A comparison of the bird communities of two high country lakes

A study was undertaken to document and compare the aquatic bird communities of two high country lakes, Lake Pearson and Lake Grasmere, located in the Cass Basin, Waimakariri Valley, Canterbury. The two lakes show differences in shoreline structure, riparian communities and humun use patterns. Lake Pearson is regularly used by people for recreation while Lake Grasmere is a Wildlife Refuge and recreation activities are restricted. Data is gathered on bird abundance and feeding activity over the course of eleven months. The bird communities of these lakes showed differences in species composition and abundance within their community structure with Lake Pearson exhibiting greater species richness and Lake Grasmere greater abundance. These differences were the result of many interactions occurring between lake morphology and component aquatic and terrestrial vegetation, season and life cycle influences and human disturbances to the lakes. Species demonstrated different responses to these factors. Extensive aquatic macrophytes in Lake Grasmere attract large abundances of waterfowl, particularly Black Swans and Canada Geese. The latter species has the potential to significantly add to the nutrient loading of the lake. Species composition and abundance were also influenced by season, with some bird species migrating away from the lakes to escape the harsh winter or to travel to breeding grounds. Lake Grasmere is important as a moulting site for waterfowl, particularly Paradise Shelduck and as a feeding habitat for the threatened species, crested Grebe. Lake Pearson is an important breeding habitat for Crested Grebe but experiences regular disturbance from human recreation