Short communication Declines in abundance and distribution of the ivory gull (Pagophila eburnea) in Arctic Canada H. Grant Gilchrist a, * , Mark L. Mallory b a Canadian Wildlife Service, Prairie and Northern Region, National Wildlife Research Centre, 1125 Colonel By Drive, Raven Road, Carleton University, Ottawa, Ont., Canada K1A 0H3 b Canadian Wildlife Service, Prairie and Northern Region, Box 1714, Iqaluit, Nunavut, Canada X0A 0H0 Received 1 December 2003; received in revised form 22 April 2004; accepted 30 April 2004 Abstract The ivory gull (Pagophila eburnea) is a seabird that inhabits Arctic oceans throughout the year, often in association with polar pack ice. It is rare (<14,000 breeding pairs globally) and remains one of the most poorly known seabird species in the world. Canada supports breeding populations of international significance, and residents of communities in the Canadian High Arctic currently observe fewer ivory gulls than they did in the 1980s. However, no population trend data existed for this species in Canada prior to this study. We initiated aerial surveys in July 2002 and 2003 of most known ivory gull colonies in Canada to assess current pop- ulation levels. Forty two colonies were visited, 14 of which were new discoveries. We recorded an 80% decline in numbers of nesting ivory gulls. Several of the largest known colonies were completely extirpated and those that remained supported significantly fewer nesting birds than previously observed. Results were similar in both years despite some differences in local sea ice conditions, suggesting a numerical decline in the population and not simply annual fluctuations in colony occupation. Declines have occurred in all habitat types and across the known Canadian breeding range, suggesting that causes of the decline may be related to factors occurring during migration or on wintering grounds. We recommend that international efforts now be directed at assessing pop- ulation status and trends of this species in other circumpolar countries. Crown Copyright Ó 2004 Published by Elsevier Ltd. All rights reserved. 1. Introduction Marine birds are effective indicators of the health of marine ecosystems (Cairns, 1987; Nettleship and Duffy, 1993), and in the Arctic, these ecosystems appear to be changing (Etkin, 1990; Stern and Heide-Jørgensen, 2003). Fluctuations in marine bird populations or breeding success often signify shifts in the physical or biological characteristics of marine environments (e.g., Furness and Nettleship, 1991). While some of these changes have been observed in marine birds with large populations (e.g., Gaston, 2003; Montevecchi and Myers, 1997), the effects on species with small popu- lations are more poorly known and of greater conser- vation concern. For example, the ivory gull (Pagophila eburnea) is an uncommon species that feeds in associ- ation with sea ice throughout the year (Haney and Macdonald, 1995; Stirling, 1997), and it may be par- ticularly sensitive to changes in sea ice cover known to be occurring in Arctic oceans (Etkin, 1990; Roots, 1989; Vinnikov et al., 1999). Moreover, both its pop- ulation size and distribution in North America appear to have been shrinking since the late 1800s (Haney and Macdonald, 1995). The ivory gull is a small, pure white gull that spends the entire year in circumpolar marine environments. Compared to other marine birds, little is known about this species (Haney and Macdonald, 1995). Canada was thought to support approximately 6–10% of the global breeding population (14,000 pairs; Anker-Nilssen et al., 2000), representing nesting colonies of continental and international importance. The ivory gull was assigned * Corresponding author. E-mail addresses: grant.gilchrist@ec.gc.ca (H. Grant Gilchrist), mark.mallory@ec.gc.ca (M.L. Mallory). 0006-3207/$ - see front matter. Crown Copyright Ó 2004 Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.biocon.2004.04.021 Biological Conservation 121 (2005) 303–309 www.elsevier.com/locate/biocon BIOLOGICAL CONSERVATION