Monitoring Mercury in Forster’s Terns: A Dual Life-Stage Approach to Assessing Effects

and Toxic Thresholds

Collin Eagles-Smith1 and Josh Ackerman2

1U.S. Fish and Wildlife Service, Sacramento2U.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 ConcentrationsB

loo

d [

TH

g]

(pp

m w

w)

Forster’s tern

Caspian tern

Avocet Stilt0.01

0.1

1

10

Surfscoter

Avian LOAEL

Percent of Breeding Population at Risk

0 20 40 60 80 100

Avocet

Stilt

Caspian tern

Forster’s tern

Percent of Population at RiskBreeding Birds Only

Low Risk Moderate Risk High Risk Extra High Risk

6%

5%

10%

58%

Risk Factor:High + Extra High

* Based on breeding adult blood Hg concentrations

Forster’s 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 TransferFail-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)

Egg Hg (ug/g ww)

0.1 1 10 100

Alb

um

in H

g (

ug/g

ww

)

0.1

1

10

100

R2=0.96

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

Ab

and

on

men

t

Egg Hg

Hat

chab

ility

Egg Hg

Ch

ick

Su

rviv

al

Egg Hg

Eff

ects

Littoral Foragers – eat insects & crustaceans• American avocets• Black-necked stilts

Obligate Piscivores – eat fish• Forster’s terns• Caspian terns

Species Studied

Benthic Foragers – eat bivalves• Surf scoters

Avocets & Stilts Forster’s Terns

Mercury in Eggs

Extra HighHigh

Risk Category

Low

0.1

1

10

North Bay

Central Bay

South Bay

Eg

g [

TH

g]

(pp

m d

w)

Moderate

Avocets Stilts Forster’s Terns

New Chicago Marsh

Eden Landing Ecological Reserve

Mercury as Chicks Age: Stilts

10 20 30 40 50 60

Culmen Length (mm)(age)

Blo

od [

TH

g] (g

g-1 w

w)

5

1

0.1

Hatch Fledge

New Chicago Marsh

Eden Landing Ecological Reserve

10 20 30 40 50 60

Culmen Length (mm)(age)

Blo

od

[TH

g]

(g

g-1

ww

)

5

1

0.1

Hatch Fledge

Mercury as Chicks Age: Stilts and Terns

Chick Age (days)0 10 20 30 40

Ch

ick

Blo

od

Mer

cury

(u

g/g

ww

)0.1

1

10

Forster’s terns

Hatch Fledge

Stilts

10 20 30 40 50 60

Culmen Length (mm)(age)

Blo

od [

TH

g] (g

g-1

ww

)

5

1

0.1

Hatch Fledge

Chick Survival: Stilts & Avocets

Newly Hatched

0.1

1.0

10.0

100.0

Avocet StiltC

hick

dow

n fe

athe

r [T

Hg]

(µ

g g-1

fw)

Live chicksDead chicks

Newly Hatched