Point count efficiency and nesting success in marsh-nesting birds (Ontario)

In large coastal and inland emergent wetlands in the Great Lakes basin, southern Ontario, Canada, I investigated the efficiency of point counts based on the Bird Studies Canada Marsh Monitoring Program bird point count protocol to detect species richness and relative abundance, as well as effects of wetland size and water depth on nesting success and the association of nest site habitat preferences and nesting success of marsh-nesting birds. Repeated visits resulted in significant increases in cumulative species richness and total relative abundance up to as many as 9 visits depending on water level, vegetation type and whether aerial foragers were included. Station placement at the edge versus the interior of vegetation patches and observer variability had no effect on within-station species richness. Flushing lines yielded lower species richness compared to point counts. Among wetlands in and around Peterborough, Ontario, size and water depth did not significantly affect nesting success, except success was significantly lower in smaller wetlands during the nestling stage for Red-winged Blackbirds (Agelaius phoeniceus). Nesting success was lower closer to the wetland edge for all species examined, but differences were not significant. Nest site preferences of marsh-nesting birds were not associated with nesting success, except Red-winged Blackbirds who preferred and had significantly better success at nest sites with sparser dead vegetation. Predator composition and the intensive defence of large areas of marsh by Red-winged Blackbirds probably contribute to the weak association between nest site preferences and nesting success in marsh-nesting birds.