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4. Threats

The most important threat to Ivory Gulls is illegal shooting in Greenland (COSEWIC2006), but other factors such as predation on nests, industrial activity, contaminants, human disturbance due to monitoring, climate change and oil pollution also have the potential to negatively affect Ivory Gull populations (see Table 1).

4.1 Threat Assessment

Table 1: Threat Assessment Table. Accessible version of Table 1
ThreatLevel of Concern1ExtentOccurrenceFrequencySeverity2Causal Certainty3
Biological Resource Use
Illegal shootingHighLocalizedHistoric, CurrentSeasonalHighMedium
Changes in Ecological Dynamics or Natural Processes
Predation on nestsHighLocalizedCurrentSeasonalHighHigh
Disturbance or Harm
Industrial activitiesMediumLocalizedCurrent, anticipatedSeasonalMediumLow
Human disturbance - monitoringLowLocalizedHistoric, Current, AnticipatedSeasonalLowMedium
Pollution
ContaminantsMediumWidespreadHistoric, Current, AnticipatedContinuousMediumLow
Oil pollutionLowLocalizedHistoric, Current, AnticipatedContinuousUnknownHigh
Climate and Natural Disasters
Climate changeLowWidespreadCurrent, AnticipatedContinuousUnknownLow

1 Level of Concern: signifies that managing the threat is of (high, medium or low) concern for the recovery of the species, consistent with the population and distribution objectives. This criterion considers the assessment of all the information in the table.

2 Severity: reflects the population-level effect (High: very large population-level effect, Medium, Low, Unknown).

3 Causal certainty: reflects the degree of evidence that is known for the threat (High: available evidence strongly links the threat to stresses on population viability; Medium: there is a correlation between the threat and population viability e.g. expert opinion; Low: the threat is assumed or plausible).

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4.2 Description of Threats

1. Illegal shooting

As a long-lived bird with low annual reproductive output, Ivory Gulls rely on high annual survival of adults to maintain their population. As such, mortality of adults can greatly reduce the overall population size, and thus human harvest of adults is a serious problem (Stenhouse et al. 2004). In Greenland, subsistence, sport and commercial harvest of numerous species of birds, many of which are birds that breed in Canada, still occurs. Ivory Gulls are susceptible to hunting mortality (Stenhouse et al. 2004), because they fly along coastlines during migration where other marine birds are being hunted. In particular, Ivory Gulls from Canadian colonies are shot in Greenland (Neilsen and Dietz 1989), despite being protected in that country since 1977. Based on banding records, most of these birds are shot during spring or fall migration, or on their way to or coming from Canadian colonies (Stenhouse et al. 2004). Currently, in Canada subsistence harvest by Inuit is minimal (Priest and Usher 2004; M. Mallory pers. comm.) and probably has negligible effect on populations. Although 20% of interviewees in Newfoundland and Labrador reported hunting Ivory Gulls in the past, hunting during winter rarely occurs nowadays (Ryan et al. 2006).

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2. Predation on nests

Ivory Gulls appear to choose extremely remote nesting locations to avoid predators (Haney and MacDonald 1995). If predators are encountered (e.g. polar bears, Arctic foxes, common ravens Corvus corax), gulls have few defenses to stop predation. Consequently, colonies can be decimated in a single season (MacDonald 1976). In Canada, there is no other wildlife observed near Ivory Gull colonies on the Brodeur Peninsula (Baffin Island), or on the nunataks of eastern Devon and Ellesmere islands (Gilchrist and Mallory 2005, Mallory et al. 2008). In two (2002, 2009) of six years of surveys at Seymour Island, virtually no birds were counted at the large colony (generally > 100 birds), presumably due to predation (Gilchrist and Mallory 2005, M. Mallory, unpubl. data). In two other years (2007, 2008), predators hit the island and consumed all but a few of the eggs (M. Mallory, unpubl. data). Polar bears have been seen regularly there, and they are probably the main predator at that colony. Changes in ecological dynamics and natural processes due to industrial activities and climate change may lead to increased predation rates.

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3. Industrial activities

Ivory Gulls are apparently tolerant of brief colony visits, but like many other colonial birds may be less tolerant of repeated visits, such as would occur near industrial sites. The community of Arctic Bay has been particularly concerned that industrial activities might be affecting nesting birds and other wildlife in northern Baffin Island. Activities near such sites include the placement of fuel caches, gravel landing sites for fixed-wing air craft, seasonal camps, and drilling sites. The one breeding area in Canada near industrial activity (diamond exploration on the Brodeur Peninsula) also happens to be the area where a formerly robust breeding population (> 500 birds) has effectively disappeared (Gilchrist and Mallory 2005, Robertson et al. 2007). Establishment of industry (e.g. mining) in the Arctic also tends to attract predators (COSEWIC2006), which can decimate gull colonies.

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4. Contaminants

Contaminants deposited in the Arctic by long-range transport are a potential threat to the health of many wildlife species living there (Fisk et al. 2005). Ivory Gulls may be particularly susceptible because they forage high in the food chain. Ivory Gull eggs have the highest mercury concentration of any Arctic bird (Braune et al. 2006), and have high levels of other organic contaminants (Buckman et al. 2004, Braune et al. 2007, Miljeteig et al. 2009). Although studies have not been performed directly on Ivory Gulls, other Arctic gulls show negative effects on reproduction, behaviour, development, immunology and on their genetic structure at lower contaminant concentrations than found in Ivory Gulls (Gabrielsen 2007).

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5. Human disturbance - monitoring

Some researchers and Inuit communities (e.g., Grise Fiord) have suggested that visits by researchers to colonies could have caused declines through disturbance during the nesting season. Haney and MacDonald (1995) suggested that Ivory Gulls were sensitive to ground and air traffic near their colonies. Evidence from Canada and Norway suggests that this is probably not always the case. In these two countries, colonies have been visited briefly by helicopter, at which time some of the gulls leave the cliffs but quickly return to their nests (< 1 minute; COSEWIC2006). Similarly, researchers camped on an island with an Ivory Gull colony for several years in the 1970s, and the gull population returned in good numbers each year to breed. Nonetheless, there may be a threshold level of disturbance that is important, below which gulls are tolerant, and above which they abandon breeding for the year, or possibly the colony site. This requires further investigation to confirm.

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6. Climate change

Warming temperatures are affecting the distribution, timing of formation and break up, and extent of sea-ice in Baffin Bay (e.g., Stirling and Parkinson 2006), such that ice tends to be less extensive, forms later and breaks up earlier than in the past. Such a strongly ice-associated species might be faced with challenges when encountering less extensive ice, and ice cover for shorter periods, somewhat analogous to the situation with polar bears (Stirling and Parkinson 2006). Similarly, the core of the current, known breeding population of Ivory Gulls is in the nunatak region of east-central Ellesmere Island. Depending on the configuration of the nesting location, melting (receding) glaciers (a consequence of global warming) may have two effects at nesting sites: (1) direct breaking off of ice can physically alter or destroy a nesting site; and (2) increased rock and ground cover revealed by receding glaciers may allow other species to flourish (e.g. vegetation and lemmings, Dicrostonyx spp.), which in turn makes it likely that predators will be able to access currently remote breeding locations.

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7. Oil pollution

Chronic oil pollution off of Newfoundland and Labrador kills many marine birds every year (Wiese and Robertson 2004). This region includes part of the known wintering area of the Ivory Gull (Haney and MacDonald 1995). Gulls are considered to be highly vulnerable to oil pollution (Camphuysen 1998), and thus Ivory Gulls are probably affected, although to date no carcasses have been found. This could in part be related to the offshore location where the gulls reside relative to areas where people might find dead birds.