TY  - RPRT
TI  - Population trends of black ducks and mallards from the North American Breeding Bird Survey: Are increases in mallards associated with declines in black ducks?
AU  - J.R. Sauer
AU  - Sam Droege
PY  - 1997
UR  - https://pubs.usgs.gov/publication/5211120
ID  - 5211120
ER  -