Mallards have been replacing Black Ducks in human-altered landscapes in Ontario, 1996-2019

The American Black Duck (hereafter Black Duck) has received much attention over the years as a popular game bird species that experienced historical declines on its wintering grounds. Declines may be due to changes in the quality and quantity of breeding habitat, competition with Mallards, or both. Although the Black Duck population has stabilized, spatial variation in regional population trends of Black Ducks on their breeding grounds can provide insight into the relative importance of these alternative hypotheses at provincial and local scales. We analyzed indicated breeding pairs count data collected in Ontario between 1996 and 2019 through the Eastern Waterfowl Survey to evaluate the correlation in breeding densities and trends of the five most abundant waterfowl species. We also tested whether habitat and anthropogenic disturbance variables could explain the distribution of those species. Overall, Mallard breeding pair densities increased across the survey area, while Black Duck br..., Waterfowl dataThe waterfowl data have been collected through the The Eastern Waterfowl Survey (EWS). A breeding waterfowl survey that has been conducted annually since 1990 by CWS in an area extending from northeastern and central Ontario east through central and southern Quebec, New Brunswick, Nova Scotia, Newfoundland, and southern Labrador. Each spring between late-April and early-June, observers counted and identified ducks and geese observed on every waterbody, watercourse, and wetland within a 25-km2 square survey plot using a helicopter.
All waterfowl observations were identified to species, sex, grouping and numbers (e.g., lone or paired birds, flocked, etc.) and georeferenced to a location or waterbody. These observations were used to infer the number of Inidcated Breeding Pairs (IBPs) according to the standardized method developed by the Black Duck Joint Venture for helicopter surveys in Eastern Canada. The full methodology for the survey and the IBPs calculatons are desc..., , # Mallards have been replacing Black Ducks in human-altered landscapes in Ontario, 1996-2019

[https://doi.org/10.5061/dryad.pg4f4qrzt](https://doi.org/10.5061/dryad.pg4f4qrzt)

## Description of the data and file structure

### Files and variables

#### File: Acronyms\_Key.csv

**Description:** 

##### Variables

* Variable name: Identify the acronyms used in the data file
* Description: Contain the full name of the species or the landscape variable

#### File: habitat\_scaled.csv

**Description:** 

##### Variables

* numericplot: numeric identifier for each plot
* Region: the Region to which the plots have been assigned
* aOMS: Proportion of the area in the plot covered by emergent vegetation
* aTMS: Proportion of the area in the plot covered by treed wetland
* pWAT: Perimeter open waterbodies in kilometers 
* aWETL: Proportion of the area in the plot covered by wetlands
* pWETL: Perimeter of wetlands in kilometers 
* aBUI: Proportion of the area in the plot covered by infrastructure...