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

Abstract

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.

Historical and Current Population Trends of Herring Gulls (Larus argentatus) and Great Black-Backed Gulls (Larus marinus) in the New York Bight, USA

“…Several factors have the potential to influence (or more importantly bias) estimates of breeding pairs (or nests) within gull colonies during ground or aerial surveys. Seasonal and individual (bird) variation in the amount of time both members of a breeding pair spend at the nest site can be an important issue (Hanssen 1982;Wilson 2013). Also, the presence of juvenile and non-breeding adult gulls in Laridae nesting colonies has the potential to bias (i.e., result in overestimation of) the estimated number of breeding pairs of birds within colonies (Hanssen 1982;Rodgers et al 2005;Green et al 2008;Washburn 2013).…”

Lake Use by Three Avian Piscivores and Humans: Implications for Angler Perception and Conservation

“…In contrast, these same human activities (shoreline development and recreational boating) may be directly responsible for the decline of more sensitive avian piscivores. Development often results in the loss of near-shore emergent vegetation, which is important nesting habitat for various grebes, gulls, herons, and terns [13,14]. Disturbance by humans has been well documented to cause nest site abandonment by colonial birds [9,15], and boating can disrupt parent-chick associations (e.g., grebes) resulting in elevated juvenile mortality [16].…”