Colony Dynamics and Persistence of Ivory Gull Breeding in Canada

Abstract

ABSTRACT. Despite the importance of assessing the viability of small and endangered populations, often few demographic data are available. However, when counts are available from discrete sites, a colony-or site-based approach can be useful. We used recent counts of Ivory Gull, Pagophila eburnea, a rare species that breeds at remote sites in the high Arctic, to model colony dynamics and population persistence. Colonization rates were low at 0.189 ± 0.054 (mean ± SE), new colonies were small (mean: 7.7 pairs), and there was no evidence of local rescue effects from nearby colonies. Based on these rates, a population projection model was constructed using a starting population of 225 pairs at the 24 sites. The projected population reached an equilibrium of approximately 30 pairs in only 8 yr. The large and isolated colony on Seymour Island has declined at 2.7%/yr (95% confidence limits: -13.9, 8.5) since 1974, and had low but wide-ranging probabilities of going extinct within 20 yr. The suggestion that Ellesmere Island may be the only site where breeding Ivory Gull will persist in the future is supported by the recent discovery of new colonies there in 2006.RÉSUMÉ. En dépit de l'importance d'évaluer la viabilité de petites populations en voie de disparition, il existe souvent peu de données démographiques. Toutefois, lorsqu'on dispose de dénombrements pour des sites isolés, une méthode d'analyse par colonie ou par site peut s'avérer utile. Nous avons utilisé des dénombrements récents de Mouettes blanches, Pagophila eburnea, une espèce rare qui se reproduit dans des sites reculés dans le Haut-Arctique, pour modéliser la dynamique des colonies et la pérennité des populations. Les déclins importants observés dans le nombre de couples nichant au Canada sont à l'origine de l'attribution nouvelle du statut « en voie de disparition » à l'espèce par le Comité sur la situation des espèces en péril au

Status of the endangered ivory gull, Pagophila eburnea, in Greenland

“…In fact, earlier studies have shown that for the ivory gull, the number of breeding adults reported from single censuses of a colony (e.g. all Greenland census presented in Table 1) is close to the total number of breeding pairs using the colony, hence advocating the use of a two-fold correction factor (Mallory et al 2008;Robertson et al 2007;H. Strøm, personal communication 2009).…”

“…The likely decline in southern colonies can be compared with recent trends reported for Canadian colonies (Gilchrist and Mallory 2005;Mallory et al 2003;Robertson et al 2007). In Canada, the 80% decline documented over a period of 20 years has been hypothesized to have resulted mainly from pollution and excessive hunting (e.g.…”

“…Periodic non-breeding, a common feature in Arctic birds (Bertram and Roberts 1934;Bird and Bird 1940;Marshall 1952), including the ivory gull Robertson et al 2007;Volkov and Korte 2000), is another obstacle to assess past and future population trends. Indeed, it is diYcult to assess the true population trends in ivory gull colonies from the year of discovery because, by deWnition, the initial census is always positive, while subsequent censuses can be positive or null.…”

Time series data for Canadian arctic vertebrates: IPY contributions to science, management, and policy

“…Long-term monitoring of arctic vertebrate populations has been essential not only for developing policy and regulating harvest Peacock et al 2010;Higdon et al 2011), but also for input to international climate change analyses (Arctic Climate Impact Assessment ACIA 2005), regional land use planning and environmental assessment (Mallory and Fontaine 2004), and downlisting/uplisting species (Stirling and Parkinson 2006;Robertson et al 2007). Funding and logistical support during IPY made significant contributions to longterm time series for arctic vertebrates, including the standardization of metadata, establishment of long term archives and improving access to collected data.…”

New Longevity Record for Ivory Gulls (<i>Pagophila eburnea</i>) and Evidence of Natal Philopatry

“…The Seymour Island Migratory Bird Sanctuary in Nunavut (76.80˚ N,101.27˚ W) includes a small island supporting one of the largest remaining breeding colonies of ivory gulls known in Canada (Robertson et al, 2007). As part of a study to investigate the dispersal patterns and overwintering areas of ivory gulls, we flew to Seymour Island on 30 June 2010.…”