Implications of the Species-Area Relationship on Sampling Effort for Marsh Birds in Southern Ontario

Coastal wetlands of southern Ontario are highly fragmented and exist as islands within a primarily urbanized and agricultural matrix. Given the large variation in size of remaining fragments, it is important to determine if species-area relationships exist for wetland birds, so that sampling effort can be adjusted for different sizes of wetlands and to develop appropriate size criteria for conservation. We surveyed marsh birds in 21 coastal wetlands of southern Ontario and found a positive species-area relationship (z-value = 0.076), and a positive relationship between an index of biotic integrity and wetland area. Only the Marsh Wren, Swamp Sparrow, and all obligate wetland bird species combined showed area-sensitive distribution patterns. The number of points required to reveal 80% or 90% of the cumulative species richness for a given wetland varied directly with its size, indicating that sampling effort must be increased to avoid underestimating species richness in large wetlands. For example, one would need to conduct 9 point counts using 50-m radius circular plots to survey 90% of the wetland bird species in a marsh of 50 ha. We recommend conservation of coastal wetlands, regardless of size, because both small and large marshes provide habitat for high-integrity, wetland-dependent bird species.