Prepared in cooperation with the South Bay Salt Pond Restoration Project

Effects of Human Disturbance on Waterbird Nesting Effort 

and Reproductive Success at Restoration Pond SF2, 

South San Francisco Bay, California

U.S. Department of the Interior

U.S. Geological Survey

Open-File Report 2014–1223
Cover: Aerial photograph of Pond SF2 after construction of bird nesting islands. Image from Google Earth®, 2014.
Effects of Human Disturbance on Waterbird Nesting and 

Reproductive Success at Restoration Pond SF2, South 

San Francisco Bay, California

By Joshua T. Ackerman, Mark P. Herzog, and C. Alex Hartman

Prepared in cooperation with the South Bay Salt Pond Restoration Project

Open-File Report 2014-1223

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2014 

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Suggested citation:

Ackerman, J.T., Herzog, M.P., and Hartman, C.A., 2014, Effects of human disturbance on waterbird nesting and 

reproductive success at restoration pond SF2, south San Francisco Bay, California: U.S. Geological Survey OpenFile Report 2014-1223, 16 p, http://dx.doi.org/10.3133/ofr20141223. 

ISSN 2331-1258(online)
iii

Contents

Abstract ...................................................................................................................................................................... 1

Introduction................................................................................................................................................................. 2

Study Objectives ..................................................................................................................................................... 2

Study Area .............................................................................................................................................................. 2

Methods...................................................................................................................................................................... 3

Nest Monitoring....................................................................................................................................................... 3

Estimation of Breeding Parameters......................................................................................................................... 3

Statistical Approach ................................................................................................................................................ 3

Variable Importance ............................................................................................................................................ 4

Results and Discussion .............................................................................................................................................. 4

Nesting Performance of Waterbirds at Restoration Pond SF2 in 2011 and 2012.................................................... 4

Spatial Distribution of Nests Relative to Potential Disturbance Features ................................................................ 5

Disturbance Effects on Breeding Waterbirds........................................................................................................... 5

Nest Success Relative to Distance from Potential Disturbance Features............................................................ 5

Effects of Disturbance Features on Nest Survival ............................................................................................... 5

Effects of Disturbance Features on Nest Initiation Date and Clutch Size ............................................................ 6

Summary .................................................................................................................................................................... 7

Acknowledgments....................................................................................................................................................... 7

References Cited........................................................................................................................................................ 8

Figures

Figure 1. Location and final nest fate of American Avocet (Recurvirostra americana) nests at restored Pond SF2, 

south San Francisco Bay, California, 2011–12.......................................................................................................... 9

Figure 2. American Avocet (Recurvirostra americana) daily nest survival (A) and nest success (B) were lower in 

nests located farther from the highway (State Route 84), South San Francisco Bay, California.............................. 10

Tables

Table 1. Spatial distribution and final nest fate of American Avocet (Recurvirostra americana) nests relative to 

potential disturbance features at restored Pond SF2, south San Francisco Bay, California, 2011–12. ................... 11

Table 2. Model selection results for effects of potential disturbance features on daily nest survival of American 

Avocets (Recurvirostra americana) at restored Pond SF2, south San Francisco Bay, California, 2011–12. ........... 12

Table 3. Relative variable importance metrics for effects of potential disturbance features on daily nest 

survival of American Avocets (Recurvirostra americana) at restored Pond SF2, south San Francisco Bay, 

California, 2011–12.................................................................................................................................................. 13

Table 4. Model selection results for effects of potential disturbance features on clutch size of American 

Avocets (Recurvirostra americana) at restored Pond SF2, south San Francisco Bay, California, 2011–12. ........... 14

Table 5. Relative variable importance metrics for effects of potential disturbance features on clutch size of 

American Avocets (Recurvirostra americana) at restored Pond SF2, south San Francisco Bay, California,

2011–12................................................................................................................................................................... 15

Table 6. Model selection results for the effects of potential disturbance features on nest initiation date of 

American Avocets (Recurvirostra americana) at restored Pond SF2, south San Francisco Bay, California, 

2011–12................................................................................................................................................................... 15

Table 7. Relative variable importance metrics for effects of potential disturbance features on nest initiation 

date of American Avocets (Recurvirostra americana) at restored Pond SF2, south San Francisco Bay, 

California, 2011–12.................................................................................................................................................. 16
iv

Conversion Factors, and Abbreviations and Acronyms

Conversion Factors

Inch/Pound to SI 

Multiply By To obtain

Length

foot (ft) 0.3048 meter (m)

SI to Inch/Pound

Multiply By To obtain

Length

meter (m) 3.281 foot (ft) 

meter (m) 1.094 yard (yd) 

Area

square meter (m2) 0.0002471 acre 

square meter (m2) 10.76 square foot (ft2) 

hectare (ha) 2.471 acre

hectare (ha) 0.003861 square mile (mi2) 

Abbreviations and Acronyms

AIC Akaike’s Information Criterion

CI confidence interval

R2 coefficient of determination

SBSP South Bay Salt Pond

VI variable importance
1 

Effects of Human Disturbance on Waterbird Nesting and 

Reproductive Success at Restoration Pond SF2, South 

San Francisco Bay, California

By Joshua T. Ackerman, Mark P. Herzog, and C. Alex Hartman

Abstract To offset for the loss of managed pond habitat during restoration of wetlands to tidal marsh, the 

South Bay Salt Pond (SBSP) Restoration Project is enhancing some of the remaining ponds by 

constructing islands for roosting and nesting waterbirds. Among these wetland habitats, the SBSP 

Restoration Project also is installing walking trails and viewing platforms in an effort to bring the public 

closer to nature. In winter of 2010–11, the SBSP Restoration Project constructed 30 islands in Pond SF2 

and walking trails and viewing platforms around the edge of the pond. The restoration project partners 

acknowledged that human disturbance could detrimentally affect nesting and roosting waterbirds. 

Although optimal buffer distances and potential for human disturbance were unknown, islands in Pond 

SF2, nevertheless, were designed with built-in buffers of greater than 300 feet (91 meters) from a trail 

and 600 feet (182 meters) from a viewing platform in order to minimize potential human disturbances. 

To determine the effects that human disturbance may have on waterbirds nesting on these newly 

constructed islands in Pond SF2, we assessed the potential effects of human disturbance features 

(specifically, access trails, viewing platforms, internal pond berms, exterior levees, and highways) on

breeding waterbirds in 2011 and 2012. We found no clear pattern of potential disturbance features on a 

group of reproductive factors, including nest survival, nest initiation date, and clutch size. Because all 

the islands were constructed greater than 90 meters from the nearest disturbance feature, Pond SF2 

alone did not provide adequate variation in the distance of disturbance features to detect potential 

detrimental effects for islands closer to disturbance features in other areas of the SBSP Restoration 

Project. If there is a need for SBSP Restoration Project Management Team to understand how close 

islands can be built to disturbance features in the future, we suggest a more comprehensive study that 

includes multiple ponds, other than SF2, with islands at varying distances to disturbance features.
2 

Introduction

San Francisco Bay is the largest estuary on the West Coast of North America, but nearly all tidal 

marshes and tidal flats have been destroyed due to urban development, agriculture, and salt production 

(Goals Project, 1999). In an effort to restore tidal habitat in South San Francisco Bay, the South Bay 

Salt Pond (SBSP) Restoration Project is implementing a plan to convert 50–90 percent of these former 

salt ponds into tidal and managed marsh habitats within the next 50 years (Goals Project, 1999; Steere 

and Schaefer, 2001; Siegel and Bachand, 2002; Life Science!, 2003). 

The San Francisco Bay annually supports more than 1 million waterbirds and is a RAMSARdesignated site of hemispheric importance for the conservation of shorebirds (Page and others, 1999; 

Morrison, 2001; Stenzel and others, 2002). Shorebird abundances during peak spring migration have 

exceeded 200,000 shorebirds in a single salt pond (Stenzel and Page, 1988). Although the restoration of 

former salt ponds to tidal marsh will increase habitat for many animals, it also will reduce the overall 

availability of pond habitats for wintering, migratory, and breeding waterbirds. A goal of the SBSP 

Restoration Project is to maintain current waterbird populations. Toward this goal, the first phase of the 

SBSP Restoration Project is to reconfigure and enhance two existing ponds (Ponds A16 and SF2) by 

constructing islands to increase roosting and foraging opportunities and to provide waterbird nesting 

habitat (Trulio and others, 2007). The number of waterbirds breeding within Pond SF2 (especially 

American Avocets [Recurvirostra americana], Black-necked Stilts [Himantopus mexicanus], and 

Forster’s Terns [Sterna forsteri]) are expected to increase with the additional nesting islands, but 

increased public access and associated human disturbance may potentially detrimentally affect

reproductive success. (These birds are referred to hereafter as “Avocets,” “Stilts,” and “Terns,” 

respectively.) For example, birds may flush and leave nests unprotected from predators in response to 

public activity occurring in close proximity to nesting sites. In addition to the potential overt effect of 

disturbance on nest mortality, disturbance also may affect overall reproductive output. Immediate 

disturbance may cause a pair to abandon their clutch or to lay fewer eggs. Birds avoiding disturbance 

also may select less-optimal nesting sites that may be more vulnerable to predation. Thus, in addition to 

the potential effect of disturbance on nest survival, clutch size and placement of nest sites also might be 

affected by disturbance. At the request of the SBSP Restoration Project Team, we were asked to 

examine the effect of disturbance features within Pond SF2 on waterbird reproductive success during 

the 2011 and 2012 breeding seasons. Disturbance features examined included internal berms, and 

proximities to Highway 84 (State Route 84), a perimeter levee, viewing platforms (placed at least 182 m 

from constructed islands), or walking trails (placed at least 91 m from constructed islands). 

Study Objectives

The goals of this study were: 

1. To estimate nesting performance (nest survival, clutch size, and nest initiation date) of 

nesting waterbird species (Avocets, Stilts, or Terns) within the outer two cells of Pond SF2 

that were enhanced with 30 nesting islands. 

2. To quantify the effects that the proximity of disturbance features (specifically, access trails, 

viewing platforms, internal pond berms, exterior levees, and highways) has on reproductive 

success.

Study Area

The study area for this supplemental proposal was enhanced Pond SF2, located within the 

Ravenswood complex of historical salt ponds (fig. 1).
3 

Methods

Nest Monitoring

Throughout the nesting season (April–August 2011 and 2012), all 30 islands in Pond SF2 were 

visited weekly to monitor waterbird nesting activity. We uniquely marked each newly initiated nest, and 

recorded Universal Transverse Mercator (UTM) coordinates of each nest (Garmin® GPSMAP 76, 

Garmin International Inc., Olathe, Kansas). At each weekly nest visit, we floated eggs to determine 

embryo age (Ackerman and Eagles-Smith, 2010), recorded clutch size, determined overall nest fate 

(hatched, failed, abandoned, or depredated), and determined the fate of each individual egg (hatched, 

failed-to-hatch, abandoned, or depredated). 

Estimation of Breeding Parameters

Daily nest survival rates were estimated based on weekly nest visits using logistic exposure 

models (Shaffer, 2004). A nest was considered to have survived an interval if the clutch was still 

completely or partially intact, embryo development had progressed, and there were no signs of nest 

abandonment (such as cold eggs). A nest was considered successful if 1 or more eggs successfully 

hatched. A nest was considered unsuccessful if it was depredated or abandoned. Exposure days were 

calculated as the number of days between nest visits, except when a final nest fate occurred between 

visits (hatched, depredated, or abandoned). For hatched nests, exposure days were calculated for the 

final interval based on the expected hatch date (Ackerman and Eagles-Smith, 2010). For depredated 

nests, exposure days were calculated for the final interval as the mid-point between nest visits. For 

abandoned nests, exposure days for the final interval were calculated as the difference between the 

developmental age of the eggs when the nest was abandoned (estimated by egg flotation) and the 

developmental age of the eggs when the nest was last visited. We censored nests that were abandoned 

because of investigator disturbance (such as egg collections). Nest success was calculated as the model 

averaged product of daily nest survival over the 27-day egg-laying and incubation period (Ackerman 

and others, 2013). 

Clutch size was estimated as the total number of eggs laid per female in a single nest. To reduce 

error associated with partial clutch depredation, we limited the estimation of clutch size to only nests we 

initially detected during laying or within 8 days of the onset of incubation. 

Nest initiation date was defined as the date on which the first egg of the nest was laid. For nests 

detected during egg-laying, we assumed one egg was laid per day and, thus, nest initiation date was 

estimated as the date the nest was detected minus the number of eggs in the nest when detected. For 

nests detected after incubation had started, we assumed incubation began when the last egg was laid, 

and nest initiation date was estimated as the date the nest was detected minus the average age of eggs (in 

days) and the number of eggs in the nest.

Statistical Approach

All statistical analyses were done using R 3.1.1 (R Core Team, 2014). All modeling was done 

using an information-theoretic approach (Burnham and Anderson, 2002). Nest survival models (as 

described in section, “Estimation of Breeding Parameters”) used the logistic exposure method (Shaffer,

2004). Standard linear models were used to examine the effects of disturbance features on clutch size 

and nest initiation date. Predictions and covariate slope estimates were model-averaged estimates over 

the full suite of a priori models. 
4 

Variable Importance

We developed an additional metric, variable importance (VI), in order to provide a more usable 

measure of the importance of a given variable within a suite of models by comparing the difference in 

final (or posterior) parameter weight with its initial (or prior) weighting. Prior weighting represents the 

expected parameter likelihood if all models are equally weighted. This is simply represented as the 

proportion of models within the full a priori model set in which a given variable is present. The 

posterior model weighting is defined as the parameter likelihood, or the sum of the model Akaike’s 

Information Criterion (AICc) weights for the set of models when the given variable was present

(Burnham and Anderson, 2002). Variable importance was defined as the log-odds ratio of the posterior 

and prior variable weights, and was described as follows:

P0 = PPPPP VV VVVV W Wht

 P = PPP PPPP VV VVVV W Wht ( p p l h o)

VV VVVV I II (V ) = log �

� P

1 − P�

� P0

1 − P0

�

�

 = log � P

1 − P� − log � P01 − P0

�

 = (P) − (P0)

Similar to the standard parameter likelihood, the variable importance metric, VI, provides a 

relative measure of how much a given variable is supported by the data and is calculated by summing all 

the model weights where the variable was present and comparing this value to the parameter likelihood 

of the other variables. However, VI also attempts to correct for the potential bias that may exist when the 

a priori model set is unbalanced and some variables are included in more models than others (that is, 

when the prior variable weights (P0) are not the same for all variables). 

Results and Discussion

Nesting Performance of Waterbirds at Restoration Pond SF2 in 2011 and 2012

We located a total of 170 Avocet nests (166 nests in 2011; 4 nests in 2012) at Pond SF2 (table 1; 

fig. 1). Although Stilts nested in small numbers within the salt pan of Pond SF2 (cell 3), Stilt nests were 

not observed within the regions of the pond that were enhanced with nesting islands. Terns did not nest 

at Pond SF2 in 2011 or 2012. Hereafter, all nesting statistics are for Avocets. 

In 2011, the average nest initiation date for Avocets at Pond SF2 was May 7, and average clutch 

size was 3.77 ± 0.06 eggs. These results are comparable to the long-term records for nest initiation dates 

and clutch sizes (Ackerman and Herzog, 2012; Ackerman and others, 2013). In 2012, the nest initiation 

date was similar (May 5); however, clutch size was significantly less (2.92 ± 0.18), but most likely 

represents the small sample size of only 4 nests. 

The percentage of nests that were successful was 64 percent (109 of 170 nests); all successful 

nests occurred in 2011, and the 4 nests observed in 2012 failed (table 1). Partial depredation (the loss of 

1 or more eggs without the full nest being depredated) occurred on 42 (38.5 percent) of the successful 

nests. A total of 50 nests (29.4 percent) were destroyed by predators, and 6.5 percent of nests were 

abandoned. Overall nest success in 2011 for Avocets at Pond SF2 was 57.8 percent (95-percent 

confidence interval [CI]=43.1–69.4 percent; N=166), based on a simple logistic exposure model of daily 

survival, with age of nest as the only covariate and a 27 day incubation period). 
5 

Spatial Distribution of Nests Relative to Potential Disturbance Features

Given the small sample of nests observed at Pond SF2 in 2012, there was no statistical power to 

detect differences in spatial distribution between years, and all summary statistics and analyses 

presented are with all years combined. In 2011 and 2012, Avocets nested an average of 142 ±7 m from 

berms, 329 ±9 m from the highway, 188 ±5 m from levees, 315 ±9 m from viewing platforms, and 221 

±6 m from publically accessible trails. For each island, we overlaid a grid with 1-m spacing, and 

measured the distance of disturbance features to the centroid of each 1-m2 pixel using the Spatial 

Analyst extension 10.2 for ArcMapTM 10.2 (Environmental Research Systems Institute, Inc., Redlands, 

California). Island polygons were digitized from 2010 high-resolution imagery acquired by the San 

Francisco Bay Estuary Field Station of the U.S. Geological Survey Western Ecological Research 

Center. Distance values then were averaged over all pixels to provide average distances to each 

disturbance feature (table 1). Using individual nest Global Positioning System coordinates, we 

identified which 1-m2 pixels on each island were used or not used for nesting. Based on Welch’s twosample t-test, and assuming all locations on all islands were suitable for nesting, Avocets nested 16 m 

farther from trails (95-percent CI=6–25; t=-3.21; df=170.36; p=0.002), and 33 m closer to viewing 

platforms (95-percent CI=17–51; t=3.94; df=170.15; p=0.0001) than would be expected by chance. We 

did not detect any differences among unused locations and actual nest locations for distance to highway

(t = 0.40; df=170.28; p=0.69), distance to trail (t= 1.607; df=170.38; p=0.11), or distance to internal 

berms (t=-1.34; df=170.15; p=0.18).

Disturbance Effects on Breeding Waterbirds

Nest Success Relative to Distance from Potential Disturbance Features

There were no differences in the location of successful nests and unsuccessful nests with respect 

to their distance from highways (t=1.64; df=111.61; p=0.10), internal berms (t=0.08; df=110.41; 

p=0.94), levees (t= -0.43; df=132.75; p=0.67), viewing platforms (t=1.39; df=117.44; p=0.17), or trails

(t=1.22; df=114.88; p=0.23). 

Effects of Disturbance Features on Nest Survival

We required nest age to be in all models, and daily nest survival was negatively related to nest

initiation date (tables 2 and 3). Variable importance (VI) was extremely high (17.76) for nest initiation 

date, indicating strong support for inclusion of this variable. In fact, cumulative model weight for 

models that included both nest age and initiation date exceeded 0.99, which suggests that a model with 

these two variables is 1.5 × 107 times more likely to represent the processes within the observed data 

than any of the a priori models that did not include them. Although a model that included a quadratic 

relationship with nest age performed nearly as well as the model with a linear relationship 

(ΔAICc=0.24), variable importance for the quadratic term was negative, indicating that this variable was 

not supported. We, therefore, interpreted the potential effects of disturbance features in relation to a base 

model of nest age and nest initiation date because these variables were so important for estimating 

Avocet nest survival. 
6 

In accordance with the general patterns observed in nest success of Avocets at Pond SF2 (table 

1), the models of daily nest survival provide some support for an increase in daily nest survival for 

Avocets that nest closer to the highway (table 2). Additionally, VI was 1.94, indicating that these data 

support the inclusion of this variable in models of daily survival rate. However, the 95-percent CI of the 

model-averaged covariate (β=-0.003–0.001) associated with the distance of nest from highway includes 

zero, which indicates there also is uncertainty regarding the magnitude of this effect. Model-averaged 

estimates of daily survival rate decreased linearly over the observed range of distances that nests were 

found from the highway, indicating that daily survival rate was lower for nests observed farther from the 

highway (fig. 2A). Avocet nests are typically incubated for 27 days (Ackerman and others, 2013), 

resulting in model-average nest success estimates that vary from 56.7 percent for nests farthest away 

from the highway (566 m; 95-percent CI=23.3–79.3 percent) to 73.1 percent for those nests closest to 

the highway (138 m; 95-percent CI=46.5–87.5 percent; fig. 2B). 

All other disturbance variables included in the a priori candidate model set were not supported 

by these data (tables 2 and 3). Variable importance for all other variables was negative (indicating a lack 

of support; table 3) and model weight was at most 0.04 (and usually much lower), indicating that the top 

model was at least 6.99 times more likely than any other model that included distance from a potential 

disturbance feature (table 2). 

Effects of Disturbance Features on Nest Initiation Date and Clutch Size

Clutch size decreased in later initiated nests (βinitdate=-0.011 ±0.003; tables 4 and 5). The only 

disturbance feature that may have influenced clutch size in these data was the distance to levee, but the 

data only provide weak support for this hypothesis. Avocets that nested farther from the Pond SF2 

levees appeared to have higher clutch sizes, because the model with distance to the nearest levee was 

1.89 times more likely than the same model without it included (table 4). The top model explained only 

13 percent of the total variation (R2=0.13) and the model-average slope for the distance to levee 

covariate showed substantial variation, with 95-percent CI including the possibility of no effect (95-

percent CI for βlevee= -0.0001–0.004; table 5). Although these data support the hypothesis that the clutch 

size of Avocet nests increases for nests farther from the levee, it is difficult to infer that activities of 

disturbance on the levee are the cause for this decrease. Instead, this relationship may indicate that highquality sites are farther from the levee and are selected earlier by high-quality pairs, and high-quality 

pairs have, on average, a larger clutch. Regardless of the potential cause, the overall effect on clutch size 

was relatively minor and overlapped the possibility of no effect. 

Initiation date of Avocet nests increased with the distance the nest was located from a viewing 

platform (table 6). In fact, this relationship was by far the most supported hypothesis among the a priori

candidate model set and was 121 times more likely than any other model. Model-averaged estimates 

suggest that initiation date increased as much as 6 days for every 100 m farther from a viewing platform 

the nest was located (βplatform=0.060 ±0.017; table 7). However, overall model performance was poor 

(R2=0.06) and distance from disturbance features explained little of the overall variation observed in 

Avocet nest initiation date. Similar to our conclusion with clutch size, we believe this pattern of 

increasing nest initiation date farther from viewing platforms may indicate settling patterns unrelated to 

the actual disturbance features. Regardless, given that nests closer to the viewing platform are initiated 

earlier, there does not appear to be any detrimental effects caused directly by human disturbance 

associated with the viewing platform at the distances observed. 
7 

Summary 

Although various factors generally influence specific reproductive or nesting characteristics, 

there was no consistent pattern that showed any linkages between negative breeding performance and 

potential disturbance features. Instead, several positive relationships with potential disturbance features

were documented, including earlier nesting dates the closer the nest was located to a viewing platform, 

larger clutch sizes for nests located closer to a pond levee, and increased nest success the closer the nest 

was located to the highway. Whether these relationships reflect causal relationships is unknown, but 

there were no observable detrimental effects on waterbird reproductive performance caused by these 

potential disturbance features. 

However, most of the public viewing features had minimal visitation by humans, and, therefore 

minimal disturbance levels during the 2011 and 2012 breeding seasons, relative to other ponds that

received higher use by the public. Pond SF2 also lacked the necessary islands close enough in proximity 

to potential disturbance features to detect effects of human disturbance on nesting waterbirds. 

Specifically, all islands in Pond SF2 were located more than 90 meters from public access trails and 

more than 180 meters from public viewing platforms. Therefore, we were not able to estimate the 

expected effects of public-access features on the reproductive success of waterbirds across the range of 

distances that already occur throughout the SBSP Restoration Project area. If the ultimate goal is to 

understand the buffer distance necessary to avoid disturbance effects on breeding waterbirds, then a 

larger study (involving multiple ponds with islands at varying distances to potential disturbance 

features) is necessary. A management tool could be generated from such a study to estimate the 

appropriate buffer distance for placement of future constructed islands, and the placement of walking 

trails and viewing platforms at ponds that already have existing nesting island habitat. 

Given these data limited to only Pond SF2, we would not expect detrimental effects on birds 

nesting on islands located more than 90 meters away from potential disturbance features. However, we 

cannot provide any assessment about how much closer to disturbance features islands could be built and 

still not influence breeding performance without a larger study including more ponds and more islands 

at varying distances from potential disturbance features. 

Acknowledgments This study was funded by the Resources Legacy Fund and South Bay Salt Pond Restoration 

Project. Logistical support was kindly provided by Cheryl Strong, Eric Mruz, Laura Valoppi, John 

Bourgeois, and John Krause, and the staffs of the Don Edwards San Francisco Bay National Wildlife 

Refuge and Eden Landing Ecological Reserve. We thank the following U.S. Geological Survey, Dixon 

Field Station staff who helped with this research: Tabitha McKinney, Trevor Watts, Jessica LaCoss, 

Nina Hill, Jarred Barr, Kristen Boysen, Sarah Flaherty, Nicolette Roach, and Camille Yabut. 
8 

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9 

Figure 1. Location and final nest fate of American Avocet (Recurvirostra americana) nests at restored Pond SF2, 

south San Francisco Bay, California, 2011–12. The 30 newly constructed islands are outlined in white.
10 

A)

B)

Figure 2. American Avocet (Recurvirostra americana) daily nest survival (A) and nest success (B) were lower in 

nests located farther from the highway (State Route 84), South San Francisco Bay, California. Solid line 

represents predicted values, and dashed lines are upper and lower 95% confidence intervals.
11 

Table 1. Spatial distribution and final nest fate of American Avocet (Recurvirostra americana) nests relative to potential disturbance features at 

restored Pond SF2, south San Francisco Bay, California, 2011–12. 

[Mean and standard errors are provided for all statistics. Number of nests used to estimate clutch size was a subset of nests found early in incubation (to reduce 

errors associated with partial clutch depredation) and are provided within parentheses. The final row provides average distances to possible disturbance features 

for all available nesting habitats within SF2] 

Final nest 

status Year Number of nests

Nest

initiation date Clutch size

Distance to

(in meters):

Berm Highway (State

Route 84) Levee Platform Trail

Successful 2011 109 (90) April 29 ±2 days 3.77 ±0.06 142 ±8 317 ±11 190 ±6 306 ±10 216 ±7

2012 0 (0) – – – – – – – 

Average 109 (90) April 29 ±2 days 3.77 ±0.06 142 ±8 317 ±11 190 ±6 306 ±10 216 ±7

Unsuccessful 2011 57 (37) May 23 ±3 days 2.92 ±0.18 140 ±14 355 ±17 185 ±8 334 ±16 232 ±11

2012 4 (0) May 5 ±12 days — 189 ±56 270 ±35 191 ±37 298 ±55 207 ±41

Average 61 (37) May 22 ±3 days 2.92 ±0.18 143 ±14 349 ±16 185 ±8 331 ±15 231 ±10

ALL 2011 166 (127) May 7 ±2 days 3.52 ±0.08 141 ±8 330 ±9 188 ±5 316 ±9 222 ±6

ALL 2012 4 (0) May 5 ±12 days — 189 ±56 270 ±35 191 ±37 298 ±55 207 ±41

ALL Average 170 (127) May 7 ±2 days 3.52 ±0.08 142 ±7 329 ±9 188 ±5 315 ±9 221 ±6

All Available Habitat 132 ±0.4 333 ±0.6 172 ±0.3 349 ±0.5 230 ±0.4
12 

Table 2. Model selection results for effects of potential disturbance features on daily nest survival of American Avocets (Recurvirostra americana) at 

restored Pond SF2, south San Francisco Bay, California, 2011–12. 

[Model structure: The + denotes an additive effect. k: The number of parameters in the model, including the intercept and variance. AICc: Akaike's Information 

Criterion (AICc). ΔAICc: The difference in the value between AICc of the current model and the value for the most parsimonious model. Akaike weight 

(wi):The likelihood of the model given the data, relative to other models in the candidate set (model weights sum to 1.0). Cumulative model weight: The 

cumulative weight of evidence for the top models (model weights sum to 1.0). Evidence ratio: The weight of evidence that the top model is better than the top

model, given the candidate model set. Only models with model weight greater than 0.001 and base model (NestAge only) are shown] 

Model structure k -2(LogLikelihood) AICc ΔAICc Model weight

Cumulative 

model 

weight

Evidence ratio

NestAge + InitiationDate + DistanceToHighway 5 351.648 361.674 0.000 0.308 0.308 1.000

NestAge + NestAge2 + InitiationDate + DistanceToHighway 6 349.872 361.908 0.235 0.274 0.582 1.124

NestAge + InitiationDate 4 356.203 364.220 2.546 0.086 0.668 3.572

NestAge + NestAge2 + InitiationDate 5 354.743 364.769 3.095 0.066 0.733 4.700

NestAge + InitiationDate + DistanceToTrail 5 355.535 365.561 3.887 0.044 0.778 6.985

NestAge + InitiationDate + DistanceToBerm 5 355.758 365.783 4.110 0.039 0.817 7.805

NestAge + NestAge2 + InitiationDate + DistanceToTrail 6 353.943 365.979 4.305 0.036 0.853 8.606

NestAge + NestAge2 + InitiationDate + DistanceToBerm 6 354.047 366.083 4.410 0.034 0.887 9.069

NestAge + InitiationDate + DistanceToPlatform 5 356.136 366.162 4.488 0.033 0.919 9.432

NestAge + InitiationDate + DistanceToLevee 5 356.189 366.215 4.541 0.032 0.951 9.684

NestAge + NestAge2 + InitiationDate + DistanceToPlatform 6 354.668 366.704 5.031 0.025 0.976 12.371

NestAge + NestAge2 + InitiationDate + DistanceToLevee 6 354.742 366.778 5.105 0.024 1.000 12.837

NestAge 3 394.596 400.607 38.933 0.000 1.000 2.85E+08

 
13 

Table 3. Relative variable importance metrics for effects of potential disturbance features on daily nest survival of 

American Avocets (Recurvirostra americana) at restored Pond SF2, south San Francisco Bay, California, 2011–12. 

[Rows in bold indicate variables with some support as important variables influencing nest survival. SE, standard error]

Variable

Prior variable 

weight 

(P0)

Parameter 

likelihood

(P)

Variable 

importance

Model average 

coefficient

SE modelaveraged 

coefficient

NestAge 1.000 1.000 — 0.083 0.066

DayofYear 0.500 1.000 17.762 -0.039 0.007

DistanceToHighway 0.167 0.582 1.939 -0.002 0.001

NestAge2 0.500 0.458 -0.169 -0.004 0.003

DistanceToTrail 0.167 0.080 -0.835 -0.001 0.002

DistanceToBerm 0.167 0.073 -0.926 0.001 0.001

DistanceToPlatform 0.167 0.058 -1.187 0.000 0.001

DistanceToLevee 0.167 0.056 -1.220 0.000 0.002

 
14 

Table 4. Model selection results for effects of potential disturbance features on clutch size of American Avocets 

(Recurvirostra americana) at restored Pond SF2, south San Francisco Bay, California, 2011–12. 

[Model structure: The + denotes an additive effect. k: The number of parameters in the model, including the intercept and 

variance. AICc: Akaike's Information Criterion (AICc). ΔAICc: The difference in the value between AICc of the current 

model and the value for the most parsimonious model. Akaike weight (wi):The likelihood of the model given the data, 

relative to other models in the candidate set (model weights sum to 1.0). Cumulative model weight: The cumulative weight 

of evidence for the top models (model weights sum to 1.0). Evidence ratio: The weight of evidence that the top model is 

better than the top model, given the candidate model set. Only models with model weight greater than 0.001 and base model 

(NestAge only) are shown] 

Model k -2(LogLikelihood) AICc ΔAICc Model 

weight

Cumulative 

model 

weight

Evidence 

ratio

InitationDate + DistanceToLevee 4 299.104 307.432 0.000 0.392 0.392 1.000

InitationDate 3 302.513 308.708 1.276 0.207 0.599 1.893

InitationDate + DistanceToHighway 4 300.767 309.095 1.663 0.171 0.770 2.297

InitationDate + DistanceToBerm 4 302.192 310.520 3.089 0.084 0.853 4.685

InitationDate + DistTrail 4 302.438 310.766 3.334 0.074 0.927 5.297

nitationDate + DistanceToPlatform 4 302.509 310.837 3.405 0.071 0.999 5.489

DistanceToLevee 3 315.165 321.360 13.928 0.000 0.999 1,058.097

DistanceToHighway 3 315.195 321.390 13.958 0.000 1.000 1,073.797

Intercept Only 2 319.052 323.149 15.717 0.000 1.000 2,587.730

DistanceToPlatform 3 318.093 324.288 16.857 0.000 1.000 4,574.904

DistanceToTrail 3 318.370 324.566 17.134 0.000 1.000 5,254.958

DistanceToBerm 3 318.770 324.965 17.533 0.000 1.000 6,415.981
15 

Table 5. Relative variable importance metrics for effects of potential disturbance features on clutch size of 

American Avocets (Recurvirostra americana) at restored Pond SF2, south San Francisco Bay, California, 2011–12. 

[Rows in bold indicate variables with some support as important variables. SE, standard error] 

Variable

Prior variable 

weight

(P0) 

Parameter 

likelihood

(P) 

Variable 

importance

Model average 

coefficient

SE modelaveraged 

coefficient

InitiationDate 0.500 0.999 6.804 -0.011 0.003

DistanceToLevee 0.167 0.392 1.172 0.002 0.001

DIstanceToHighway 0.167 0.171 0.031 -0.001 0.001

DistanceToBerm 0.167 0.084 -0.783 -4.48E-04 0.001

DistanceToTrail 0.167 0.074 -0.916 -2.52E-04 0.001

DistanceToPlatform 0.167 0.072 -0.954 3.96E-05 0.001

Table 6. Model selection results for the effects of potential disturbance features on nest initiation date of American 

Avocets (Recurvirostra americana) at restored Pond SF2, south San Francisco Bay, California, 2011–12. 

[Model structure: The + denotes an additive effect. k: The number of parameters in the model, including the intercept and 

variance. AICc: Akaike's Information Criterion (AICc). ΔAICc: The difference in the value between AICc of the current 

model and the value for the most parsimonious model. Akaike weight (wi):The likelihood of the model given the data, 

relative to other models in the candidate set (model weights sum to 1.0). Cumulative model weight: The cumulative weight 

of evidence for the top models (model weights sum to 1.0). Evidence ratio: The weight of evidence that the top model is 

better than the top model, given the candidate model set. Only models with model weight greater than 0.001 and base model 

(NestAge only) are shown] 

Model k -2(LogLikelihood) AICc ΔAICc 

Model 

weight

Cumulative 

model 

weight

Evidence 

ratio

DistanceToPlatform 3 1,563.974 1,570.120 0.000 0.970 0.970 1.000

DistanceToHighway 3 1,573.508 1,579.653 9.533 0.008 0.978 117.522

Intercept Only 2 1,575.644 1,579.717 9.597 0.008 0.986 121.329

DistanceToTrail 3 1,574.104 1,580.249 10.129 0.006 0.992 158.340

DistanceToLevee 3 1,574.540 1,580.686 10.566 0.005 0.997 196.959

DistanceToBerm 3 1,575.601 1,581.746 11.627 0.003 1.000 334.718
16 

Table 7. Relative variable importance metrics for effects of potential disturbance features on nest initiation date of 

American Avocets (Recurvirostra americana) at restored Pond SF2, south San Francisco Bay, California, 2011–12. 

[Rows in bold indicate variables with some support as important variables. SE, standard error]

Variable

Prior variable 

weight 

(P0)

Parameter 

likelihood

(P)

Variable 

importance

Model average 

coefficient

SE modelaveraged 

coefficient

DistanceToPlatform 0.167 0.970 5.079 0.060 0.017

DistanceToHighway 0.167 0.008 -3.180 0.024 0.017

DistanceToTrail 0.167 0.006 -3.480 0.033 0.026

DistanceToLevee 0.167 0.005 -3.699 -0.032 0.031

DistanceToBerm 0.167 0.003 -4.232 0.004 0.021
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Publishing Network, Tacoma Publishing Service Center

For more information concerning the research in this report, contact the

 Director, Western Ecological Research Center

U.S. Geological Survey

3020 State University Drive East

Sacramento, California 95819 

http://werc.usgs.gov/
Ackerman and others—Effects of Human Disturbance on Waterbird Nesting Effort South San Francisco Bay, California—Open-File Report 2014–1223

ISSN 2331-1258 (online)

http://dx.doi.org/10.3133/ofr20141223