Mercury Contamination in the Common Yellowthroat (Geothlypis

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EFFECTS OF MERCURY CONTAMINATION ON INDIVIDUAL QUALITY

AND CONDITION OF COMMON YELLOWTHROATS (GEOTHLYPIS TRICHAS)

A University Thesis Presented to the Faculty

California State University, East Bay

In Partial Fulfillment

of the Requirements for the Degree

Master of Science in Biology

Deanna de Castro

June, 2014

ABSTRACT

Historic mines in New Almaden, CA such as the New Almaden Quicksilver

Mine (NAQM), are a source of mercury contamination throughout South San

Francisco Bay, California. Mines in this area drain into the Coyote Creek (CC) and Guadalupe River (GR). Water quality and sediment assessments for mercury show increasing levels with increasing proximity to the New Almaden.

Tellingly, birds captured at upper GR and CC had some of the highest reported concentrations of mercury in the feathers and blood within the United States.

Thus, organisms living within the riparian habitats along the CC, GR, and their tributaries may be affected by local environmental mercury. This study investigates of the feather mercury from Common Yellowthroats (Geothlypis trichas) caught at varying distances from NAQM and the relationship between feather mercury and of body condition and individual quality. Birds in upper

GR and CC and at Llagas Creek had higher mass, primary wear, and rectrice wear compared to birds in lower CC and GR. Bib size and fluctuating asymmetry of barbule density in rectrices was greater in birds located in CC and

GR. Hue of bib feathers was significantly greater in birds caught at lower GR and CC and upper CC. Total mercury concentrations in rectrices were highest in birds caught in upper GR. All comparisons were significant with a p-value of less than or equal to 0.05.

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EFFECTS OF MERCURY CONTAMINATION ON INDIVIDUAL QUALITY

AND CONDITION OF COMMON YELOWTHROATS (GEOTHLYPIS TRICHAS)

Deanna de Castro

Approved: Date:

______Dr. Caron Inouye

______Dr. Danika LeDuc

______Dr. Erica Wildy

ACKNOWLEDGEMENTS

I would like to express my gratitude to my advisor, Dr. Caron Inouye, for providing invaluable advice and insight on my project and academic and professional career. Thank you to Drs. Danika LeDuc and Erica Wildy for their guidance on the chemical and ecological facets of my research. Also, I would like to thank my entire committee for their patience and encouragement when I was struggling most.

Many thanks to SFBBO’s Josh Scullen and Jill Demers for their generosity and advice for a successful field season. Thank you to Ryan BourBour, Corey

Clatterbuck, Allison Greggor and Breanna Martinico for enduring those early mornings with me.

Thank you to MPSL’s Jessica Masek and Wes Heim. MPSL very kindly offered their help and equipment in order for me to analyze my feathers.

I would also like to thank Dr. Ed Pizzini for his advice on analytical chemistry and mercury assays. Thanks to Bill Roan and Sharon Horgan for procuring materials for my analyses and encouragement. Thank you Sherita

Black and Kristian Salcedo for helping me with my image analysis.

Last but not least, I would like to thank my family and Kala Wong for their support and love.

TABLE OF CONTENTS

ABSTRACT...... iii

ACKNOWLEDGEMENTS ...... v

LIST OF FIGURES...... viii

INTRODUCTION ...... 1 Overview ...... 1 Biochemistry and environmental behavior of mercury ...... 3 Physiology of methylmercury ...... 9 Mercury contamination in Santa Clara Valley, CA...... 10 Effects of environmental contamination in passerine birds ...... 13

PURPOSE OF STUDY ...... 19

METHODS ...... 21 Field site selection ...... 21 Sample collection ...... 24 Sample processing ...... 25 Image analysis ...... 26 Feather mercury analysis ...... 28 Morphometric and statistical analysis ...... 28

RESULTS ...... 31 Primary and rectrice feather wear ...... 31 Fluctuating asymmetry of barbule density ...... 31 Bib area and bib hue ...... 32 Structural size ...... 39 Total mercury in feathers ...... 39

DISCUSSION ...... 43 Primary and rectrice feather wear ...... 43 Fluctuating asymmetry of barbule density ...... 44 Bib area and bib hue ...... 46 Structural size ...... 47

CONCLUSION ...... 49

LITERATURE CITED ...... 52

APPENDIX ...... 64

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LIST OF FIGURES

Figure 1. A simplified diagram of the mercury biogeochemical cycle...... 8

Figure 2. Mercury biogeochemical cycling in a lake watershed ...... 8

Figure 3. Map of streams and associated tributaries ...... 12

Figure 4. Diagram of avian tarsus ...... 15

Figure 5. Diagram of a wing chord ...... 15

Figure 6. Map of field sites in relation to one another and nearby cities ...... 23

Figure 7. Illustration of parts of a feather ...... 27

Figure 8. Primary wear score and rectrice wear by stream location ...... 34

Figure 9. Primary wear score and rectrice wear by field site ...... 35

Figure 10. FA of barbule density in rectrice feathers ...... 36

Figure 11. Bib area of birds by stream locations and field site...... 37

Figure 12. Bib hue of birds by stream location and field site ...... 38

Figure 13. Structural size of birds by stream location and field site ...... 41

Figure 14. Total Hg in feathers of birds by stream location and field site ...... 42

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INTRODUCTION

Overview

Awareness of environmental contamination by mercury occurred in the

1950’s when people living and working in Minamata Bay, Japan became sick with what became to be known as Minamata disease. The Minamata Research

Group recognized that the disease was related to consumption of marine plants and animals. Villagers in the area began observing strange behaviors from fish, birds, and cats. In particular, cats would have difficulties walking and suffer from convulsions. These same symptoms were experienced by people with

Minamata disease in addition to sensory and auditory disturbances, tunnel vision, and tremors (Harada, 1995). The cause of Minamata disease was determined to be methyl-mercury (MeHg) exposure after examination of the affected cats and from efforts identifying past medical conditions with similar symptoms shown by those in Minamata Bay in previous literature (Harada,

1995).

The source of the MeHg was identified to be from the Chisso Minamata industrial plant which was using mercury as a catalyst. The plant had been dumping waste into the Minamata Bay and neglected to investigate potential impacts of the dumped chemicals on the environment. As a result, mercury had

accumulated over decades in food items that supplied the village (Grandjean,

Satoh, Murata, & Eto, 2010; Harada, 1995; Wright, 2001).

Another epidemic of human mercury poisoning through environmental mercury contamination occurred in 1971 in Iraq. MeHg had been used as a fungicide since around 1914. The chemical had been adopted by developing countries for this use in the 1940’s-1960’s, again, without monitoring its impact on the environment (Grandjean, et al., 2010; Wright, 2001). People were exposed to mercury after eating wheat products made from MeHg-treated wheat that was intended for seeding crops. Dissemination of the tainted seed occurred in

September 1971. 6,530 cases of MeHg poisoning had been admitted to hospitals over the following half-year, beginning in January 1972 (Bakir et al., 1973;

Wright, 2001).

The means of exposure for both epidemics were very different. People were exposed to relatively low concentrations of MeHg over many years in the

Minamata case as a result of biomagnification, or the concentration of a toxicant within higher trophic levels (Connell, 2009 ). Conversely, the 1971 Iraqi grain incident quickly exposed the populace to extremely high levels of MeHg. In both cases, the cause of the exposure was due to contaminated food items. For humans, the determining risk factor for mercury toxicity is the amount and type of food in the diet. However, determining the mercury toxicity risk factor for

wildlife is less straightforward considering the difficulty of assessing the true diet patterns of wildlife (Wright, 2001).

Human activities have influenced the mercury cycle which may have caused increased transformation of various mercury species into the more toxic

MeHg form. Though mercury and its related compounds have been used for a variety of applications since around 2000 B.C., two-thirds of the mercury on the surface of the earth has been mined in the twentieth century. Furthermore, about

30-40% of the total annual flux of mercury into the atmosphere can be attributed to anthropogenic sources (Amos, Jacob, Streets, & Sunderland, 2013; Fitzgerald &

Clarkson, 1991). Mercury emitted through human activities can later be recycled and re-deposited in the atmosphere and contribute to natural sources due to the ease with which mercury can change form. Thus, the actual source of environmental mercury can be obscured (Wright, 2001).

Biochemistry and environmental behavior of mercury

Mercury can be found in three different states in the environment; however, none of them have a known biological function. These states are as follows: elemental mercury (Hg (0)), divalent mercury (Hg (II)), and organic forms of mercury -- such as MeHg. Elemental mercury is liquid and quickly volatilizes at room temperature. It is the major form of mercury in the atmosphere. Hg (II) ionizes easily to create mercury salts and is highly soluble in

water. MeHg is an organic form of mercury and is highly toxic compared to other species of the element. Monomethylated mercury has low water solubility and is more stable than dimethylated mercury (Methylmercury, 2000; Wright,

2001). Additionally, MeHg is somewhat lipid soluble as a result of its low water solubility (Methylmercury, 2000). Because of these properties, MeHg is highly toxic and can accumulate in organisms (Fitzgerald, Lamborg, &

Hammerschmidt, 2007).

Most sources of mercury are found in the form of a mineral deposit known as cinnabar. Mercury from cinnabar is mobilized into the atmosphere through weathering or volcanic activity and eventually deposited in deep-ocean sediment (Rytuba, 2003; Selin, 2009). The total length of time mercury cycles between volatilization in the atmosphere to deposition in ocean sediment has been calculated to be between 3000 and 10,000 years (Selin, 2009).

Anthropogenic activities -- such as burning of fossil fuels, mining, and industrial processing – liberate mercury from long-term storage. As a result, the amount of mercury currently in cycle has significantly increased (Fitzgerald & Clarkson,

1991; Selin, 2009).

The biogeochemical cycle of mercury can be divided into three pathways of exchange: atmospheric processes, terrestrial cycling, and aquatic cycling (Fig.

1). Hg (0) in the atmosphere is oxidized to Hg (II), the mercury species

associated with particulates. Deposition from the atmosphere typically occurs with Hg (II) due to its higher water solubility than Hg (0). After deposition, 5-

60% of Hg (II) may re-volatilize back into the atmosphere, while the remainder is stored in organic matter in surface sediments or biomass, e.g., Hg (II) uptake by plants from contaminated rainwater. The portion that is immediately recycled into the atmosphere has a greater tendency to form MeHg (Selin, 2009).

Mercury can be released from terrestrial soil after reduction to Hg (0). Hg reduction occurs through both abiotic and biotic processes. Sterilized samples of soil liberated Hg(0) when microbial activity was stimulated in laboratory conditions. Microorganisms can reduce Hg(II) directly to detoxify their substrate or indirectly by creating substances that directly bind to (decomposed organic matter) or reduce Hg(II) (humic and fulvic acids) (Fritsche, Obrist, & Alewell,

2008). Abiotic reduction of mercury occurs through burning of organic matter

(specifically coal and fossil fuels) by anthropogenic means or ecological processes

(periodic forest fires) can also release mercury into the environment (Selin, 2009).

Understanding the behavior of mercury in aquatic systems is especially important for preserving the health of nearby ecosystems and urban areas because mercury methylation occurs in these environments (Selin, 2009). The aquatic mercury cycle occurs somewhat differently in marine than in freshwater systems (Fig. 2). Freshwater systems receive mercury through wet and dry

deposition. The majority of the mercury that enters freshwater systems is in the form of Hg (II). Hg (II) in freshwater can be reduced to Hg (0) as in terrestrial systems. However, a small quantity of freshwater Hg (II) is converted into

MeHg. Mercury species found in aquatic systems are Hg (0), Hg (II), and colloidal/particulate mercury. Deposition of mercury in aquatic systems occurs in the same manner as freshwater systems, although concentrations of each species vary between different oceans. Transformation of mercury from Hg (II) to Hg (0) or MeHg occurs mainly at the surface through biotic mediation as well as through photo-chemical mediation. Mercury cycling at the surface of the ocean occurs quickly and can extend the time mercury is cycled before long-term storage in deep-ocean sediment (Selin, 2009). Agriculture, large population centers (>50,000 people), previously flooded wetland, and reservoirs located upstream of a sampling site tend to increase the methylation of Hg(II) into MeHg

(Robinson et al., 2011).

Hg (II) in freshwater systems is converted into MeHg by sulfate or iron reducing bacteria either in the water column or sediments. MeHg conversion occurs readily in wetland, lake, and marsh habitats (Christopher H. Conaway,

Black, Grieb, Roy, & Flegal, 2008; C. H. Conaway, Watson, Flanders, & Flegal,

2004; Selin, 2009). There is currently little consensus on methylation processes and locations in marine systems. Estuarine and continental shelf sediments,

water column, and hydrothermal vents are areas of interest for mercury methylation in marine systems (Selin, 2009). In estuaries, mercury methylation is mediated by sulfate reducing bacteria (Christopher H. Conaway, et al., 2008).

Phytoplankton bioaccumulate MeHg when it is expelled into the water column.

Once introduced into the food web through contaminated phytoplankton, biomagnification of MeHg occurs (Christopher H. Conaway, et al., 2008).

As demonstrated by the discovery of Minamata Disease and the 1971 Iraqi grain poisoning, MeHg is a dangerous toxicant that can easily bioaccumulate and biomagnify in higher trophic levels (Bakir, et al., 1973; Harada, 1995; Robinson, et al., 2011). After these incidents, regulation of mercury emissions from point sources increased. By the 1980s, incidences of occupational and point source mercury contamination have been greatly reduced (Wright, 2001). Nevertheless, the flux of mercury in its biogeochemical cycle has been dramatically affected by anthropogenic influences (as discussed above). As a result, MeHg exposure to the environment and wildlife has increased since the industrial revolution.

Accordingly, focus on this form of mercury and its interaction with ecosystems and wildlife has increased.

Figure 1. A simplified diagram of the mercury biogeochemical cycle. From (Tewalt, Bragg, & Finkelman, 2001)

Figure 2. Mercury biogeochemical cycling in a lake watershed. Abbreviations: Hg (0), elemental mercury; Hg (II), divalent organic mercury; MeHg, methylmercury; Resup, resuspension. From (Selin, 2009)

Physiology of methylmercury

Studies in San Francisco Bay have found that phytoplankton more readily take up MeHg than any other organic or inorganic mercury species (Luengen &

Flegal, 2009). Yet, bioaccumulation of MeHg in invertebrates, such as filter- feeding bivalves, was found to be relatively low as a possible result of MeHg dilution in algal blooms (Christopher H. Conaway, et al., 2008; Luengen & Flegal,

2009). However, intermediate trophic fish species (e.g., mosquito fish, Gambusia affinis and redear sunfish, Lepomis microlophus) had MeHg assimilation efficiencies of between 86-94% of bioavailable levels, indicating biomagnification of MeHg within the trophic system (Pickhardt, Stepanova, & Fisher, 2006).

MeHg enters cells by forming a complex with the thiol group of cysteine amino acids after ingestion of contaminated food items. The resulting molecule mimics the properties of methionine and can be transported across cell membranes and into the blood stream through amino acid carriers. Elimination of MeHg occurs in the liver where the MeHg-cysteine complex is reduced to a

MeHg-glutathione complex and secreted into bile. Though around 90% of MeHg is removed via feces, the MeHg-glutatione complex is catalyzed into the MeHg- cysteine complex which is then reabsorbed into the blood stream (Clarkson &

Magos, 2006).

MeHg’s association with the amino acids cysteine and glutathione allow high mobility of MeHg throughout an organism’s body by mimicking membrane carrier substrates (Clarkson & Magos, 2006; Magos, 1997). Consequently, mercury can be distributed in many different tissues, such as: central nervous system tissues (e.g. brain and spinal cord), integumentary tissues (e.g. skin, hair, and feathers), blood, lungs, and kidneys (Magos, 1997). The relatively high water solubility of mercury, however, prevents the toxicant from accumulating in fatty tissues (Clarkson & Magos, 2006). MeHg can also be excreted via vertical transmission, i.e., through eggs, sperm, and fetuses. In mammals for example,

MeHg easily passes through placental barrier through a mechanism similar to

MeHg passage through the blood-brain barrier (Clarkson & Magos, 2006; Magos,

1997). Consequently, MeHg contamination can have longer term consequences on reproductive success (J. Ackerman, Takekawa, Eagles-Smith, & Iverson, 2008;

J. T. Ackerman, Eagles-Smith, Takekawa, & Iverson, 2008; Hopkins, Willson, &

Hopkins, 2013).

Mercury contamination in Santa Clara Valley, CA

Large amounts of mercury were extracted from the northern California coast between 1846 and 1981. Mined mercury was typically used for gold mining, agricultural, and industrial uses (chloralkali processing, pesticides, antifouling paint (Christopher H. Conaway, et al., 2008)). Mercury sourced from

this area amounted to 88% of the total mercury extracted in the United States.

Leaching of mercury from closed mines continue to increase mercury concentrations in streams and other water bodies downstream (Jay A. Davis, Yee,

Collins, Schwarzbach, & Luoma, 2003). Mercury mining in New Almaden,

California is the largest contributor to mercury contamination in the California

Coast (Christopher H. Conaway, et al., 2008; C. H. Conaway, et al., 2004; Jay A.

Davis, et al., 2003; M. A. Thomas et al., 2002).

The New Almaden Quicksilver Mine (NAQM) provides a historic source of mercury contamination to the Santa Clara Valley, CA (Fig. 3). The mines in

New Almaden mining district flow into the Guadalupe River and Coyote Creek

Watersheds (C. H. Conaway, et al., 2004). In the Guadalupe River, sediment concentrations of total mercury and MeHg increase with proximity to the historic mining area. However, total mercury levels in Guadalupe River were measured to be significantly higher than in Los Gatos Creek (M. A. Thomas, et al., 2002)

aroon circles denote cities; orange diamond denotes New Almaden, CA; location of New Almaden location of diamond CA;denote New denotes New Almaden cities; Almaden, orange circles aroon

Figure 3. Map of streams and associated tributaries investigated in this study. Legend: green line, Coyote line, green Legend:ininvestigatedCoyote this study. Figure Map 3. of associated tributaries and streams Llagas line, white Calero blue Creek; line, Creek; Alamitos line, pink River; Creek;Guadalupe line, yellow Creek; m (GoogleEarth, Quicksilver2013b). Mine.

In a study conducted by the San Francisco Estuary Institute, Song

Sparrows (Melospiza melodia) caught at Upper Guadalupe River had the highest levels of blood MeHg in the San Francisco Bay area (Robinson, et al., 2011).

Additionally, feathers of a number of waterbirds and seabirds caught in Alviso

Slough had higher levels of mercury in their feathers relative to aquatic birds in other areas of the United States (J. Ackerman, et al., 2008; J. T. Ackerman, et al.,

2008). Thus, birds living within Santa Clara Valley may have feather mercury levels that reflect mercury levels in their habitat.

Effects of environmental contamination in passerine birds

Mercury exposure can have a number of effects on birds, including increased fluctuating asymmetry (FA) in bilateral morphological features, decreased carotenoid coloration of the plumage, hematocrit level, increased investment in constitutive innate immunity, and overall body condition. These measurements are indicative of relatively poor individual quality and condition in various ways (Joshua T. Ackerman et al., 2012; Berglund & Nyholm, 2011;

Tom Dauwe & Eens, 2008; T. Dauwe, Janssens, & Eens, 2006; Eeva et al., 2000;

Sillanpaa, Salminen, & Eeva, 2010).

FA is defined as random deviations in symmetry in bilateral morphological characteristics, such as length of wing chord or tarsi (Figs. 4 and

5). It can be used as a measurement for developmental instability which can

arise from environmental stress. Causes of stress, such as pollution or decreased food intake, can reduce efficiency of developmental stabilizing mechanisms leading to increased FA (Anciaes & Marini, 2000). Insectivorous birds, like the

Common Yellowthroat (Geothlypis trichas) which is found in the San Francisco

Bay, may have reduced fitness due to FA as body symmetry is important for flight capabilities that enable effective foraging. Also, offspring that exhibit developmental instability through FA may fail to thrive after brood reduction.

(Sillanpaa, et al., 2010). For example, FA of the third primary flight feather in

Great Tit (Parus major) nestlings was greater at field sites nearer to a copper smelter. Fledgling success has been found to be low at this study site due to FA related to poor food availability and resulting brood reduction (Eeva, et al.,

2000). Birds that are able to fledge may not survive long enough to breed.

Interestingly, insectivorous birds in Brazil have been found to be more susceptible to FA (Anciaes & Marini, 2000) compared to their omnivorous counterparts. Thus, it stands to reason that the Great Tit nestlings, which are insectivorous birds, may have been predisposed to the greater third primary FA they exhibited in the earlier study, may not have been able to forage as effectively and were unable to reach breeding age.

Figure 4. Diagram of avian tarsus. Tarsal length is measured using calipers. The leg is held with the tarsus between the thumb and index finger so that it is bent. One jaw of the caliper is used to hold the toes flat so they extend distally while the other jaw is placed at the tibiotarsal joint. Image adapted from (Reichenow, 1913).

Figure 5. Diagram of a wing chord. The wing chord is measured from the point where the wing bends (carpal joint) to the end of the longest primary feather without pressing down or flattening the wing. Image adapted from (Reichenow, 1913).

Carotenoid coloration in the plumage may provide an honest signal of individual condition. Variations in carotenoid coloration may be due to differences in deposition, transport, or metabolism in the feather follicle, which may in turn be affected by stressors (Inouye, Hill, Stradi, & Montgomerie, 2001).

Carotenoids also have antioxidant properties, and birds that have higher plasma concentrations of carotenoids may be better able to respond to oxidative stress.

Therefore, birds with brighter carotenoid coloration may have been better able to allocate resources toward feather quality as opposed to oxidative stressors during molt. Conversely, birds that are exposed to oxidative stressors during molt, such as pollution in their habitat, may be less able to allocate carotenoids toward feather coloration and brightness. This is demonstrated by the fact that

Great Tits express less colorful yellow breast feathers at more polluted sites (Tom

Dauwe & Eens, 2008; Geens, Dauwe, & Eens, 2009). Other species, such as the

Common Yellowthroat, also have large amounts of yellow carotenoid coloration in their feathers, which can be quantified and, thus, used as a potential bioindicator of contaminant exposure in this species. This is significant for this species, because Common Yellowthroats inhabit areas with tall vegetation near water, such as marshes and riparian woodlands/swamps along the rivers in

Santa Clara County, that could be contaminated with mercury from New

Almaden Mining District (Shuford, 2008). Moreover, Common Yellowthroat

carotenoid signals (the yellow bib on males) may signal reproductive fitness to potential mates. Female Common Yellowthroats express preference toward male

Common Yellowthroats with large bibs while in captivity. In addition, male

Common Yellowthroats with large bibs more often acquire a mate and successfully produce offspring from extra-pair copulations (Freeman-Gallant et al., 2010).

Immunotoxic effects of environmental contaminants on free-living birds can illustrate another physiological response. Birds living in areas contaminated with heavy metals must contend with exposure to the pollutant as well as other challenges, such as potentially decreased food availability (T. Dauwe, et al.,

2006). The Great Tit, which has a similar life history to the Common

Yellowthroat, demonstrated reduced constitutive adaptive immune responses

(which includes production of antibodies to an antigen and increased levels of B- and T-cells in circulation) in birds from field sites closer to a source of heavy metal pollution (Snoeijs, Dauwe, Pinxten, Vandesande, & Eens, 2004). Increased ratios of heterophils to lymphocytes are used as measures of constitutive innate immune defenses and have been observed in birds exposed to heavy metals

(Grasman, 2002; Lee, 2006).

It is crucial to understand the impacts of environmental contamination on the condition of these birds, as the San Francisco Common Yellowthroat (G. t.

sinuosa) is a subspecies of special concern that is included in this project

(Shuford, 2008). Another species of concern, the endangered California Clapper

Rail (Rallus longirostris obsoletus) has exhibited deleterious effects from mercury contamination on reproductive fitness and body condition (Joshua T. Ackerman, et al., 2012).

PURPOSE OF STUDY

Because mercury is of great environmental concern and is widely present in the Santa Clara Valley, it is an imperative to understand the extent to which mercury affects the organisms living in the area (J. Ackerman, et al., 2008;

Christopher H. Conaway, et al., 2008; Robinson, et al., 2011). This project is designed to test the hypothesis that total mercury levels in the feathers of

Common Yellowthroats inhabiting areas in the Guadalupe River and Coyote

Creek watersheds will follow a pattern related to the mercury concentration in these habitats, which, in turn, is reflective of these sites’ proximity to the New

Almaden Quicksilver Mine. Also, it is expected that the mercury levels found in the feathers will correlate with physiological and other biological measurements.

If these ideas are supported, it would suggest that these measurements, which are known proxies for the quality and condition of these birds, can potentially serve as bioindicators of contaminant exposure.

Many studies focus on the effect of mercury on aquatic organisms and their predators (J. A. Davis et al., 2012; Fallacara, Halbrook, & French, 2011;

Greenfield et al., 2013). Mercury can be altered into a bioavailable form through methylation. This commonly occurs in aquatic ecosystems. As such, aquatic organisms are highly susceptible to bioaccumulation and biomagnification of

mercury (Christopher H. Conaway, et al., 2008; Jackson et al., 2011). However, there are very few studies that examine mercury contamination in terrestrial organisms living in riparian habitats. This is certainly true for the Common

Yellowthroat (Robinson, et al., 2011), especially within the South Bay area.

Previous studies have focused on other species including waterbirds, shorebirds, and Song Sparrows. One finding was that songbirds living in terrestrial ecosystems adjacent to mercury contaminated watersheds had significant levels of mercury in their blood (Cristol et al., 2008). This discovery of mercury pollution in non-aquatic organisms and the fact that there is a dearth of studies on the issue demonstrate the need for further research on this subject. The proposed study is novel, because it includes an investigation of the effects of environmental mercury contamination in a species that is terrestrial and riparian, a subject not well studied in this area.

METHODS

Field site selection

Five field sites were chosen in the Santa Clara Valley along the Coyote

Creek, Guadalupe River, Los Alamitos Creek, Calero Creek, and Llagas Creek

(Fig. 6). Field sites at the Coyote Creek mouth and closer to the Coyote Creek source were designated Lower Coyote Creek and Upper Coyote Creek, respectively. Likewise, field sites at the Guadalupe River mouth and the

Guadalupe River source were designated Lower Guadalupe River and Upper

Guadalupe River. Los Alamitos Creek and Calero Creek are included in Upper

Guadalupe River. These streams were added to Upper Guadalupe River, because too few birds were found on the initial field location on Guadalupe

River (from Camden Avenue to Branham Lane in San Jose, CA). These sites were chosen with the aim of comparing data from birds caught close to the mouth of Coyote Creek to data from birds caught close to the source of Coyote

Creek (and closer to New Almaden Quicksilver Mine).

There was no historic mercury mining activity in the drainage region of

Los Gatos Creek; thus, this area was considered as a potential local reference field site (M. A. Thomas, et al., 2002). However, Llagas Creek was chosen as a reference field site for the following reasons: 1) Concentrations of mercury in

Llagas Creek near Gilroy, CA were an order of magnitude lower than in Los

Gatos Creek (M. A. Thomas, et al., 2002; Worcester, 1998). 2) No Common

Yellowthroats were found along Los Gatos Creek. 3) The field site on Llagas creek (in the Pajaro Watershed) is separated from the Guadalupe River and

Coyote Creek watersheds by the Llagas Creek and Uvas Creek watersheds.

Thus, it is unlikely that runoff from the Guadalupe River and Coyote Creek will affect mercury levels in Llagas Creek. 4) Llagas Creek may provide a more discrete comparison of mercury levels between streams in Santa Clara Valley and

Gilroy. Consequently, although Los Gatos Creek is within Santa Clara County,

Llagas Creek was chosen as the reference site

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orange diamond denotes New Almaden, CA denotes New Almaden, diamond orange

and the and

GoogleEarth, 2013 GoogleEarth,

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rea of field site, maroon circles denotes denotes cities, reacircles maroon field site, of

location of New Almaden Quicksilver Mine Mine Quicksilver location of New Almaden

Figure 6. Map of field sites in relation to one another and nearby cities. Legend: Areas outlined with yellow with yellow outlined andanother Areas Legend: in nearby cities. Figure one to field 6. relation sites Map of indicate a the

Sample collection

Common Yellowthroats were captured at the field sites between 11 May

2012 and 14 June 2012. This timeframe was chosen because it is the breeding season of Common Yellowthroats. The birds were the most territorial during this time and thus, most likely to respond to conspecific songs and calls

(Bousman, 2007; Shuford, 2008). The birds were lured into flying into a mist net using audio playbacks of conspecific songs and calls. The mist nets were observed some distance away once the playbacks were set at the net. Upon capture, birds were extracted immediately, and the amount of time from capture in the mist net to blood collection completion was recorded. Blood was collected via brachial venipuncture and the amount of blood collected was limited to ~1% of the bird’s body mass (50 µL to 100 µL) (Owen, 2011). Blood samples were kept on ice until further processing.

The following morphometric measurements were recorded: age, sex, weight, abdominal and furcular fat, cloacal protuberance score, brood patch score, left and right wing chord length, left and right tarsus length, keel length, molt, and primary and rectrice feather wear. Tarsus length, wing chord length, and keel length were measured with digital calipers (CS-200 Compact Scale,

OHAUS, NJ, USA) to the nearest 0.01 mm. Weight was measured using a digital scale (Model No. 147 – 6-inch digital fractional calipers, General Tools and

Instruments, NY, USA) to the nearest 0.1 g. FA was calculated as the absolute value of the difference between a left morphological feature and its corresponding right morphological feature (Eeva, et al., 2000). The outer two rectrices (tail feathers) were collected and placed in small envelopes until further analysis. Photos of the bib and mask (in profile) were taken for the male birds.

All measurements and blood samples were collected from adult birds only.

Animal handling protocols were approved by California State University

East Bay’s Institutional Animal Care and Use Committee on May 17, 2012.

Capture, banding, and sample collection from Common Yellowthroats were conducted under USGS permit number 22109.

Sample processing

Capillary tubes used to collect blood were spun at 12,000 g for six minutes in order to assess hematocrit level. Hematocrit level was determined using a hematocrit reader card (Critocaps™ Micro-Hematocrit Capillary Tube Reader,

Leica Microsystems, Germany). Plasma was extracted from the capillary tubes and stored at -20°C.

Blood smears were made using blood that was collected in less than three minutes to avoid the effect of stress hormones on increasing white blood cell counts (Grasman, 2002). Blood smears were Wright’s stained (Eosin-Wright’s dip stain, Medical Chemical Corporation, Torrence, CA, USA) for white blood cell

count assessment. White blood cells (leukocytes) were identified and counted in the blood slides, with focus on determining the heterophil-lymphocyte ratio.

Leukocyte types that were identified included lymphocytes, monocytes, thrombocytes, heterophils, eosinophils, and basophils (Campbell, 1995). Blood smears were scored using an Axiovert 100 light microscope (Zeiss, Germany).

Differential white blood cell numbers were quantified by counting the number of each type of white blood cells seen in a field view. This process was repeated for

100 field views. Heterophil-lymphocyte ratio was determined by continuously scanning the slide and counting 100 white blood cells of any type then calculating the ratio of heterophils to lymphocytes (Gross & Siegel, 1983).

Image analysis

Feather quality was assessed by determining distance between barbs and barbules density through examination using a USB microscope (Fig. 7). Photos of the feathers at 150x magnification were taken using the USB microscope.

These images were analyzed using Microviewer Software (EyeWitness Ltd.) and

GIMP 2.8.2 (GIMP Development Team, 2013). Distance between barbs was determined using the measurement capabilities in the Microviewer Software.

The distance between the two centermost barbs was measured along the rachis.

Barbule density was determined by counting barbules in a fixed area (0.15 mm2).

Photos of male Common Yellowthroat sexual characteristics were analyzed using GIMP 2.8.2 and ImageJ 1.47v (National Institute of Health, USA).

These characteristics include mask size, bib size, and bib color properties (hue, saturation, and brightness.) A portable photo box was used to maintain consistent lighting and a color plate (24ColorCard, Camera Trax) was included in each photo for post-processing. Color levels were adjusted using the white and grey color squares. Hue, saturation, and brightness values were recorded for the red, yellow, blue, and brown color squares. Hue values were within 18 units, while saturation and brightness values were within five units between each picture for a 95% match. (Image post-processing methods adapted from San

Francisco Bay Bird Observatory image analysis instructions).

Figure 7. Illustration of parts of a feather. The calamus is the hollow distal end of the rachis. The rachis is the central shaft and completely solid. Barbs extend from the rachis on each side of the feather. Barbules branch off of the barbs and interconnect with barbules on the adjacent barb using barbicels (or hooklets). Image adapted from (Podulka, Rohrbaugh, & Bonney, 2004).

Feather mercury analysis

Whole feathers were processed for total mercury. Prior studies have demonstrated that the more toxic form of mercury (methylmercury) has been found in proportions greater than 90% in bird blood and feathers. Thus, total mercury concentrations will serve as a proxy for methylmercury (J. Ackerman, et al., 2008; Robinson, et al., 2011).

The feathers were washed with high purity deionized water and dried at

35°C overnight. Total mercury analysis was conducted using Environmental

Protection Agency Method 7473 on a Milestone DMA-80 Direct Mercury

Analyzer (Milestone, Monroe, CT, USA) at the Moss Landing Marine

Laboratory’s Marine Pollution Studies Laboratory- Department of Fish and

Game. Quality assurance involved analysis of certified reference material (fish liver [DOLT-4] from the National Research Council of Canada, Ottawa, Canada) for each batch of analyses. Recoveries for the certified reference material averaged 102.8% (n=9). Relative percent difference was 0.19% for reference spikes and 2.70% for reference duplicates.

Morphometric and statistical analysis

Mintab 16.1.1 (Minitab Inc., USA) was used for statistical analyses.

Parametric tests were used, and normality was assumed because sample sizes were relatively small. Outliers were not removed for the same reason.

FA was calculated for wing chord length, tarsus length, rectrice weight and length, rectrice wear, barb distance, and barbule density. Effects of stream, stream location, and field site on the FA of these measurements were also investigated using one-way analysis of variance (ANOVA) tests.

Structural size of the bird was calculated using principal components analysis of three morphological characteristics (keel length, weight, and average tarsus length). Principal component one (PC1) was used as score of birds’ body size.

One-way ANOVA was used to investigate the effects of stream, stream location (upper, lower, or Llagas Creek), and field site on the following variables: weight, fat, cloacal protuberance or brood patch score, wing chord length, tarsus length, rectrice weight and length, keel length, primary and rectrice wear, hematocrit level, total white blood cell count, hematocrit-lymphocyte ratio, barb distance, barbule density, mask size, bib size, bib hue, bib color saturation, and bib color value, and rectrice mercury levels.

Significant differences between groups discovered using one-way

ANOVA were discriminated using Fisher’s LSD post hoc tests. Response variables that were determined to be statistically significant from one-way

ANOVA for both stream location and field site factors were further examined

with fully nested general linear model ANOVA. Significance of α = 0.05 was chosen for all tests, and values were reported as mean ± standard error (SE).

RESULTS

Primary and rectrice feather wear

Primary wear was significantly lower in birds caught at locations in lower area of streams ( x = 1.265 ± 0.172 , N = 17; one-way ANOVA, F = 5.526, p < 0.01;

Fig. 8). Rectrice wear was also significantly lower in birds caught in lower streams ( = 1.67647 ± 0.187, N = 17; one-way ANOVA, F = 2.086, p < 0.05; Fig. 8).

However, birds caught in upper streams did not have rectrice wear scores significantly different from birds caught in either lower streams or Llagas Creek

(Fig. 8).

Likewise, birds caught in Lower Coyote Creek and Lower Guadalupe

River also had lower primary wear scores compared to the other field sites

(Lower Coyote Creek: = 1.389 ± 0.261, N = 9. Lower Guadalupe River: = 1.125

± 0.227, N = 8; one-way ANOVA, F = 2.853, p < 0.05; Fig. 9). Rectrice wear was significantly different between Llagas Creek and Lower Coyote Creek only, where birds caught in Lower Coyote Creek had lower rectrice wear scores ( =

1.444 ± 0.176, N = 9; one-way ANOVA, F = 1.305, p = 0.062; Fig. 9).

Fluctuating asymmetry of barbule density

Barbule density FA in outer rectrices of birds caught in Llagas Creek were significantly lower ( = 0.1429 barbs ± 0.143 barbs, N = 7; one-way ANOVA, F =

3.059, p = 0.01; Fig.10) than the barbule density FA in outer rectrices of birds caught in other stream locations. This pattern is also reflected in field site, where birds in Llagas Creek also have the lowest barbule density FA in rectrices of all the field sites ( x = 0.1429 ± 0143 barbs, N = 7; one-way ANOVA, F = 1.640, p <

0.05; Fig. 10).

Bib area and bib hue

Bib area was significantly larger in birds caught in lower stream locations

( = 1289.8 mm2 ± 122 mm2, N = 8; one-way ANOVA, F = 503211, p < 0.01; Fig. 11) and at field sites in lower areas of Guadalupe River and Coyote Creek (i.e., the

Lower Guadalupe River ( = 1337.2 mm2 ± 195 mm2, N = 4; Fig. 11) and Lower

Coyote Creek field sites ( = 1242.4 mm2 ± 172 mm2, N = 4; one-way ANOVA, F =

2557736, p < 0.05; Fig. 11)). Similarly, bib hue was highest in birds caught in lower stream locations ( = 57.000 ± 0.378, N = 8; Fig. 12). Birds caught in upper stream locations did not significantly differ in bib hue from either lower stream locations or Llagas Creek, although bib hue was significantly different between birds in lower stream locations and Llagas Creek. (one-way ANOVA, F = 12.22, p

<0.05; Fig. 12). Llagas Creek birds exhibited the lowest bib hue of the three stream locations ( = 54.333 ± 0.615, N = 6; Fig. 12).

Bib hue was almost statistically different between field sites (one-way

ANOVA, F = 7.64; p=0.068). However post-hoc analysis demonstrated that

differences of bib hue between field sites mirrors the pattern seen in stream locations. Bib hue of birds caught in Lower Coyote Creek ( x = 57.250 ± 0.479, N =

4; Fig. 12) and Lower Guadalupe River ( = 56.750 ± 0.629, N = 4; Fig. 12) had the highest bib hue values. Birds caught at Llagas Creek had the lowest bib hue values ( = 54.333 ± 0.615, N = 6; Fig. 12).

extend to maximum and minimum and extend value. maximum to

rectrice wear score (right) for birds caught in lower or upper streams or at or in upper birdsor streams lower for at caught (right) score wear rectrice

Llagas Creek. Open circles indicate individual values. Closed circles indicate mean for each group. Horizontal Horizontal group.for indicate each mean indicate individual LlagasClosed values. circles Open circles Creek. Whiskers lower quartile. andlinesindicate upper median, quartile, from different letters significantly do are that share Groups not Method. Fisher Letters denote using grouping each other. (left) wearFigure 8. and Primary score

field site. field Open circles site.

Letters denote grouping Letters denote using

Method. Groups that do not share letters are significantly different from each other fromdifferent each are share not letters significantly do that Groups Method.

Figure 9. Primary wear score (left) and rectrice wear score (right) for birds caught in birds each for caught (right) score wear (left) wearFigure rectrice 9. and Primary score quartile, indicate upper indicate mean group.lines forHorizontal Closed indicate circles individual each values. maximum to and value. median,minimum extend lower quartile. Whiskers and Fisher

re significantly fromdifferent each reother. significantly

icate mean for each group. X symbols indicate outliers. Horizontal lines lines Horizontal outliers. indicate mean group.forX symbols icate each

Figure 10. FA of barbule density in rectrice feathers by stream location (left) and by field site (right). Open circles (right). Open circles field site by location by(left) in density feathers and barbule Figure rectrice stream 10. of FA ind Closed indicate circles individual values. Letters value. minimum and lower quartile. maximum indicateto median, extend Whiskers quartile, and upper letters doa that share not denote groupingGroups Method. Fisher using

te upper median, quartile, and te

individual values. Closed circles indicate mean for each group. Horizontal lines indica group.lines forHorizontal each indicate individual mean circles values. Closed Method. Fisher usingdenote grouping Letters andextend lower Whiskers value. maximum to minimum quartile. each do other. that share from Groups not different letters significantly are indicate Open circles (right). (left) stream locations field sites and birds different in of Figure caught 11. area Bib

imum value. Letters denote grouping using Fisher Method. Method. Fisher usingdenote grouping Letters imum value.

in different stream locations (left) and field sites (right). Open circles indicate indicate Open circles field sites (right). (left) stream locations different inand

Figure 12. Bib hue of Figure birds 12. hue of caught Bib indicate upper median, quartile, and group.lines forHorizontal each indicate individual mean circles values. Closed andextend lower Whiskers maximum to min quartile. each do other. that share from Groups not different letters significantly are

Structural size a,b Birds caught in areas of higher historical contamination had greater structural size. Indeed, the average structural size of the birds parallels the b historical mercury concentration gradient between the field sites. That is, largest structural size in Common Yellowthroats was found in birds caught at the Upper

Guadalupe River ( x = 28.041 ± 0.514, N = 3; Fig. 13) followed by those from the

Upper Coyote Creek ( = 27.398 ± 0.320, N = 6; Fig. 13). Birds with second to smallest average structural size were caught in Lower Guadalupe River ( =

27.47 ± 0.208, N = 8; Fig. 13), and the smallest birds on average were caught in

Lower Coyote Creek ( = 26.603 ± 0.258, N = 9; Fig. 13). Birds caught at the reference site, Llagas Creek, have structural sizes that fall between Upper Coyote

Creek and Lower Guadalupe River ( = 27.132 ± 0.312, N = 6; Fig. 13). However, structural size of the birds was not significantly different between field sites

(one-way ANOVA, F = 2.49, p = 0.67)

Total mercury in feathers

Total mercury levels in feathers were not significantly different between the three stream locations (one-way ANOVA, F = 47.3, p=0.080; Fig. 14). There were significant differences in total feather mercury between Upper Guadalupe

River and all other field sites. Birds in this field site contained the most total mercury in their rectrice feathers ( = 10.124 µg/g ± 0.100, N = 4; one-way

ANOVA, F = 55.5, p<0.05; Fig. 14). Additionally, after nested general linear model ANOVA, total feather mercury was significantly different between field sites within stream locations (F = 4.51, p < 0.05) but not between stream locations

(F = 0.97, p = 0.510). That is upper streams, lower streams, and Llagas Creek birds significantly differed in total feather mercury but Upper Guadalupe River and

Upper Coyote Creek birds (for example) did not significantly differ.

All other variables were found to be not significantly different between stream locations or field sites. Also, stream did not have significant interaction with any of the measured variables.

en circles indicate en indicate circles

different from each other. from different

ed circles indicate mean for each group. Horizontal lines indicate indicate upper median, quartile, and group.lines forHorizontal each indicate mean circles ed

individual values. individual values. Clos Method. Fisher usingdenote grouping Letters andextend lower Whiskers value. maximum to minimum quartile. do that share Groups not letters significantly are Op (right). (left) locations field differentsites in and birds stream Figure of 13. caught size Structural

. Horizontal lines lines Horizontal .

Figure 14. Total Hg in feathers of birds caught in different stream locations (left) and field sites (right). (right). Open (left) circles locations differentfield sites inand caught birds feathers Figure stream in Hg 14. of Total outliers indicate indicate mean group.forX symbols Closed indicate circles individual each values. Letters value. minimum and lower quartile. maximum indicateto median, extend Whiskers quartile, and upper from different letters each doare other. that share not significantly denote groupingGroups Method. Fisher using

DISCUSSION

Primary and rectrice feather wear

Common Yellowthroats exhibited significant differences in primary and rectrice feather wear, FA of barbule density, bib area and bib hue, and structural size between field sites and between stream locations. Total mercury contamination increases in proximity to the New Almaden Mining District.

These areas included upper stream locations and Lower Coyote Creek and

Lower Guadalupe River. Of the streams in Santa Clara Valley, CA, Guadalupe

River had the highest levels of mercury (M. A. Thomas, et al., 2002; Worcester,

1998). Birds caught in Lower Guadalupe River and Lower Coyote Creek are potentially exposed to relatively high amounts of environmental MeHg compared to other areas in Santa Clara Valley. Thus, birds in these areas are expected to show effects of mercury exposure that decrease reproductive and/or survival fitness (J. Ackerman, et al., 2008; J. T. Ackerman, et al., 2008; Joshua T.

Ackerman, et al., 2012; T. Dauwe, et al., 2006; Jay A. Davis, et al., 2003; Sillanpaa, et al., 2010).

Increased primary and rectrice wear in birds located in upper stream areas and Upper Coyote Creek and Guadalupe River could be a result of stressors caused by environmental perturbations. Increased levels of corticosterone (a

glucosteroid hormone released in response to physiological stressors) during molt may result in re-grown feathers that are of poor quality. European Starlings

(Sturnus vulgaris) with elevated corticosterone due to food-restriction had lower barbule density and lower tensile strength than a non-stressed control group

(Bortolotti, Dawson, & Murza, 2002; DesRochers et al., 2009). The birds caught in

Upper Coyote Creek and Guadalupe River may have had higher circulating levels of MeHg during the beginning of molt and deposited MeHg in the most proximal ends of their primaries and rectrices which concurs with previous findings that heavy metals tend to be found in larger concentrations at the proximal end of feathers (Bortolotti, 2010). Moreover, birds caught in Upper

Guadalupe River may have had higher MeHg levels compared to birds caught in

Upper Coyote Creek, because the average rectrice and primary wear is lower in birds caught in Upper Coyote Creek. The structurally compromised proximal tips of the feathers would have worn away. This could also account for the lack of significant difference in total feather mercury between field sites (except in

Upper Guadalupe River).

Fluctuating asymmetry of barbule density

Birds caught in watersheds in Santa Clara Valley (which have higher historical mercury contamination) had greater barbule density asymmetry compared to birds caught in the Pajaro watershed near Gilroy. Variations in

barbule density can create a cycle in which barbule density and foraging capabilities influence each other.

European Starlings with increased barbule density also show decreased barbicels hooking strength in their feathers, reducing the ability of the feather to remain intact during flight (DesRochers, et al., 2009). Furthermore, barbule density is affected by increased corticosterone due to stressors, such as infection, food restriction, or psychological stress (DesRochers, et al., 2009; Pap, Vagasi,

Barbos, & Marton, 2013). Effects of MeHg ingestion include decreased foraging efficiency and food seeking behavior (Joshua T. Ackerman, et al., 2012).

Therefore, Common Yellowthroats in Santa Clara Valley may experience more acute effects on food seeking behavior in areas of high historical of environmental MeHg than birds caught in Llagas Creek during their molt .

Consequently, the birds may express these effects through barbule density.

The asymmetry of barbule density found in Santa Clara Valley Common

Yellowthroats expose them to further behavioral vulnerabilities that impact survival fitness vis a vis flight performance. Since higher barbule density could result in decreased barbicels hooking strength, feathers with higher barbule density are more prone to wear (Pap, et al., 2013). Uneven wear between left and right primary or rectrice feathers diminishes turning maneuverability (Swaddle,

Witter, Cuthill, Budden, & McCowen, 1996; A. L. R. Thomas, 1993).

Asymmetries in birds’ tails can also alter required power produced by the wings for forward movement and reduce the amount of lift and steering capabilities provided by the tail (A. L. R. Thomas, 1993). Poor maneuverability is especially detrimental to insectivorous birds (like Common Yellowthroats) that rely on precise flight maneuvers to capture prey (Park, Hino, & Ito, 2008; Sillanpaa, et al.,

2010). Birds with compromised aerodynamics may also have to make physiological adjustments in order to escape predators. Migrating birds can adjust their total body mass (typically by reducing body mass) and increase pectoral muscle size to increase wing loading and power produced by the wings.

However, these adjustments may have associated costs as reduction in body mass increases starvation susceptibility (van den Hout, Mathot, Maas, &

Piersma, 2010)

Bib area and bib hue

Birds caught in areas with higher mercury (i.e., upper stream locations) had lower quality plumage sexual signals. Bibs of the male Common

Yellowthroats had smaller area and lower hue values in Upper Guadalupe River and Upper Coyote Creek. Hue is a parameter associated with feather carotenoid coloration (Tom Dauwe & Eens, 2008). Birds living in areas with historically higher mercury levels may use carotenoids to combat oxidative stress induced by environmental mercury exposure, thereby reducing the amount of carotenoids

allocated for feather coloration (Tom Dauwe & Eens, 2008; Geens, et al., 2009).

However, the antioxidant properties of carotenoids in vivo have been debated.

Great Tits subjected to oxidative stress and/or given a carotenoid supplemented diet did not exhibit significantly different circulating levels of carotenoids or different carotenoid coloration compared to control groups. (Isaksson &

Andersson, 2008). Nevertheless, bib size has been related to female mate choice, with preference toward larger bibs (Freeman-Gallant, et al., 2010). Common

Yellowthroats with lower bib hue and smaller bibs (those found in Upper stream locations) could be affected both in present fitness and future reproduction.

Structural size

The pattern of structural size of the birds compared with location does not appear to fit the prediction that body condition (since structural size can be used as an index of body condition) decreases with increasing proximity to a mercury source or historical environmental contamination (Joshua T. Ackerman, et al.,

2012; T. Dauwe, et al., 2006). Though birds in captive studies show reduced foraging motivation and efficiency, it is possible that the only Common

Yellowthroats that were able to thrive in these high historically contaminated areas were individuals that had greater foraging effectiveness that results in greater structural size in birds caught in areas with high levels of mercury contamination (Joshua T. Ackerman, et al., 2012). It is possible that birds heavily

affected by environmental mercury contamination in Upper Guadalupe River and Upper Coyote Creek were not able to survive or moved to areas that posed less danger of MeHg contamination. Goosanders (Mergus merganser) with “very good” body condition, calculated from a ratio of body mass to body length and a ratio of body length to keel length, were presumed to be more successful, efficient foragers and were also found to have higher levels of total mercury, indicative of a higher bioaccumulation of mercury than Goosanders that were poor foragers with poor body condition (Kalisinska, Budis, Podlasinska,

Lanocha, & Kavetska, 2010).

In addition, the structural size and location pattern may be confounded by sex differences. Dauwe et al. (2006) found that female Great Tits had lower body mass compared to males in the same location. This was a result of male Great

Tits outcompeting female Great Tits (who are subdominant to males) for food (T.

Dauwe, et al., 2006). This difference between sexes may not have been revealed in this study, because the numbers of female Common Yellowthroats caught for this experiment were too small.

CONCLUSION

This investigation on environmental mercury contamination on the body condition and quality of Common Yellowthroats has provided new insights into the effect of mercury on a species and ecosystem not previously examined. The results of this study show that there is a statistically significant and potentially adverse relationship between environmental mercury contamination and flight feather quality, feather structural symmetry, and sexual signals in Common

Yellowthroats.

Environmental mercury contamination first became a concern with the emergence of Minamata Disease. Realization that anthropogenic sources of mercury from industrial processes could create a public health and environmental health problem has greatly reduced emissions of mercury into the environment beginning in the 1970s. However, the legacy of environmental mercury contamination cannot be so easily mitigated. Anthropogenic mercury emissions have increased the flux of mercury in its biogeochemical cycle. As a result, mercury can more readily transform into the highly toxic and bioavailable form, MeHg.

Because the methylation of MeHg primarily occurs in aquatic systems via sulfate-reducing bacteria, a significant amount of research has been conducted on

marine and freshwater ecosystems and species. However, streams in watersheds within Santa Clara Valley, CA have some of the highest levels of mercury in the

United States. In addition, there are many geographical features (high urbanization, location of marshes and reservoirs) that increase the likelihood of

Hg (II) methylation into MeHg. Therefore, there is potential for environmental mercury to adversely impact the riparian ecosystems of Santa Clara Valley.

Because Common Yellowthroats are insectivorous, they can bioaccumulate MeHg. Although total mercury levels were not significantly different between birds caught in different areas of historical mercury contamination, the birds did exhibit effects that could reduce reproductive and survival fitness. That is, sexual signals of Common Yellowthroats in areas with historically high mercury contamination were smaller and had lower hue values.

Also, feather quality was compromised, which may affect foraging ability of the birds.

Future research could include sampling the same population over a number of years and involve date of capture as an additional factor in statistical analyses. Additionally, multiple sampling years could improve robustness of statistical models. Nest monitoring could be added in order to measure direct affects of historical mercury contamination on reproductive success. Observing the average fledgling success would indicate whether the less attractive sexual

signals of male Common Yellowthroats in field sites with high mercury actually do have an effect on reproductive success.

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APPENDIX

A-1. Rotary furnace used for mercury ore processing in New Almaden Quicksilver County Park in south San Jose, CA. Photo by Deanna de Castro

A-2. Male common yellowthroat caught in mist net. Photo by Deanna de Castro

A-3. Male Common Yellowthroat. Photo by Deanna de Castro

A-4. Collecting blood samples and morphometric measurements from a Common Yellowthroat. Photo by Josh Scullen