Assessing Climate Change Vulnerability of Breeding Birds in Arctic ...

AdTundra Swan (Cygnus columbianus)Vulnerability: Presumed StableConfidence: HighThe Tundra Swan is the more widespread and northerly ranging of the two native swan speciesin North America. In Arctic Alaska, they nest in wet to dry tundra habitat types preferring islandsin lakes or ponds, or naturally occurring frost heaves at the intersection of polygon pond rims.Nesting territories almost always include a large lake that the family will use as a safe havenfrom terrestrial predators (Limpert and Earnst 1994). During the breeding season, their diet isprimarily vegetarian, eating emergent and submerged vegetation in lakes and ponds. They alsograze on terrestrial vegetation near the water (Limpert and Earnst 1994). Most North Slopebreeders winter on the east coast Mid-Atlantic States (Limpert and Earnst 1994). The currentArctic Coastal Plain population is estimated at approximately 10,000 (Larned et al. 2012).E. WeiserRange: We used the extant NatureServe rangemap for the assessment as it closely matched theBirds of North America and other rangedescriptions (Johnson and Herter 1989, Bart etal. 2012).Human Response to CC: Human activities inresponse to climate change, in particular,shoreline fortification against erosion couldimpact Tundra Swans as they sometimes usenear coastal areas for resting and foraging duringmigratory staging (Limpert and Earnst 1994).However, such activity will likely be localizedin the near future so it was considered to slightlyincrease vulnerability, if at all.Physiological Hydro Niche: Tundra Swans wereranked as particularly vulnerable to changes inhydrologic niche because of their dependence onlakes for breeding and molting (to avoidpredation) and aquatic vegetation (for foraging).Non-breeding flocks also rely heavily on lakes.If substantial drying occurs, this species couldexperience a considerable negative impact.Current projections of annual potential evapotranspirationsuggest negligible atmosphericdrivendrying for the foreseeable future (TWSand SNAP), and atmospheric moisture, as anexposure factor (most influential on the“hydrological niche” sensitivity category), wasnot heavily weighted in the assessment.However, its interaction with hydrologicprocesses is very poorly understood (Martin etal. 2009).Disturbance Regime: Climate-mediateddisturbance events, namely thermokarst, couldboth create and destroy good foraging andnesting habitats through both ice wedgedegradation and draining of thaw lakes (Martinet al. 2009). Likewise, predicted increased stormfrequency (Jones et al. 2009) could reduceavailability of their primary forage(submerged/emergent vegetation) as waterturbulence in bays and rivers could increase (S.Earnst, pers. comm.).Biotic Habitat Dependence: Tundra Swansdepend on Arctophila grass for brood-rearingcover thus the “biotic habitat dependencecategory” was considered a source ofvulnerability. The broad range of responses inthis category (from “neutral” to “greatlyincreased” vulnerability) reflects the uncertainty40