Over the next half century the human population is expected to grow rapidly, resulting in the conversion of rural areas into cities. Wetlands in these regions are therefore under threat, even though they have important ecosystem services and functions. Many obligate marsh-nesting birds in North America have shown declines over the past 40 years, and it is important to evaluate marsh bird community response to increased urbanization. We surveyed 20 coastal marshes in southern Ontario, Canada, and found that obligate marsh-nesting birds preferred rural over urban wetlands, generalist marsh-nesting birds showed no preference, while synanthropic species showed a trend towards increased richness and abundance in urban marshes. The Index of Marsh Bird Community Integrity (IMBCI) was calculated for each wetland and we found significantly higher scores in rural compared to urban wetlands. The presence of a forested buffer surrounding the marsh was not an important factor in predicting the distribution of generalists, obligates, synanthropic species, or the IMBCI. More isolated marshes had a lower species richness of obligate marsh-nesters and a lower IMBCI than less isolated marshes. Based on our results, we recommend that urban land use is not the dominant land use within 1000 m from any wetland, as it negatively affects the abundance and richness of obligate marsh-nesters, and the overall integrity of the avian community. We also recommend that all existing wetlands be conserved to mitigate against isolation effects and to preserve biodiversity.
Periodic partial harvesting of trees is an important economic activity within the highly fragmented woodlands of southern Ontario. We studied the population density, age structure, food abundance, productivity, and nest survival of Rose-breasted Grosbeaks (Pheucticus ludovicianus) nesting in 35 deciduous woodlots with varying intensities of harvest. Heavily cut woodlots contained higher densities of territorial males and greater abundances of fruit-bearing shrubs compared with standard cut and reference sites (uncut for >13 years). Results based on insect sampling were mixed, depending on the sampling technique and sample date. All treatments were demographic sinks, with populations in this landscape showing annual declines of 19%24%. Though the proportion of parasitized nests tended to be higher in heavily cut sites, harvesting had little effect on nest survival, nest initiation dates, clutch size, age structure, or the number of young fledged from a successful nest. Our results indicate that within the fragmented woodlots of southern Ontario, partial harvesting does not further degrade breeding habitat for Rose-breasted Grosbeaks. However, further research is needed to determine the underlying causes of population declines.
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 areasensitive 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.
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