Patterns from eBird -- Ivory Gull

Although birders and ornithologists used to speak of "accidentals", the vagrant occurrences of birds are, in fact, anything but random. As more such records have been collected, we have come to understand that bird biology, geography, and weather govern what species occur where, and that even the most improbable vagrant records may have underlying patterns. 

Thanks to help from Joel McNeal, Peter Vickery, Rachel Farrell, and several others, we have compiled a list of historical records of Ivory Gull from the Northeastern United States from 1900-1999. These records revealed the following patterns:

• During the past century Ivory Gulls were only reported in 28 years.

• They occur in winter, usually December to March but with a concentration of records in January and February.

• Not surprisingly, the more northerly states have the lion’s share of records. The most southerly confirmed records in the East had been from New Jersey (four records), the Washington D.C. area (in the late 1800s), and Tennessee (1997).

• Some years with multiple records may represent small-scale “invasions”. Of the 28 years with records, 5 years had two individuals, three occurred in winter 1970-1 and 1980-1, and six (!) occurred in 1939-40.

• the vast majority of historical records have involved immatures; of 55 total records since 1900, 31 have involved first-winters, 12 have involved adults, and for 7 we have no ageing information.

However, during the past decade Ivory Gull vagrancy patterns seem to have changed. From 2000 to 2005, there were just two United States records (Fig. 1) and three from southern Canada (Ontario, New Brunswick, Nova Scotia). But since 2005, a total of twelve Ivory Gulls have been found in the United States with ten from the Northeast, two from the Midwest (South Dakota, Minnesota) and three in southern Canada (British Columbia, Ontario, Nova Scotia); these locations are plotted on the map in Figure 2 and detailed in Table 1.

Fig. 1 and 2. Locations with Ivory Gull records (in green) for 2000-2005 (Fig. 1; upper) and 2006-2010 (Fig. 2; lower). Although darker green indicates a higher frequency of occurrence, usually this is just an indication of how many checklists there are from people who were not chasing this particular Ivory Gull!

These recent records indicate several departures from the historic patterns of Ivory Gull vagrancy. First, Ivory Gulls have appeared in the Northeast in 8 out of the past decade (including annually since 2005), while they were found in only 20 years of the past century. Second, 2009-10 qualifies as the all-time biggest invasion year with six U.S. records and another two from southern Canada. Third, two records have been extremely far south (Cape May, NJ and West Point Dam, GA/AL) and the Cape May record was the earliest well-documented record for the East Coast, first appearing 27 November. Finally, the shift in the age ratios seems particularly alarming: of eleven records in the last two winters, all but one have been adults! The final chapter of the Georgia adult is worth noting. About a week after its discovery, it was found dead and necropsy revealed the cause of death to have been fungal infection in its lungs. This story may be typical of many far-flung vagrants, which perhaps do not survive to breed again successfully.

While birdwatchers enjoying these opportunities to see Ivory Gulls, it’s easy to forget this species has been precipitously declining for decades, that it was listed in 2006 as an endangered species in Canada ( COSEWIC 2006) where only a few hundred breeders remain, and is an IUCN Redlist species. If it is declining so dramatically, then why are we seeing a pattern of increased of winter vagrancy across North America?

Climate change is having a dramatic impact on the flora and fauna of the Arctic and near Arctic. This is leading to a disruption of established patterns of breeding, feeding, and migratory behaviors in many organisms. For example, Black Guillemots (Cepphus grylle) populations in the high Arctic are showing significant declines. Likewise, Polar Bear (Ursus maritimus) populations are threatened as their feeding strategies have been disrupted.

Ivory Gull populations also appear to be changing and the recent surge in vagrant records could also be a signal of more widespread environmental problems in the Arctic. Perhaps an unsettled and less suitable arctic environment is causing these birds to wander more widely in search of food; this might explain the high incidence of vagrant adults in recent records. Whereas past invasions involving immatures may have been partly due to years of high productivity or juvenile survivorship, the more recent records may be being driven by another cause that is more ominous for the species’ long-term future.

Understanding the patterns of species occurrence, both within the core of their range and at the periphery, continues to be essential to conserving bird populations. eBird is playing an ever larger role in documenting and illustrating these patterns, and your contributions will continue to improve our ability to track and understand all bird species.

April is eBird's fundraising month and is just around the corner. If you enjoy these "Patterns from eBird" and other content and new features from eBird (e.g., eBird Alerts), please consider supporting eBird with a donation.

Table 1. Records of Ivory Gulls in the United States and southern Canada from 2005 to March 2010. These records comprise the reports in Fig. 2.

• Rue du Fleuve, Lévis, Quebec. February-March 2010. Adult.
• Cherry Beach, Toronto, Ontario. February 2010. Adult.
  
• Lake Champlain, NY. February 2010. Adult.
• West Point Dam, Troup Co., GA, January 2010. Adult.
• Westport, MA/RI and Newport, RI, January 2010. Adult.
• Race Point, Provincetown, MA, January 2010. Adult.
• Hampton, NH, January 2010. Adult.
• Cape May, NJ, November-December 2009. First-winter.
• Plymouth Harbor, Plymouth, MA, January 2009, Adult.
• Eastern Point, Gloucester, MA, January 2009, Adult.
• Sambro Fish Hatchery, Nova Scotia, January 2009, Adult.
• Oahe Dam, Hughes Co., SD, February 2008, First-winter.
• Canal Park, Duluth, MN, January 2008, First-winter.
• Briggs Pond, RI, December 2007. First-winter.
• Matsqui Flats, British Columbia, November 2007, Adult.
• Piermont Pier, Rockland Co., NY, February 2007, Adult.
• Wheatley Harbor, Ontario, January 2006. First-winter.