Changes in Canadian seabird populations and ecology since 1970 in relation to changes in oceanography and food webs

Abstract

Systematic monitoring of seabird populations in Canada has been ongoing since the 1920s and the monitoring of diets and other biological indicators of ecosystem change started in the 1970s. Long-term monitoring of population parameters began in the 1980s. These studies originally were conducted mainly by the Canadian Wildlife Service, but subsequently have involved several universities and nongovernment organization groups. We review the results of this monitoring from the 1970s onwards for six oceanographic regions to assess population trends among Canadian seabirds and correlated trends in diets, phenology, and other breeding biology variables. Within regions, trends in most variables studied have been broadly congruent, but there was often variation among regions. In particular, seabird populations in the Pacific coast zone affected by the California Current upwelling system have shown generally negative trends since the 1980s, whereas trends for populations of the same species to the north of this zone have been mainly positive. Likewise, on the east coast, trends at Arctic colonies have been decoupled from those at colonies around Newfoundland and in the Gulf of St. Lawrence, especially since the major cold water event of the early 1990s. Several long-term studies have shown an association between population events and diet and phenology changes. Diet and indicators of condition (chick growth, reproductive success) sometimes responded very rapidly to oceanic changes, making them excellent signals of ecosystem perturbations. The review highlights the effects of decadal-scale regime shifts on Canadian seabirds, confirms the value of long-term studies and supports the applicability of single-site observations to regional populations.

Key winter habitat of the ivory gull Pagophila eburnea in the Canadian Arctic

“…Approximate historic hooded seal whelping locations (small black circles) and bounds (large hollow circles) as described in Sergeant (1974), Orr & Parsons (1982), Bowen et al (1987) and Stenson et al (1996). These correspond well to the overlapping area in Davis Strait of wintering satellite-tagged ivory gull individuals breeding on colonies in Canada and Norway and observations of wintering ivory gulls by at-sea surveys (PIROP, 1969(PIROP, −1992 birds are there, and continuing research on the wintering distribution and behaviour of seabirds in the northwest Atlantic will help us understand how ivory gulls and other seabirds may be affected by anthropogenic disturbances of this region of the Arctic (Gaston et al 2009), and aid in the development of appropriate conservation measures to actively address threats in areas identified.…”

Inter-annual variability in diet of non-breeding pelagic seabirds Puffinus spp. at migratory staging areas: evidence from stable isotopes and fatty acids

“…The cause of this shift is unknown but transitions in seabird diets in other regions have been linked to changes in food webs driven by changes in oceanographic conditions (Montevecchi 2007). This may include very broad-scale oceanographic regime changes that alter the prey base (Hare & Mantua 2000, Gaston et al 2009). Such shifts associated with warm waters in the Northwest Atlantic have been linked directly with the increase of warm-water prey, such as mackerel and squid, in the diets of seabirds (Montevecchi & Myers 1995).…”

Postbreeding dispersal and staging of Common and Arctic Terns throughout the western North Atlantic

“…In the western North Atlantic, from southern Labrador, Canada (52° N) to Cape Cod, Massachusetts, USA (41° N), the breeding ranges of Common (Sterna hirundo) and Arctic (S. paradisaea) Terns overlap and the two species nest sympatrically on nearshore and offshore islands (Kress et al 1983, Gaston et al 2009). The wintering ranges of these populations are geographically separated, with Common Terns wintering along the coasts of Central and South America (Hays et al 1997, Nisbet et al 2011a, and Arctic Terns wintering along the Antarctic pack ice (Hatch 2002).…”