Introduction This book summarizes the results of Ontario's second breeding bird atlas project. A second breeding bird atlas is quite a different undertaking from a first atlas. The second brings with it the built-in excitement of comparing the distribution of every nesting species to a standard data set collected using the same methodology employed 20 years earlier. The results not only provide a fully up-to-date assessment of the distribution and status of every species that nests in the province but also allow scientists to assess changes that have occurred over the intervening period. Both results are of great value to conservationists and researchers interested in the province's birds and the ecosystems that support them. But the second Ontario atlas project brought more. We decided not only to repeat the first atlas but to follow the lead of Maryland, Britain, Switzerland, Holland, and others, adding in a system of counting birds that would allow us to produce maps of the relative abundance of many species. This was a big decision, requiring extra preparation and work by the province's birders, but they rose to the occasion splendidly and the results speak for themselves, as you will see throughout this book. The point count data have allowed us to map the relative abundance of many species throughout the province for the first time, so we can see where each species is most abundant and can assess how its abundance varies with environmental features. The point count data also provide an invaluable base of comparison for future atlases. Repeating these point counts in 20 years' time during the third atlas will allow an assessment of how the relative abundance of each species has changed across the province and of the importance of various factors that might have contributed to those changes. The point count data also allowed us to produce estimates of the population size of many species in Ontario. The estimates and the methodology used to produce them are provided in Appendix 5. The overall goals of the second atlas were to: 1. Repeat the 1981-1985 atlas to provide detailed maps of each species' distribution in Ontario and to compare those with the first atlas to show changes in distribution. 2. Collect abundance data to allow contour mapping of the relative abundance of many species and to provide a baseline for comparison with future atlases. 3. Record information on the location of breeding sites of significant species. 4. Get people out into the field to enjoy themselves birding while contributing to an important conservation project. 5. Produce a book and a database available for research and conservation purposes. Field data collection was carried out during the five-year period of 2001-2005. Data were collected throughout the province. In addition, as in the first atlas, data were collected on several islands in James and Hudson Bay that are part of Nunavut, particularly Akimiski Island in James Bay where the OMNR has a field station and actively collects data annually. Coverage on Akimiski Island was more extensive during the second atlas than during the first. Because of the close biogeographic relationship of these islands with the Hudson Bay Lowlands, the results were combined with those from the Hudson Bay Lowlands region throughout the book. The "Methods" chapter of this book provides details of how the data were collected. Briefly, volunteer participants were asked to spend time in at least one 10 kilometre (km) by 10 km square ("10-km square"), listing bird species present and recording evidence for breeding on a standard data form. Those able to identify birds by song and call were also given the option of collecting information on the relative abundance of species by doing point count surveys. Generally, the atlas project met its coverage goals, which is a great credit to the 3,417 participants listed in the Acknowledgements section of this book and to the atlas' sponsoring and supporting organizations. Ontario is a very large tract of bird habitat (1,068,587 square kilometres), stretching from Middle Island in Lake Erie (at about the same latitude as Rome and northern California) to the northern hemisphere's most southerly tundra habitat on the subarctic shores of Hudson Bay. The chapter "Biogeography of Ontario" explains more about the ecological and land-use characteristics of the province, providing background for understanding the distribution and abundance patterns shown on the atlas maps. "Coverage and Results -- An Overview" summarizes the coverage obtained and key results. The chapter entitled "Changes in Bird Distribution between Atlases" compares the results of the two atlas projects and assesses why some of the changes revealed might have taken place. Prior to reading species accounts and viewing the species maps and tables, we recommend that you read the chapter entitled "Interpreting Species Accounts," which explains the various maps and graphs and the format and structure of the written species accounts. Of course, the species accounts, with the maps of distribution and relative abundance for each species, are the heart of the book. Each of the 286 species (plus two hybrids, Brewster's and Lawrence's Warblers) for which breeding evidence was reported during the second atlas is given a two-page account. At the end of the section is a brief accounting of the other species for which breeding evidence has been reported in Ontario at some time other than during the second atlas -- primarily historical breeders. Following the species accounts are various appendices providing more detail on other aspects of atlassing and of the book itself. Both the Ontario Breeding Bird Atlas project and this book were made possible through the support and involvement of the province's birders. We trust that all readers, and particularly those who contributed data, will enjoy the fruits of their labour as portrayed here. Additional information about the atlas project is available on the atlas web site, www.birdsontario.org. Excerpted from Atlas of the Breeding Birds of Ontario, 2001-2005 by Michael D. Cadman All rights reserved by the original copyright owners. Excerpts are provided for display purposes only and may not be reproduced, reprinted or distributed without the written permission of the publisher.