Abundance, distribution, and species assemblages of colonial waterbirds in the boreal region of west-central Manitoba and east-central Saskatchewan

Central and southern Manitoba contain some of the largest breeding populations of several colonial waterbird species in North America. Despite the value of this region for waterbirds, very little monitoring has been conducted on Lake Winnipeg, Lake Winnipegosis, or Lake Manitoba in the past three decades and little is known about the smaller boreal lakes in adjacent areas to the north. In June 2011, boat surveys were conducted on 11 boreal lakes in west-central Manitoba and east-central Saskatchewan to examine current abundance and distribution of colonial waterbirds in that region. Data from this survey were compared with abundance of colonial waterbirds on Lake Winnipegosis and Lake Manitoba from an aerial survey of these lakes in 2012. Waterbird colonies were located on 7 of the 11 lakes in 2011 and included Double-crested Cormorants (Phalacrocorax auritus) (2373 adults, 1134 pairs in 7 colonies), Common Terns (Sterna hirundo) (1367 adults, 772 pairs in 29 colonies), Forster’s Terns (Sterna forsteri) (20 adults, 11 pairs in 1 colony), Herring Gulls (Larus argentatus) (876 adults, 568 pairs in 23 colonies), and Ring-billed Gulls (Larus delawarensis) (3752 adults, 16 colonies). Common Terns and Herring Gulls appeared to be predominantly breeders and pair abundance for both species increased in a sigmoidal fashion; lakes <100 km2 in area had few breeding pairs. Numbers of Double-crested Cormorants and especially, Ring-billed Gulls, may have included a sizeable non-breeding component. Densities (pairs/lake area) of Common Terns and Herring Gulls were about 2 and 4 times higher, respectively, on these lakes than on Lake Winnipegosis and Lake Manitoba, while Double-crested Cormorant and Ring-billed Gull densities were higher on lakes Winnipegosis and Manitoba. Additional studies of productivity in relation to lake characteristics and connectivity among colonies throughout the region would further our understanding of the importance and sustainability of waterbird populations in this region of the boreal forest