Monitoring Mercury in Forsters Terns: A Dual Life-Stage Approach to Assessing Effects and Toxic Thresholds Collin Eagles-Smith 1 and Josh Ackerman 2 1 U.S. Fish and Wildlife Service, Sacramento 2 U.S. Geological Survey, Davis

Central nervous system effects Altered behavior Impaired vision, hearing, and motor skills Endocrine effects Embryo death Embryo deformities Chick death Waterbirds Represent a Sensitive Endpoint for Mercury Toxicity

Bird Mercury Concentrations Blood [THg] (ppm ww) Forsters tern Caspian tern Avocet Stilt Surf scoter Avian LOAEL

Avocet Stilt Caspian tern Forsters tern Percent of Population at Risk Breeding Birds Only Low RiskModerate RiskHigh RiskExtra High Risk 6% 5% 10% 58% Risk Factor: High + Extra High * Based on breeding adult blood Hg concentrations

Forsters Tern Habitat Use

Developing Monitoring Tools Need to be: Indicative of local exposure. Reflective of recent exposure. Linked to population-level effects. Logistically feasible. Insert photo egg/chick in nest

Study Objectives Obj. 1: Determine egg toxicity thresholds for: –1a. Abandonment –1b. Hatchability Obj. 2: Determine effects threshold of egg-derived mercury on chick mortality. Obj. 3: Link mercury concentrations in eggs to those in down feathers.

Linking Mercury to Effects: A Conceptual Model Trophic Transfer Maternal Transfer Fail-to-Hatch Hatch Mortality (<10 d) Survive Incubation Abandon (Obj. 1A) (Obj. 1B) (Obj. 2)

Linking Mercury to Effects: A Conceptual Model Maternal Transfer Fail-to-Hatch Hatch Mortality (<10 d) Survive Abandon

Project Update Terns have arrived and began initiating nests at South Bay breeding grounds. Nest monitoring underway at 5 separate colonies. Chicks will begin hatching in ~4 weeks

Egg Micro-Sampling Pilot Study Drill tiny hole in shell. Sub-sample albumin. Seal shell hole. Analyze albumin Link Hg to individual egg hatchability.

Mercury in Micro-Sample versus Whole Egg (mallard eggs)

Linking Mercury to Effects: A Conceptual Model Trophic Transfer Maternal Transfer Fail-to-Hatch Hatch Mortality (<10 d) Survive Incubation Abandon (Obj. 1A) (Obj. 1B) (Obj. 2) (Obj. 3) Egg Hg Abandonment Egg Hg Hatchability Egg Hg Chick Survival Egg Hg Effects

Littoral Foragers – eat insects & crustaceans American avocets Black-necked stilts Obligate Piscivores – eat fish Forsters terns Caspian terns Species Studied Benthic Foragers – eat bivalves Surf scoters

Avocets & Stilts Forsters Terns

Mercury in Eggs Extra High High Risk Category Low North Bay Central Bay South Bay Egg [THg] (ppm dw) Moderate Avocets Stilts Forsters Terns

New Chicago Marsh Eden Landing Ecological Reserve Mercury as Chicks Age: Stilts Culmen Length (mm) (age) Blood [THg] ( g g -1 ww) Hatch Fledge

Mercury as Chicks Age: Stilts and Terns Forsters terns Hatch Fledge Stilts

Chick Survival: Stilts & Avocets Newly Hatched