Many of the winter bird population studies that were used in this paper were undertaken through the Toronto Bird Observatory, quite a few years ago when I was on the Board. Quite a few volunteers were involved in that work. In addition the paper also used historical data collected by many prominent birders in the Toronto area.
You can find an abstract of the paper, as well as the full text here.
Great work Paul! And thanks for letting us know. It's great to see published work using data from volunteers - especially TBO volunteers!
Paul also mentioned that he has previously published an article in the Canadian Field Naturalist (Volume 117, Number 2, Apr–Jun 2003) titled "Winter Bird Use of Urban and Rural Habitats in Ontario", which uses some of the same data. Unfortunately, this article is not available online.