Effects of vegetation characteristics and time-since mowing on nest-site selection and nest survival of Savannah Sparrows (Passerculus sandwichensis) in Western New York

Abstract

Since the 1970s grassland bird populations have been declining. The main causes of the decline include habitat loss and degradation. This decline has led to the need for more information on what habitat characteristics are needed for grassland birds to successfully breed and how management practices impact breeding success. Our objective was to determine the nesting habitat preferences of Passercu/us sandwichensis (Savannah Sparrows) and how nest-site characteristics, along with mowing practices influence the probability that a nest will fledge young (nest survival). We conducted this study over an 8-week period at John White Wildlife Management Area in Basom, New York. We searched for Savannah Sparrow nests using behavioral cues and monitored them every 2-3 days to determine nest fate. Vegetation characteristics at each nest along with a corresponding random point were measured. We also gathered data on the history of mowing practices at each field within our study site and measured the distance each nest and random point was from both hard edges (forest) and soft edge (agricultural fields and roads). We found and monitored 21 Savannah Sparrow nests. The probability that a nest survived a single day was 0.951 (95% CI [0.911, 0.980]). We found that nest visibility index within a 1-meter radius of the nest was the only variable that significantly affected nest-site. Vertical vegetation density at 5-meters from the nest had a significant positive effect on nest survival and was the only vegetation factor that influenced nest survival. Time­ since mowing did impact nest survival where daily nest survival rate was greater in fields that had not been mowed since 2'.: 8 months or longer. We found that as distance from soft edge increased daily nest survival rate increased, but distance to either edge type (hard or soft) did not affect survival. The results we found could be used to help managers create high quality habitat for Savannah Sparrows in Western New York.