Habitat use of spectacled eider broods in relation to salinity and food availability on the Yukon-Kuskokwim Delta, Alaska

Abstract

Spectacled eiders (Somateria fischeri) nest and raise their broods in coastal areas of the Yukon-Kuskokwim Delta, which may be vulnerable to projected climate change effects of increased temperatures, storms, and sea level rise. These changes in turn will likely affect wetland salinity levels used by ducklings, which are a potential constraint to growth and survival of young ducklings while their salt glands develop. To examine this potential concern, I investigated spatial and temporal pond salinity dynamics, food availability, and habitat use of spectacled eider broods at Kigigak Island, AK during 2011-2012. I found that salinity was highly variable across the island, ranging from 0-23.9 ppt and averaged 4.9-12.9 ppt in ponds at brood observation sites during the first 30 days of brood rearing. Salinity typically increased through the summer across all habitat types, but at the highest rate in high sedge habitat. The most common invertebrate taxonomic groups included Eurytemora, Harpacticoida, Annelida, and Chironomidae, which were found in nearly all ponds sampled with salinity ranging from 0.7- 16.1 ppt. Neither salinity nor invertebrate abundance explained pond foraging use by broods. Additionally, I used robust design occupancy models to estimate brood foraging patterns. Pond occupancy ranged from 0.43-0.59 between years. Overall, brood use of ponds was not dictated by salinity levels or invertebrates present, suggesting that most ponds provide suitable brood rearing habitat. I did not detect any obvious constraint to pond use within brood rearing habitat under the environmental conditions encountered.