Preliminary study of impacts of a large roosting bird congregation on a pest exclusion fenced area of Rotopiko wetland ecosystem

This pilot study aims to quantify the impacts of roosting birds on the pest exclusion fenced area of Rotopiko wetland ecosystem in the Waikato region of New Zealand. Water samples were collected from five monitoring stations, encompassing four stations within the fenced area (three along a drain running through the fenced area into the lake, and one from the fenced lake itself), and one from a nearby unfenced lake, not affected by roosting. Soil samples were collected from three monitoring stations: two inside the fenced area, with varied roosting density, and one outside. Sampling was conducted once in each season, during winter (August 2021), spring (November 2021) and summer (February 2022). For each sampling time, a triplicate sample was taken at each station. Within the fenced area, increased nutrient loading in water and soil, and microbial growth in water, were observed in areas with the highest roosting pressure. Water tested where the drain enters the lake showed an up to 44-fold increase of total nitrogen, a 750-fold increase in faecal coliforms, and a 915-fold increase in Escherichia coli compared to water collected at the point where the drain enters the fenced area. Comparison between the lakes showed that the total nitrogen concentration in the fenced lake was 16 times higher than in the non-fenced lake, while the number of faecal coliforms and E. coli were over 30 times higher at the fenced lake. This study, although limited in sample size and statistical power, sheds light on the impacts of roosting birds on the Rotopiko ecosystem.