Changes in Populations of Nesting Seabirds on the Bird Islands, Cape Breton, Nova Scotia

Abstract

The Bird Islands support the largest colonies of nesting seabirds in Nova Scotia. From a continental perspective the islands host one of the largest Great Cormorant (Phalacrocorax carbo) colonies in North America and a significant Razorbill (Alca torda) colony. However the islands are best known for nesting Atlantic Puffins (Fratercula arctica). Populations of all species have changed over the past 75 years, none so dramatically as Black-legged Kittiwakes (Rissa tridactyla). Kittiwakes colonized the islands 20 years ago and are now the most numerous nesting seabirds. Two other recent colonists, Herring (Larus argentatus) and Great Black-backed Gulls (L. marinus) are the next most common nesting species on the islands. In contrast the small colony of Common Murres (Uria aalge) and the large colonies of Arctic (Sterna paradisaea) and Common Terns (S. hirundo) of the 1920s have disappeared. Here we present recent estimates of breeding populations and summarize the data on changes in populations in the past 75 years based on a review of the literature, and surveys conducted from boats circumnavigating the islands during 11 different years from 1976 until 2000. The changes in breeding populations of seabirds on the Bird Islands show that their importance for conservation has changed through the years. For example in the 1920s about one third of all nesting Double-crested Cormorants in Nova Scotia were on the Bird Islands. In 1933 no Great Cormorants nested on the islands. In contrast in 2000 they supported the largest colony of Great Cormorants in North America and less than 1% of the Double-crested Cormorants in eastern Canada.