Integrating published data and citizen science to describe bird diversity across a landscape

Summary 1. Knowledge of species diversity across a landscape is essential for answering ecological questions and developing conservation and management goals and protocols. However, data on species occurrence are often limited, with the consequence that species lists are incomplete. 2. As a means to develop a complete species occurrence list for an urbanizing landscape in south-eastern Michigan, USA, all bird species accounts from four public and private organizations were integrated, and all officially documented rare birds added. A citizen science approach was then used to develop an independent species list from c. 1700 landowner surveys. 3. The specific goals of the research were to: (i) develop a complete list of species occurrence across a landscape; (ii) ascertain what percentage of the total species pool landowners could collectively identify; (iii) identify species that had not been noted in the census data sets but could be corroborated; (iv) compare the percentage overlap among different bird censuses; and (v) assess the potential value of casual (i.e. citizen science) records to bird distribution studies. 4. The resulting list comprised 318 individual bird species, which was 8·5% greater than any of the individual lists. Landowners identified 171 bird species ( c. 54%) and had > 50% overlap with all existing databases. In addition, landowners identified 10 species noted only in a single database of rare or vagrant species. The percentage overlap of species across the five different lists ranged from 35% to 66%, with the differences stemming largely from different protocols. Subsetting the data for one county within the landscape reduced the unique species to 294, which was approximately equivalent to the existing county species list. 5. Synthesis and applications . The findings highlight the value of surveying private landowners as a means of detecting species presence/absence in numerous inaccessible locations, and the important role landowners can play in providing species occurrence information. Similarly, the results indicate the need to use multiple data sources for establishing a list of potential species occurrence for the conservation and management of biological resources.