Western (Aechmophorus occidentalis) and eared (Podiceps nigricollis) grebes of central Alberta: 2004 field summary
Berg, G.; Wilkinson, L.; Wollis, H.; Prescott, D.
Alberta Species at Risk Report, 94 i-vi, 7-23
2004
Accession: 024132933
This project is in its fourth year and is designed to monitor population trends and reproductive success of western grebes and eared grebes within the Stony Plain, Alberta area. Surveys are projected to span a five-year period, and the results are being used for conservation and management efforts. Western grebes are the priority species because they are provincially listed as "sensitive". This project also provides information to support lake habitat conservation and public education. In 2004, surveying effort was focused on the primary western and eared grebe populations identified in the previous years of this project. Ground nest surveys were conducted after the nesting period, the results of which were used to derive a total breeding adult population estimate. In addition, surveys were initiated in the Parkland region in 2004, to identify waterbodies that supported potential western grebe breeding colonies. We estimated the population of western grebes in the Stony Plain study area to be appr. 1270 adults, much lower than in 2003 (2554 adults), and lower than all previous years of study. Generally, nesting colony locations were similar to previous surveys. Western grebes inhabiting Wabamun Lake and Lac Ste. Anne continue to be the dominant populations in the study area, representing 54.1% and 26.3% of the regional population, respectively. Since 2003, the Wabamun Lake colony decreased in size by nearly 53% (likely due to high rates of corvid nest depredation), and the Lac Ste. Anne colony decreased by 72%. These colonies were formerly considered nationally significant due to their size, but are now considered only regionally significant. The Isle Lake population is the only colony that grew in size, doubling from 2003. Western grebes appear to return each year to historical breeding sites on large lakes, and are vulnerable to human disturbance, making site protection essential. In particular, critical reed habitat for nesting colonies is being cleared as a result of human development. In 2004, eared grebe colony searches were conducted on fifteen lakes. Eared grebes were observed on nine lakes, for a conservative overall population estimate of 8865 adults. Only seven of these lakes had breeding colonies, and three of these lakes supported the aforementioned western grebe colonies. The number of eared grebes observed in 2004 was higher than all previous years of study, including a dramatic increase from 2003 (up from 1880+). This increase can be attributed to a colony found on Majeau Lake (3594+ adults), in a part of the lake that was not surveyed previously. For the fourth consecutive year, George Lake supported the largest eared grebe population in the study area; numbers increased significantly from 2003 but are slightly lower than 2002 surveys. Eared grebe population sizes and colony locations appear to be highly variable, suggesting that they rely on a network of waterbodies to sustain their regional population. Eared grebes appear to prefer shallow and undeveloped lakes and generally avoid waterbodies with extensive boating. This is the first year for surveys in the Parkland Region of Alberta. Initial results found that of the eleven lakes surveyed, nine supported populations of western grebes, with the largest populations being located on Buffalo and Gull lakes. Although no evidence of breeding activity was recorded, surveys in future years will focus on trying to identify colonies and confirm breeding. Expanding western grebe colony surveys throughout the province will provide valuable information for status evaluation and conservation.