021). Moreover, shifting fall migration could decouple monitoring and management efforts from true population numbers (Devers et al 2021, Roberts et al 2022) and could substantially alter foraging pressures in wetland and agricultural habitats (Schummer et al 2014). Understanding changes to the timing and distribution of fall migration could also help direct waterfowl harvest policies by ensuring that hunting seasons coincide with waterfowl occurrence (Andersson et al 2022).…”