Evidence for Black Duck Winter Distribution Change

Brook, Rodney W.; Ross, R. Kenyon; Abraham, Kenneth F.; Fronczak, David L.; Davies, J. Chris

doi:10.2193/2007-424

Cited by 24 publications

(37 citation statements)

References 12 publications

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“…Black duck numbers wintering in eastern Ontario were stable during 1986-1996, but increased sharply (20%/y) during 1997-2005, a time when breeding numbers in northern Ontario remained stable, suggesting breeding population increases were not leading to the increases seen in wintering areas in Ontario (Brook et al 2009). Instead, black duck numbers wintering in eastern Ontario increased during years Table 1.…”

Section: Discussionmentioning

confidence: 97%

“…Bayesian P values near 0.5 indicate good model fit, while values near 0 or 1 suggest poor fit. when numbers of black ducks counted in the Mississippi Flyway midwinter inventory were lower (Brook et al 2009), suggesting a distributional change and more birds wintering farther north. A similar phenomenon may be occurring in Nova Scotia, and Atlantic Canada generally, with more birds wintering farther north.…”

Section: Discussionmentioning

confidence: 99%

“…Declines in black ducks observed in traditional wintering sites may be explained in part by a decline in the quality or quantity of nonbreeding habitat (Conroy et al 2002), and perhaps by a redistribution of birds wintering farther north (Brook et al 2009). Christmas Bird Count (a volunteer-based bird survey conducted in late December) data indicated increases in the northeastern United States in winter (Link et al 2006).…”

Section: Introductionmentioning

confidence: 99%

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Increases in the Number of American Black Ducks Wintering in Nova Scotia, 1970–2015

Robertson

Tomlik

Milton³

et al. 2017

Journal of Fish and Wildlife Management

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Despite extensive conservation and management efforts, American black duck (Anas rubripes) populations remain below desired population levels. Researchers have noted declines at a number of wintering areas, but indications are that wintering populations in the northern part of the range are increasing. Intermittently between 1970 and 1989, and annually since 1992, wildlife biologists have flown aerial surveys of the entire coast of Nova Scotia, Canada, to count wintering waterfowl. This survey counted the total number of ducks seen in predefined lengths of coastline. We analyzed those survey data using generalized linear mixed models, over the entire time period and in the recent time period (1992-2015, when surveys were done every year), across five general regions of Nova Scotia. We fit models using Bayesian methods with uninformative priors; models with negative binomial response distributions performed well. Due to the large variation in mean numbers of black ducks across the predefined lengths of coastline, we treated these blocks of coastline as a fixed effect, while annual trend (slope) was modeled as a random effect to account for variation in annual trend across blocks of coastline. Results were similar between the entire time series or the most recent and more complete time series . In general, numbers of wintering black ducks in Nova Scotia increased (1.0-16.0%/y) and increases were significant (Bayesian credible intervals did not bound 0) in four of five regions. Increasing numbers in Nova Scotia are consistent with other observations of increasing wintering numbers at the northern range of American black ducks and may indicate a shift in the wintering range that has been ongoing for decades. Future habitat management actions will benefit from consideration of regional trends and the distributional change of black duck.

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Section: Discussionmentioning

confidence: 97%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Increases in the Number of American Black Ducks Wintering in Nova Scotia, 1970–2015

Robertson

Tomlik

Milton³

et al. 2017

Journal of Fish and Wildlife Management

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“…While fewer black ducks wintering in the TNWR may be related to a shift in the species' range (Link et al 2006, Brook et al 2009, National Audubon Society 2013, it is unclear what factors might be influencing this shift (e.g., climate change, habitat quantity and quality, competition with Mallards). Newcomb (2014) reported potential differences in habitat use between surviving and dying black ducks, but this comparison was limited by a paucity of mortalities.…”

Section: Resultsmentioning

confidence: 99%

“…Research into factors possibly influencing declines in black duck populations is especially important in the Mississippi Flyway, where the steepest declines have occurred. Changes in black duck populations have not been uniform throughout the species' range, and both breeding and winter survey data reveal contrasting population trends, with declines in southern, western, and central sectors of the range, but stabilization or slight increases in northeastern areas (Link et al 2006, Brook et al 2009, Zimmerman et al 2012). There was a 2-fold decrease in the MWS population index for black ducks in the Atlantic Flyway between 1955 and 2014 (582,453 to 269,000 birds), while the index for the Mississippi Flyway showed a 9-fold decrease during the same period (178,400 to 19,700 birds; Fronczak 2012, USFWS 2014).…”

Section: Introductionmentioning

confidence: 99%

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2016

The Condor

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Long‐term changes in autumn–winter harvest distributions vary among duck species, months, and subpopulations

Verheijen,

Webb,

Brasher

et al. 2024

Ecology and Evolution

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Our aim was to describe shifts in autumn and winter harvest distributions of three species of dabbling ducks (blue‐winged teal [Spatula discors], mallard [Anas platyrhynchos], and northern pintail [Anas acuta]) in the Central and Mississippi flyways of North America during 1960–2019. We measured shifts in band recovery distributions corrected for changes in hunting season dates and zones by using kernel density estimators to calculate 10 distributional metrics. We then assessed interannual and intraspecific variation by comparing species‐specific changes in distributional metrics for 4 months (October–January) and three geographically based subpopulations. During 1960–2019, band recovery distributions shifted west‐ and southwards (blue‐winged teal) or east‐ and northwards (mallard and northern pintail) by one hundred to several hundred kilometers. For all three species, the broad (95% isopleth) and core distributions (50% isopleth) showed widespread decreases in overlap and increases in relative area compared to a 1960–1979 baseline period. Shifts in band recovery distributions varied by month, with southward shifts for blue‐winged teal most pronounced in October and northward shifts for mallard and northern pintail greatest during December and January. Finally, distributional metric response varied considerably among mallard subpopulations, including 2–4‐fold differences in longitude, latitude, and overlap, whereas differences among subpopulations were minimal for blue‐winged teal and northern pintail. Our findings support the popular notion that winter (December–January) distributions of duck species have shifted north; however, the extent and direction of distributional changes vary among species and subpopulations. Long‐term distributional changes are therefore complex and summarizing shifts across species, months, or subpopulations could mask underlying finer‐scale patterns that are important to habitat conservation and population management. A detailed understanding of how species distributions have changed over time will help quantify important drivers of species occurrence, identify habitat management options, and could inform decisions on where to focus conservation or restoration efforts.

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Evidence for Black Duck Winter Distribution Change

Cited by 24 publications

References 12 publications

Increases in the Number of American Black Ducks Wintering in Nova Scotia, 1970–2015

Increases in the Number of American Black Ducks Wintering in Nova Scotia, 1970–2015

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Long‐term changes in autumn–winter harvest distributions vary among duck species, months, and subpopulations

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