From linthicum: "European Starlings are among the worst nuisance species in North America. The birds travel in enormous flocks; pose danger to air travel; disrupt farms; displace native birds; and roost on city blocks. Corrosive droppings on structures cause hundreds of millions of dollars of yearly damage."
2nd Place with 78 points:
From DonnaB: "The Mandarin a Native of China is found in private collections & Zoo's. They are the only related bird to the U.S. native Wood Duck. Escapees compete with our native cavity nesters such as Wood Ducks & Hooded Mergansers. There is a feral population of several 100 Mandarins in Sonoma County, Ca."
3rd Place with 77 points:
From ginger749: "This Picture was taken in Queensland, Australia.
Crested Pigeon Ocyphaps lophotes
Runner Up with 69 points:
From LNinOH: "I live in NE Ohio, Zone 5b. This picture was taken on Friday, March 11, 2011, showing the non-native House Sparrow (Passer domesticus) competing with a native Cardinal at one of my feeders. I have had a flock of about 27 house sparrows all winter."
Runner Up with 62 points:
From DeboTracewell: "A hummingbird having a little bathtime. Villa Park, CA Zone 10"
Runner Up with 61 points:
From linthicum: "The Mute Swan has been widely viewed as an invasive species because of its rapidly increasing numbers (doubles in 7-8 years) and its impact on other waterfowl and native ecosystems. Always controversial, Mute Swans are protected in some areas of the U.S. by local laws, for example, in Connecticut."
Runner Up with 34 points:
From DaylilySLP: "Mallard (Anas platyrhynchos). The same pair comes every Spring and hangs out in our Pond. We allow them to stay 2 weeks, then begin chasing them away."