Off‐road vehicles affect nesting behaviour and ...simons/Borneman_et_al-2016-Ibis.pdf · Off-road vehicles affect nesting behaviour and reproductive success of American Oystercatchers

Off-road vehicles affect nesting behaviour andreproductive success of American Oystercatchers

Haematopus palliatusTRACY E. BORNEMAN,1* ELI T. ROSE1 & THEODORE R. SIMONS2

1North Carolina Cooperative Fish and Wildlife Research Unit, Department of Applied Ecology, North Carolina StateUniversity, Raleigh, NC 27695, USA

2U.S. Geological Survey, North Carolina Cooperative Fish and Wildlife Research Unit, Department of AppliedEcology, North Carolina State University, Raleigh, NC 27695, USA

As human populations and associated development increase, interactions betweenhumans and wildlife are occurring with greater frequency. The effects of these interac-tions, particularly on species whose populations are declining, are of great interest toecologists, conservationists, land managers and natural resource policy-makers. TheAmerican Oystercatcher Haematopus palliatus, a species of conservation concern in theUSA, nests on coastal beaches subject to various forms of anthropogenic disturbance,including aircraft overflights, off-road vehicles and pedestrians. This study assessed theeffects of these human disturbances on the incubation behaviour and reproductive suc-cess of nesting American Oystercatchers at Cape Lookout National Seashore, on theAtlantic coast of the USA. We expanded on-going monitoring of Oystercatchers at CapeLookout National Seashore by supplementing periodic visual observations with continu-ous 24-h video and audio recording at nests. Aircraft overflights were not associated withchanges in Oystercatcher incubation behaviour, and we found no evidence that aircraftoverflights influenced Oystercatcher reproductive success. However, Oystercatchers wereon their nests significantly less often during off-road vehicle and pedestrian events thanthey were during control periods before the events, and an increase in the number ofoff-road vehicles passing a nest during incubation was consistently associated with signifi-cant reductions in daily nest survival (6% decrease in daily nest survival for a one-vehicleincrease in the average number of vehicles passing a nest each day; odds ratio = 0.94;95% confidence interval (CI) 0.90, 0.98) and hatching success (12% decrease in hatchingsuccess for a one-vehicle increase in the average number of vehicles passing a nest eachday; odds ratio = 0.88; 95% CI 0.76, 0.97). Management of vehicles and pedestrians inareas of Oystercatcher breeding is important for the conservation of American Oyster-catchers.

Keywords: aircraft, audio/video recording, birds, human disturbance, nest success, pedestrians.

Anthropogenic disturbance of wildlife is anincreasingly important issue in biodiversity conser-vation (Gill 2007, Sutherland 2007). As humanpopulations increase, a growing number of interac-tions between humans and wildlife may result inanimal population declines. Declining shorebird

populations in many parts of the world (Butchartet al. 2010) may be linked to increased humanactivity disturbing breeding, leading to reducedreproductive success (Flemming et al. 1988, Ens &Underhill 2014).

Disturbance that alters breeding behaviour canhave long-term consequences for avian productiv-ity. Nesting success may decrease with higher*Corresponding author.

Email: [email protected]

Published 2016. This article is a U.S. Government work and is in the public domain in the USA.

Ibis (2016), 158, 261–278

levels of human disturbance (Robert & Ralph1975, Tremblay & Ellison 1979, Safina & Burger1983). Along with direct destruction of eggs (Laf-ferty 2001, Sabine et al. 2006), flushing anddecreased nest attendance during times of humandisturbance (Verhulst et al. 2001, Baudains &Lloyd 2007) can lead to a higher incidence of eggloss (Robert & Ralph 1975, Tremblay & Ellison1979, Anderson & Keith 1980), presumably frompredation and decreased egg viability resultingfrom environmental exposure. Disturbance is alsoassociated with reductions in clutch size (Halfwerket al. 2011, Samraoui et al. 2012) and nest aban-donment (Tremblay & Ellison 1979, Safina & Bur-ger 1983), displacing birds and decreasing theamount of suitable nesting habitat (Erwin 1980,Carney & Sydeman 1999). However, assessmentsof anthropogenic disturbance often involve short-term, infrequent or opportunistic observations ofresponses to human activities.

Understanding the effects of anthropogenic dis-turbance is particularly relevant for species ofconservation concern, including shorebirds breed-ing in coastal areas that often experience heavyuse by humans. Vehicles and pedestrians on NovaScotia beaches altered Piping Plover Charadriusmelodus breeding adult and chick behaviour andwere correlated with decreased chick survival(Flemming et al. 1988). Humans were the mostfrequent cause of disturbance to brooding HoodedPlovers Thinornis rubricollis in Victoria, Australia,altering adult behaviour and potentially affectingsurvival of chicks (Weston & Elgar 2005).Reduced nesting and fledging success and aban-donment of breeding areas by Black SkimmersRynchops niger were also correlated with higherlevels of anthropogenic disturbance in New York,USA (Safina & Burger 1983). Human recreationpressure was associated with increased chick lossin Snowy Plovers Charadrius nivosus in northernCalifornia, USA (Ruhlen et al. 2003), while sitesprotected from human disturbance in Santa Bar-bara, California, USA, were rapidly colonized bySnowy Plovers that bred successfully (Laffertyet al. 2006).

However, not all birds show clear disturbanceresponses to human activity. Black OystercatcherHaematopus bachmani productivity in Alaska,USA, was not strongly affected by low levels ofhuman recreation (Morse et al. 2006). Disturbanceeffects were ambiguous on Cape Peninsula, SouthAfrica, where experimental disturbance conducted

by researchers decreased nest attendance ofWhite-fronted Plovers Charadrius marginatus butnest attendance was greater in areas of high humanrecreational activity (Baudains & Lloyd 2007).There is no conclusive evidence of the effect ofhuman activity on birds, making further researchon human disturbance necessary.

There is also no consensus on how differenthuman activities affect different wildlife species.Human activity can come in a variety of forms,and along with ground-based disturbance fromvehicles and human pedestrians, aircraft may alsoaffect behaviour and breeding of birds, althoughdisturbance effects are not clear. Crested TernsSterna bergii showed alert behaviours to simulatedaircraft noise, but were rarely flushed by it (Brown1990), while Herring Gulls Larus argentatus wereflushed off nests during supersonic aircraft flyovers,causing significant egg loss (Burger 1981). Con-versely, birds in a mixed seabird colony on thecoast of Scotland showed almost no response toaircraft flyovers (Dunnet 1977). It is thereforeimportant for ecologists, land managers and policy-makers to understand species-specific responses todifferent human activities and to make every effortto link these responses to reproductive success.

Human activities and development in coastalareas are the greatest concern for oystercatcher(Haematopodidae) conservation worldwide (Ens &Underhill 2014). Summers and Cooper (1977)and Hockey (1983) suggested that human pres-ence and off-road vehicles were major threats tobreeding African Black Oystercatchers Haematopusmoquini, with later research suggesting an associa-tion between human activity and increased egg,nest and chick loss of this species (Jeffrey 1987,Tjørve & Underhill 2008). Human disturbance hasalso been identified as a major cause of egg loss ofthe South Island Pied Oystercatcher Haematopusfinschi (Ens & Underhill 2014), and it may haveplayed a significant role in the extinction of theCanarian Black Oystercatcher Haematopus meade-waldoi (Hockey 1987).

The American Oystercatcher Haematopus pal-liatus is a species of high concern in the UnitedStates Shorebird Conservation Plan (Brown et al.2001) and the target of a variety of state and fed-eral conservation efforts (U.S. Fish and WildlifeService 2004, American Oystercatcher WorkingGroup & National Fish and Wildlife Foundation2008, North Carolina Wildlife Resources Commis-sion 2008). Declining populations along the


262 T. E. Borneman et al.

Atlantic coast of the USA are associated with habi-tat loss and with disturbance and predation associ-ated with human activities (Mawhinney et al.1999, Nol et al. 2000, Davis et al. 2001, AmericanOystercatcher Working Group et al. 2012).Ground-based human activities have been shownto affect incubation behaviour, nest-site selection,nest failure and chick mortality of American Oys-tercatchers (Novick 1996, Davis 1999, McGowan& Simons 2006, Sabine et al. 2008, Schulte 2012),although aircraft effects on Oystercatchers areunderstudied. To fill this gap, we used a novelapproach to conduct an extensive assessment ofthe effects of all human activities occurring in theenvironment, including aircraft overflights, off-roadvehicles and pedestrians, on the incubation beha-viour and reproductive success of nesting Ameri-can Oystercatchers at Cape Lookout NationalSeashore, on the Atlantic coast of the USA. Wesupplemented periodic visual observations of 62nests of 47 pairs of nesting American Oystercatch-ers with continuous 24-h video and audio record-ing at nests for the full incubation period,generating a 48 000-h comprehensive record ofhuman activity and American Oystercatcher beha-viour in the nesting environment. This approachallowed us to quantify the frequency and type ofall disturbance events and the specific behaviouralresponses of known pairs of American Oyster-catchers to specific disturbance events, and toidentify definitive causes of nest failures for mostnests, which in turn allowed us to probe theunderlying mechanisms of population-level effects.We are unaware of any other study conducting asexhaustive an assessment of human disturbance,measuring responses of birds to such a wide arrayof anthropogenic activities and with such a highlevel of sampling intensity and resolution.

METHODS

Study area

We conducted field research in 2010 and 2011 atNorth Core Banks (34°57015″N, 76°11018″W),Cape Lookout National Seashore, which is locatedalong the central coast of North Carolina, USA,and managed by the National Park Service(Fig. 1). North Core Banks is a narrow barrierisland, just under 37 km (23 miles) in length, thatlies between the Atlantic Ocean and Core Sound.The island habitat consists of open sandy beaches

on the ocean side backed by dunes and sand flats.The sand flats may extend across the width of theisland from the ocean to Core Sound, or occur aspatches of bare sand between the outer beach andthe primary dunes. Grasses, shrub thickets andoccasional areas of low trees occur between theprimary dunes and Core Sound. The island ismostly undeveloped and natural habitats predomi-nate, making it an important breeding location forshorebirds, colonial waterbirds and sea turtles.

North Core Banks is accessible only by boat. Avehicle/pedestrian ferry near the southern end ofthe island and a pedestrian-only ferry at the north-ern tip of the island provide public access to parkvisitors. Driving is permitted on the beach for thefull length of the island. A primitive unpaved sandroad behind the primary dunes, which extendsfrom island mile 4 to island mile 6, and again frommile 7 to mile 18.5, provides vehicle access duringperiods of high tides or beach closures, but vehicletraffic is most often concentrated on the openbeach. The National Park Service extended thisroad prior to the 2011 bird breeding season toinclude a section from island mile 19.3 to mile20.9.

Aircraft fly regularly in the vicinity of NorthCore Banks. Cape Lookout lies directly beneath amilitary operations area airspace, Core Banks Mili-tary Operations Area (Core MOA), which is man-aged by the United States Marine Corps.Historically, the minimum altitude for tacticalspeed operations (aircraft flying > 250 knots) inthe Core MOA was 3048 m (10 000 feet). How-ever, in 2009 the National Park Service and theUnited States Marine Corps agreed to experimen-tally lower the minimum altitude to 914.4 m(3000 feet) to evaluate the effects of high-speedlow-altitude overflights on several species of birdsbreeding in the National Seashore. Airspaces sur-rounding the Core MOA have fewer altituderestrictions and are used regularly by both militaryand civilian aircraft which are audible on NorthCore Banks.

Study species

The American Oystercatcher is a member of thefamily Haematopodidae, which comprises 11extant species found in coastal habitats worldwide(Ens & Underhill 2014). Recent population esti-mates of the American Oystercatcher in the east-ern USA indicate a population size of


Effects of human activity on nesting American Oystercatchers 263

approximately 11 000 individuals (Brown et al.2005). Population trends differ between differentparts of the American Oystercatcher’s range, withincreases reported in the northeast region and Vir-ginia and declines in the mid-Atlantic to southeastregions (American Oystercatcher Working Groupet al. 2012, Clay et al. 2014). In the USA, Ameri-can Oystercatchers breed from Maine to Floridaon the Atlantic coast and along the Gulf of Mexicofrom Florida to Mexico (American OystercatcherWorking Group et al. 2012). Cape LookoutNational Seashore supports approximately 65breeding pairs of American Oystercatchers annu-ally (National Park Service 2014). Oystercatchersarrive at Cape Lookout, form pairs and establishbreeding territories in early April. Pairs are highlyterritorial and exhibit strong nest-site and matefidelity, frequently returning to the same territoryyear after year (Schulte 2012). Most nests at CapeLookout are found on the open beach or adjacentprimary dunes, but American Oystercatchers alsonest on sand flats and sound-side marshes.Clutches of one to four eggs, laid in a shallowscrape on the ground, are incubated by both adults

for an average of 27 days until hatching. Pairs mayattempt multiple clutches in a single breeding sea-son if early nests are destroyed before chickshatch. The semi-precocial chicks leave the nestshortly after hatching, generally within a fewhours, but rely almost completely on their parentsfor food and protection until they fledge about35 days after hatching.

Field methods

Productivity monitoringWe conducted surveys of nesting American Oys-tercatchers on North Core Banks during thebreeding season from early April to early Augustin 2010 and 2011, continuing annual productiv-ity monitoring that has been on-going at NorthCore Banks since 1997 (National Park Service2014). Nesting American Oystercatchers werelocated visually by driving the length of theisland and identifying birds exhibiting breedingor territorial behaviours. We then located nestsby observing the birds, following their tracks orsystematically searching areas of suspected breed-

mile 9

mile 7

mile 5

mile 3

mile 1

mile 21

mile 19

mile 17

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mile 11

North Core Banks

American Oystercatcher nestsmonitored with video/audio

0 1 2 3 40.5Kilometers

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United States

Cape LookoutNational Seashore

South Core Banks

ShacklefordBanks

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0 8 16 24 324Kilometers

North Core Banks

Figure 1. Location map of the study area, North Core Banks, Cape Lookout National Seashore, along the Atlantic Ocean coast ofthe USA. Distance markers along the island are indicated and black dots represent American Oystercatcher nests that were moni-tored with video and audio recording equipment.



ing activity. Many of the breeding AmericanOystercatchers had individually recognizablealphanumeric-coded leg rings, allowing us toattribute nests and re-nests to specific pairs. Ifbirds were unmarked, all nests found in the sameterritory were attributed to the unmarked pairoccupying that territory.

We classified nesting habitat as either open sandor dune. Open sand habitats included the openbeach and sand flats where the terrain was flat andopen with minimal vegetation and high visibility.Dune habitats were areas of varying and elevatedterrain with more vegetation and more limitedvisibility.

We monitored nests to estimate the distribu-tion, abundance, productivity, survival and incuba-tion behaviour of American Oystercatchers, and todetermine levels of human activity in the nestingenvironment. Nest monitoring was conducted bydirect observation every 1–3 days and with contin-uous video and audio recording until nests failedor eggs hatched. If a nest failed, we determinedthe cause of nest failure from evidence at the nest-site or by reviewing video recordings. If a nesthatched, we located and observed chicks every 1–2 days to determine chick survival and fledgingdates. Research was focused mainly on the incuba-tion period of the breeding cycle; however, datafrom the brood-rearing stage were also included toassess the effects of human activity on reproduc-tive success.

We compared data on annual park visitation(during American Oystercatcher breeding months)and annual American Oystercatcher productivityusing visitation data collected by the National ParkService (National Park Service 2013).

Vehicle closuresThe National Park Service manages vehicle activityon North Core Banks with signage and closedareas to reduce disturbance to breeding shorebirds.We classified vehicle management practices aroundAmerican Oystercatcher nests in 2010 and 2011into five categories. Nest-only closures were smallclosed areas posted with signs along a 5-m radiusaround active nests. Full closures were large areasclosed to protect colonial nesting birds, and nestingPiping Plovers and American Oystercatchers; vehi-cles were excluded inside the closure but theycould drive along portions of the perimeter. Rampclosures rerouted vehicles around active nests onthe oceanfront beach to the interior sand road

behind the dunes. Drive-through closures preventedvehicles from stopping in the vicinity of nests, butallowed driving past nests on the oceanfront beach.Vehicles were not managed (no closure) at nestslocated in dune or other habitats away fromapproved vehicle routes. Vehicle managementaround the nests occasionally changed during theincubation period, so we assigned the vehicle man-agement practice classifications to all AmericanOystercatcher nests based on the vehicle manage-ment that was in effect for the majority of theincubation period of the nest. In 2011, we alsoassigned these classifications to nests on a dailybasis. The distance from nests to vehicles varied(from approximately 5 to 800 m) in all closurecategories depending on the location of the nestand the boundary of the closure.

Monitoring of anthropogenic activity, incubationbehaviour and nest survivalWe monitored the incubation behaviour of Ameri-can Oystercatchers and identified and quantifiedhuman activity in the vicinity of nests during the2010 and 2011 breeding seasons using continuousdigital video and audio recording (Videos S1 andS2). We were unable to monitor all nests withrecording equipment and therefore used a strati-fied sampling scheme in which we randomlyselected breeding pairs for monitoring from stratadetermined by location along the length of theisland, location relative to the primary dunes andvehicle closure status. We compared the hatchingsuccess rate of the recorded nests to the hatchingsuccess rate of the nests we could not record.

Video cameras monitored incubating AmericanOystercatcher behaviour and human activity inthe vicinity of nests. Video recordings also pro-vided information about incubation rates, inter-and intraspecific interactions, nest predation eventsand timing of hatching. Cameras were placed atnests as soon as possible after nests were at fullclutch (no additional eggs were laid for three con-secutive days) and recorded continuously 24 h aday until nests either failed or hatched. The videomonitoring system comprised a closed-circuit secu-rity camera with infrared capability to allowrecording at night, a digital video recorder, two12-V 35-Ah absorbent glass mat (AGM) sealedlead acid batteries and a voltage regulator (Fig. 2).We housed all components in a 5-gallon plasticbucket with a waterproof lid for protection,weatherproofing and transportability. We replaced



camera units in the field every 7 days to downloadrecorded video and replace batteries. We posi-tioned video cameras approximately 5 m fromnests with the adjacent beach habitat in the fieldof view so we could identify as many sources ofhuman activity and potential disturbance (off-roadvehicles, pedestrians, predators, etc.) as possible(Fig. 2). As a consequence of differences in thelandscape around nests, the total area surveyed byvideo recordings varied somewhat among nests(visibility distances around nests ranged fromapproximately 50 to 300 m).

Audio recorders recorded ambient sound levelsand noise events at nests continuously 24 h perday until the nests either failed or hatched.These recordings provided a record of both natu-ral and anthropogenic sounds in the immediatevicinity of nesting American Oystercatchers. Wemounted Samson Zoom H2 digital audio recor-ders (Samson Technologies Corp., Hauppauge,NY, USA) approximately 1.5 m above theground adjacent to nests (Fig. 2). Video andaudio recording times were synchronized using asatellite-calibrated watch. We replaced audiorecorders in the field every 3–4 days to downloadrecorded audio and replace batteries. We cali-brated the Zoom H2 recordings using a highlysensitive and accurate Larson Davis Model 831sound level meter (Larson Davis, Depew, NY,USA) to ensure the accuracy of our sound levelmeasurements. The National Park Service NaturalSounds and Night Skies Division processed the

calibration data as described by Mennitt andFristrup (2012).

Sampling video/audio recordings

We collected approximately 48 000 h of simulta-neous video and audio recordings during the 2010and 2011 breeding seasons. Nests were recordedfor an average of 14 days and a maximum of28 days. Starting on the day following deploymentof recording equipment at a nest (i.e. the first full24-h day of recording), we reviewed all video andaudio recording files within a 24-h period for everyfourth day of monitoring (we sampled 226 record-ing days; approximately 25% or 12 000 h of thetotal video and audio recordings). From these sub-samples, we noted every occasion when an Ameri-can Oystercatcher left or returned to its nest,every incident of human activity (either heard onthe audio recordings, seen on the video recordingsor both), and the behaviour of the incubatingAmerican Oystercatcher before and during thehuman activity events. A human activity eventwas defined as the time at which an incident ofhuman activity could first be seen or heard on therecordings to the time it was no longer visible orheard. We included all human activity eventsdetected by either the video or the audio recor-ders. Most of the human activities were onlydetected either by video or by audio because air-craft very infrequently flew in the field of view ofthe video cameras and, because of the louder

(a) (b) (c)

Figure 2. Video and audio recording equipment used to monitor incubating American Oystercatchers and surrounding human activityat North Core Banks, Cape Lookout National Seashore, USA. The video recording system consisted of a camera, digital video recor-der and batteries encased in a 5-gallon plastic bucket (a) that was placed near active Oystercatcher nests (b). The audio recordingsystem consisted of a digital audio recorder mounted within a windscreen 1 m above the ground, which was powered by a batteryplaced in a plastic bucket (c). Audio recorders were also placed in the vicinity of active nests.



ambient noise levels of the coastal environment,pedestrians and vehicles were often not heard onthe audio recordings. In addition, the UnitedStates Marine Corps, Cherry Point Naval Air Sta-tion, provided information on the timing, location,speed and altitude of military overflights throughthe Core MOA airspace above Cape LookoutNational Seashore. We used this information withthe time stamps on the audio and video recordingsto identify the Core MOA flights on the record-ings and assess them independently from othertypes of aircraft. Analyses were conducted byreviewing all video and audio collected duringknown Core MOA overflights; recording equip-ment at nests reliably detected 86% of Core MOAflights at a straight-line distance of 5000 m or lessfrom recording devices, 79% of flights at 7000 mor less, 69% of flights at 9000 m or less and 64%of flights at 11 000 m or less.

We quantified the behavioural response ofAmerican Oystercatchers to human activity as theproportion of observations in which American Oys-tercatchers were on (as opposed to off) their nestsduring human activity events. We compared this tothe proportion of observations in which AmericanOystercatchers were on their nests 20 min beforethe human activity events as a control. We classifiedan American Oystercatcher as on the nest if it wassitting on or standing over the eggs at the instant ofthe peak of the human activity event (i.e. when thehuman stimulus was closest to the nest or soundlevels were highest). This behavioural assessmentwas repeated at the instant exactly 20 min beforethe peak of the human activity event (as the con-trol). We also quantified the number of timesAmerican Oystercatchers departed from their nestseach day (stepped off and away from their nests)and the per cent of each day that American Oyster-catchers attended their nests (daily nest atten-dance). We classified an American Oystercatcher asattending the nest whenever it was sitting on orstanding over the eggs.

We used motion detection software (createdspecifically for our project by a student at NorthCarolina State University) to process the originalvideo recordings and extract frames showingAmerican Oystercatcher and human activity atand around the nest. The motion detection soft-ware was found to be 93% accurate by reviewingsegments of original recordings for comparison tomotion detection results; however, in cases wheremotion-detected images produced ambiguous

results, we watched the complete video recordingto document activity at the nest. We used audio-recording processing software (AUDIO2NVSPL andACOUSTIC MONITORING TOOLBOX, v1.3877), devel-oped by the Natural Sounds and Night Skies Divi-sion of the National Park Service (Joyce 2009), tocalculate sound level values for all human activityevents heard on audio recordings.

Statistical analyses

Unless stated otherwise, we conducted all statisti-cal analyses in R (R Development Core Team2011), applying a significance level of P < 0.05.

We used the program MARK (White & Burnham1999) to estimate nest survival (nests hatched/totalnests � se) and chick survival (chicks fledged/chicks hatched � se), and calculated breeding pro-ductivity (chicks fledged per breeding pair � se)estimates in Microsoft EXCEL. We used the pro-gram CONTRAST (Hines & Sauer 1989), an onlineprogram which compares survival estimates, tocompare nest survival and breeding productivityestimates during study years (2010–2011) to esti-mates for pre-study years (1999–2009). We testedfor associations between annual visitation at NorthCore Banks during the American Oystercatchernesting season (National Park Service 2013) andannual nest survival and productivity (chicksfledged per breeding pair) from 1998 to 2011using simple linear regression models.

We compared the hatching success (at least oneegg in the nest hatched a chick) of nests moni-tored with video and audio recording equipmentto the hatching success of nests that were notrecorded using a v2 test.

We used McNemar’s v2 tests for paired data tocompare the proportions of observations in whichOystercatchers were on their nests before (control)and during (treatment) human activity events.Each type of human activity was assessed individu-ally. Core MOA flights were divided into two cat-egories: low-altitude and high-altitude flights.High-altitude flights were ≥ 3048 m altitude; low-altitude flights were < 3048 m altitude, followingthe agreement of the National Park Service andU.S. Marine Corps to lower the minimum altitudeof Core MOA flights from 3048 to 914.4 m.

We used a generalized linear mixed model(mixed effects logistic regression), with humanactivity type and nesting habitat type as fixedeffects and nest (individual breeding pair) as a ran-



dom effect, to compare behaviour before andbehaviour during human activity events. Thisanalysis only included samples in which Oystercatch-ers were on their nests 20 min before human activityevents occurred. We used a similar mixed effects logis-tic regression model to compare the effects of the CoreMOA flight altitude on the behavioural responses ofAmerican Oystercatchers. The model included alti-tude as a categorical fixed effect (low vs. high altitude),habitat type as a fixed effect and nest (individualbreeding pair) as a random effect. The interactionbetween altitude and habitat was not significant, so itwas excluded from the model.

We assessed how the daily amount of humanactivity in the vicinity of nests (because of differ-ences in the landscape around nests, the total areasurveyed by video recordings varied somewhatamong nests) affected the number of times Ameri-can Oystercatchers departed from their nests eachday using simple and multiple linear regression.

We compared the daily nest attendance ofhatched nests to that of failed nests using a Welch’st-test to account for the possibility of unequal vari-ances between samples. We tested for a relationshipbetween the amount of daily human activity anddaily nest attendance using simple and multiple lin-ear regression models, applying an arcsine squareroot transformation to daily nest attendance.

We analysed differences in the daily behaviour(nest attendance and departure rates) of AmericanOystercatchers nesting in areas of different types ofvehicle closures by comparing a linear mixed effectsmodel including closure type as a fixed effect andnest as a random effect to the null model (whichincluded only nest as a random effect) usingAkaike’s information criterion corrected for smallsample size (AICc; Burnham & Anderson 2002).Only nests from 2011 were incorporated in thisanalysis as we categorized vehicle closure type fornests on a daily basis in 2011 only. No nests in 2011were assigned the nest-only closure type.

We included variables for American Oyster-catcher behavioural responses, human activity,vehicle closure type and habitat type in a multiplelogistic regression model to assess the effect ofthese covariates on nest success. Daily nest survivalrates and the effects of covariates were assessedwith a logistic exposure model. The logistic expo-sure model accounts for biases associated withvariations in the age of discovery and exposureperiods of nests, and heterogeneity in daily survivalrates among nests, and it allows for the inclusion

of explanatory variables (Shaffer 2004, Shaffer &Thompson 2007). The effect of monitoring equip-ment at a nest on daily nest survival and hatchingsuccess was assessed separately from other nestcovariates because data for other covariates werecollected using the monitoring equipment, makingthem fully dependent. We used a significance levelof 0.05, and odds ratios with 95% confidenceintervals (CIs) to assess the magnitude of the effectof any significant explanatory variable.

RESULTS

Productivity

In 2010, we observed 31 American Oystercatcherpairs make 58 nesting attempts. Of these, 15 nestssuccessfully hatched 30 chicks, and 15 of thosechicks survived to fledging. In 2011, 32 pairs made54 nesting attempts. Of these, 18 nests success-fully hatched 37 chicks, and 24 of those chickssurvived to fledging.

Nest survival (nests hatched/total nests � se)and chick survival (chicks fledged/chicks hatched� se) were 0.259 � 0.059 and 0.500 � 0.091 in2010 and 0.333 � 0.064 and 0.649 � 0.078 in2011, respectively. Breeding productivity (chicksfledged per breeding pair � se) was 0.484 � 0.089in 2010 and 0.750 � 0.149 in 2011. Average nestsurvival during study years (0.340 � 0.041; 2010–2011) was higher than the average for pre-studyyears (0.280 � 0.059; 1999–2009), although thisdifference was not significant (v2 = 1.60, df = 1,P = 0.21). Average breeding productivity duringstudy years (0.617 � 0.133; 2010–2011) was sig-nificantly higher than the average for pre-studyyears (0.345 � 0.022; 1998–2009) (v2 = 6.50,df = 1, P = 0.01). We also calculated daily nest sur-vival rates using a logistic exposure model (Shaffer2004). The overall daily survival rate for all nestswas 0.966 � 0.004 (n = 112).

We found no relationship between annual visitationat North Core Banks and either annual nest survival(n = 13 years (1999–2011), R2 = 0.06, F1,11 = 0.65,P = 0.44) or annual productivity (n = 14 years(1998–2011), R2 =0.13, F1,12 =1.73, P = 0.21; Fig. 3).

Video and audio monitoring at nests

We monitored 62 nests (55% of 112 total nests; 33in 2010 and 29 in 2011) of 47 breeding pairs ofOystercatchers with video and audio recording



equipment (Fig. 1). Of these 62 nests, 24 success-fully hatched chicks and 38 failed. Hatching successat nests with recording equipment (0.39) was signif-icantly higher than hatching success at nests with-out recording equipment (0.18) (v2 = 4.76,P = 0.03). The presence of recording equipmentwas also significantly associated with increased dailynest survival (estimate � se = 0.56 � 0.24,Z = 2.40, P = 0.02). The odds of daily nest survivalwere 1.76 (95% CI 1.12, 2.77) times greater fornests with recording equipment than for those with-out. Nests with and without recording equipmentwere similarly distributed across habitat types: theproportion of nests in open sand (vs. dune) habitatswas 0.69 for recorded nests and 0.70 for non-recorded nests. The proportion of nests in each clo-sure type for recorded nests vs. non-recorded nests,respectively, was 0.37 and 0.38 in full closures,0.05 and 0.02 in nest-only closures, 0.16 and 0.20in no closures, 0.19 and 0.36 in drive-through clo-sures, and 0.23 and 0.04 in ramp closures.

Recording equipment malfunction and nest fail-ures resulted in 56 nests of 45 breeding pairs foranalyses. Not all 56 nests had data suitable for eachof the analyses; if fewer than 56 nests were used inan analysis, the number of nests used is reported.

Anthropogenic activity

Anthropogenic activities recorded in the nestingenvironment included Core MOA overflights

(military aircraft corresponding with reportedflights through the Core MOA; n = 290; mean/day � se = 0.5 � 0.1; Video S1), other militaryfixed-wing aircraft (military aircraft not reported asflying through the Core MOA; n = 1477; mean/day � se = 8.5 � 0.8), civilian fixed-wing aircraft(n = 492; mean/day � se = 2.9 � 0.2), rotary-wing aircraft (we could not differentiate militaryfrom civilian rotary-wing aircraft; n = 135; mean/day � se = 0.8 � 0.1), passenger vehicles(n = 2109; mean/day � se = 12.0 � 0.9), all-ter-rain vehicles (ATVs; single passenger; n = 1111;mean/day � se = 6.3 � 0.4; Video S2), utility-ter-rain vehicles (UTVs; all-terrain vehicles with twopassengers side by side; n = 211; mean/day � se = 1.2 � 0.1), and pedestrians (n = 154;mean/day � se = 0.9 � 0.3). We recorded anaverage (� se) of 34.0 � 1.5 human activityevents at nests each day (averaged over 56 video-monitored nests in 2010 and 2011).

Behavioural response

Oystercatchers were on their nests in about thesame proportion of observations before and duringmost types of aircraft events (low-altitude CoreMOA flight: n = 101, v2 = 0.06, P = 0.80; high-altitude Core MOA flight: n = 166, v2 = 0.28,P = 0.60; civilian fixed-wing: n = 492, v2 = 0.10,P = 0.76; rotary-wing: n = 135, v2 = 0, P = 1)(Fig. 4; Video S1). Oystercatchers were on their

Figure 3. Historical annual visitation during the American Oystercatcher breeding season, and American Oystercatcher nest survivaland productivity (chicks fledged per breeding pair) rates, at North Core Banks, Cape Lookout National Seashore, USA.



nests significantly more during military fixed-wingflights than before the flights (n = 1474,v2 = 5.31, P = 0.02) (Fig. 4) and significantly lessduring all types of off-road vehicle and pedestrianevents than they were before those eventsoccurred (passenger vehicle: n = 2101, v2 = 91.88,P < 0.01; ATV: n = 1109, v2 = 517.5, P < 0.01;UTV: n = 211, v2 = 34.46, P < 0.01; pedestrian:n = 154, v2 = 21.73, P < 0.01) (Fig. 4; Video S2).It took birds an average (� se) of 9.75 � 0.35 min(n = 1638 events occurring at 53 nests) to returnto their nests following human activity events. Thelongest return time following a human activityevent was 59.78 min (after passage of a passengervehicle), but 75% of birds returned to their nestswithin 8.83 min following a human activity event.

The type of human activity influenced theprobability that an incubating bird was off its nestduring human activity events (n = 5203 observa-tions from 53 nests, Z = 833.02, P < 0.01)(Fig. 5). Nesting habitat also appeared to influencethe probability that an incubating bird was off itsnest during human activity events (Z = 6.13,P < 0.01) (Fig. 5). A significant interactionbetween the two predictor variables suggests thatAmerican Oystercatchers nesting in open sandhabitats react differently to different types of

human activity from birds in dune habitats(v2 = 40.32, P < 0.01). Oystercatchers were morelikely to be off their nests during the passage of alltypes of off-road vehicles and pedestrians whennests were located in open sand areas (n = 39)than they were when nests were located in dunehabitats (n = 14), while the probability of anAmerican Oystercatcher being off its nest duringaircraft activity varied by aircraft type and nestinghabitat (Fig. 5). The altitude of the flights throughthe Core MOA (low vs. high) had no significanteffect on the probability that American Oyster-catchers were off their nests during the flights(n = 227 observations from 42 nests, Z = 0.20,P = 0.84).

Of all human activity types, only the dailynumber of ATV events occurring around a nestwas positively related to the daily number ofdepartures from the nest, explaining 8.7% of thevariation in departures (n = 174, R2 = 0.09,F1,172 = 16.34, P < 0.01).

Daily nest attendance averaged (� se)88.2 � 0.7% (21.2 � 0.2 h) of the day(n = 230 days for 55 nests). Nests that successfullyhatched had higher average (� se) daily nestattendance (89.7 � 1.0%; n = 23 nests) than neststhat failed (81.7 � 2.5%, n = 32 nests) (t = 2.97,

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

Low-al�tudeMOA Flight

High-al�tudeMOA Flight

Military Fixed-Wing

Civilian Fixed-Wing

Rotary-Wing PassengerVehicle

ATV UTV Pedestrian

(n = 101) (n = 166) (n = 1474) (n = 492) (n = 135) (n = 2101) (n = 1109) (n = 211) (n = 154)

Prop

or�o

n of

obs

erva

�ons

on

the

nest

(± se

)

Human ac�vity type

20 min.Before

During

Figure 4. The proportion of observations (� se) of American Oystercatchers on their nests during different types of human activityand the control proportion 20 min before those human activity events occurred at North Core Banks, Cape Lookout National Sea-shore, USA. Sample sizes include observations from 56 audio/video-monitored nests. MOA flights are military aircraft flying throughthe military operations area (Core MOA) over Cape Lookout National Seashore (high-altitude flights were ≥ 3048 m altitude, low-alti-tude flights were < 3048 m altitude); military fixed-wing aircraft are other military aircraft not reported as flying through the CoreMOA. ATVs are single-passenger all-terrain vehicles, and UTVs are side-by-side utility-terrain vehicles.



df = 40.89, P = 0.01). We found no relationshipbetween the average number of human activityevents per day and average daily nest attendance(n = 55 nests, R2 = 0.01, F1,53 = 0.63, P = 0.43).We also found no relationship between the num-ber of human activity events in a given day andthe daily nest attendance for that day(n = 175 days, R2 = 0.04, F1,173 = 0.11, P = 0.74).Daily nest attendance was not related to the num-ber of off-road vehicle events in a day (n = 175,R2 = 0.002, F1,173 = 0.35, P = 0.56). Of all humanactivity types, only rotary-wing aircraft showed anegative relationship between the daily number ofevents and daily nest attendance, although itexplained only 3% of the variation in attendance(n = 175, R2 = 0.03, F1,173 = 5.35, P = 0.02).

We found no evidence of a significant influenceof closure type on daily nest attendance of Ameri-can Oystercatcher pairs, as the null model outper-formed the model that incorporated the effects ofclosure type (null: AICc = �220.26; closure:AICc = �126.43). Relative to nests within full clo-sures, closure type had no effect on nest atten-dance (estimate � se: none, < 0.01 � 0.07,n = 7 days for two nests; drive-through,0.02 � 0.05, n = 27 days for eight nests; ramp,

�0.03 � 0.04, n = 44 days for 14 nests). Closuretype did, however, have a minimal influence onthe number of daily departures from the nest.Although the model that included closure typeoutperformed the null model (closure:AICc = 692.18; null: AICc = 1198.24), the param-eter estimates suggest that there was little differ-ence in the number of departures between fullyenclosed nests and those within other types of clo-sure (estimate � se: none, �3.97 � 4.31,n = 7 days for two nests; drive-through,2.08 � 2.87, n = 27 days for eight nests; ramp,1.56 � 2.66, n = 44 days for 14 nests).

Nest survival

We assessed the effects of several covariates onhatching success and daily nest survival (n = 48nests), including: the average number of aircraft(all aircraft types combined) events per day, theaverage number of off-road vehicle (all vehicletypes combined) events per day, the vehicle clo-sure type (type of management of human activityaround nests), the average number of times birdsleft their nests per day, the average daily nestattendance and nest habitat type. The average

Figure 5. Probability that American Oystercatchers were not on their nest during various types of human activity in open sand(n = 39 nests) and dune nesting (n = 14 nests) habitats at North Core Banks, Cape Lookout National Seashore, USA. Open sandareas are habitat such as the open beach and sand flats in which visibility is high; dune habitats are located within large dunes withmore limited visibility. MOA flights are military aircraft corresponding with reported flights through the military operations area (CoreMOA) above Cape Lookout National Seashore; military fixed-wing aircraft are other military aircraft not reported as flying through theCore MOA. ATVs are single-passenger all-terrain vehicles, and UTVs are side-by-side utility-terrain vehicles.



number of off-road vehicle events per day was theonly variable significantly correlated with daily nestsurvival (Table 1) and hatching success (Table 2),given the presence of the other variables. The oddsof a nest surviving each day decreased by 6% (odds

ratio 0.94, 95% CI 0.90, 0.98) and the odds ofsuccessful hatching of a nest decreased by 12%(odds ratio 0.88, 95% CI 0.76, 0.97) for a one-vehicle increase in the average number of vehiclespassing a nest each day.

Table 1. Logistic exposure model exploring factors potentially affecting the daily survival rate of American Oystercatcher nests atNorth Core Banks, Cape Lookout National Seashore, USA, in 2010 and 2011 (n = 48). All factors evaluated were included in thismodel.

Explanatory variable Estimate (se) Z P-valueOdds ratioa

(eEstimate)95% CI forodds ratio

Intercept 0.800 (2.627) 0.304 0.761Average daily aircraft events 0.013 (0.020) 0.660 0.509Average daily vehicle events �0.063 (0.021) �2.941 0.003* 0.939 0.902, 0.982Vehicle closureb

Nest-only 14.810 (929.137) 0.016 0.987None �1.373 (0.875) �1.570 0.116Drive-through 0.104 (0.847) 0.123 0.902Ramp �0.345 (0.575) �0.601 0.548

Average daily Oystercatcher departures 0.043 (0.055) 0.777 0.437Average daily nest attendance 0.038 (0.023) 1.653 0.098Habitatc

Within dunes �0.236 (0.740) �0.319 0.750

CI, confidence interval. *Significant at a significance level of P < 0.05. aOdds ratios were only calculated for variables that weresignificant. bVehicle closures (full: n = 14; nest-only: n = 3; none: n = 7; drive-through: n = 10; ramp: n = 14) were active vehiclemanagement by the National Park Service around shorebird breeding areas. See main text for descriptions of vehicle closure types.Full closure was used as the baseline level for the analysis, so does not appear in the analysis output above. cNest habitats wereclassified as open sand (n = 36) or within dunes (n = 12). See main text for descriptions of habitats. Open sand habitat was used asthe baseline level for the analysis, so does not appear in the analysis output above.

Table 2. Logistic regression analysis exploring factors potentially associated with American Oystercatcher nest hatching success atNorth Core Banks, Cape Lookout National Seashore, USA, in 2010 and 2011 (n = 48). All factors evaluated were included in thismodel.

Explanatory variable Estimate (se) Z P-valueOdds ratioa

(eEstimate)95% CI forodds ratio

Intercept �10.467 (9.035) �1.158 0.247Average daily aircraft events 0.076 (0.054) 1.409 0.159Average daily vehicle events �0.132 (0.062) �2.116 0.034* 0.877 0.757, 0.970Vehicle closureb

Nest-only 18.144 (2164.6) 0.008 0.993None �2.468 (1.583) �1.559 0.119Drive-through �0.173 (1.238) �0.140 0.889Ramp 0.158 (1.114) 0.142 0.887Average daily Oystercatcher departures 0.091 (0.094) 0.971 0.332Average daily nest attendance 0.099 (0.078) 1.277 0.201

Habitatc

Within dunes �0.311 (1.304) �0.239 0.811

CI, confidence interval. *Significant at a significance level of P < 0.05. aOdds ratios were only calculated for variables that weresignificant. bVehicle closures (full: n = 14; nest-only: n = 3; none: n = 7; drive-through: n = 10; ramp: n = 14) were active vehiclemanagement by the National Park Service around shorebird breeding areas. See main text for descriptions of vehicle closure types.Full closure was used as the baseline level for the analysis, so does not appear in the analysis output above. cNest habitats wereclassified as open sand (n = 36) or within dunes (n = 12). See main text for descriptions of habitats. Open sand habitat was used asthe baseline level for the analysis, so does not appear in the analysis output above.



DISCUSSION

American Oystercatchers responded differently todifferent types of human activities. Birds did notshow a significant behavioural response to most air-craft overflights, nor did we find an influence of air-craft on reproductive success. Oystercatchers alsoexhibited minimal increases in heart rate in responseto most aircraft overflights (Borneman et al. 2014). Itappears that either American Oystercatchers viewaircraft as a minimal threat or they have habituatedto the presence of aircraft in their nesting environ-ment. We were unable to assess the response ofAmerican Oystercatchers in fully undisturbed areaswith no aircraft overflights. A similar lack of beha-vioural response to aircraft, perhaps as a result ofhabituation, was noted in studies of nesting seabirds(Dunnet 1977), nesting raptors (Andersen et al.1989, Ellis et al. 1991, Trimper et al. 1998) andbreeding penguins (Hughes et al. 2008). Low-alti-tude flights were also not found to affect the repro-ductive success of Spotted Owls Strix occidentalis(Delaney et al. 1999) or wading birds (Black et al.1984). Prior research at Cape Lookout National Sea-shore noted that low-flying aircraft occasionally influ-enced American Oystercatcher incubation behaviour(McGowan & Simons 2006) although this was basedon a very small number of observations. Given timeto habituate, some species of wildlife may adapt tonon-threatening disturbance in their habitat such asaircraft noise.

Conversely, pedestrian activity did alter incuba-tion behaviour. We were unable to assess theeffects of pedestrians on the nesting success ofAmerican Oystercatchers because of small samplesizes. A study at Cumberland Island National Sea-shore, Georgia, found that pedestrians disruptedAmerican Oystercatcher incubation activities andincreased nest failures (Sabine et al. 2006). Pedes-trian activity (researchers checking nests) alsoflushed Eurasian Oystercatchers Haematopusostralegus off their nests, but it did not increaseegg loss (Verboven et al. 2001). Pedestrians mayresemble traditional predators more than othertypes of human disturbance.

In contrast, vehicles were associated withchanges in American Oystercatcher behaviour andnesting success. These ground-based human activi-ties may be perceived as a greater threat by Amer-ican Oystercatchers than more remote air-basedactivities. In particular, ATV activity elicited astrong behavioural response from American Oys-

tercatchers, with Oystercatchers on their nests foronly about 30% of the time ATVs drove past theirnests. This supported the earlier findings of McGo-wan and Simons (2006) that ATV traffic affectedthe incubation behaviour of American Oyster-catchers. Verboven et al. (2001) found that Eura-sian Oystercatchers altered their nesting behaviourin the presence of researchers. The strong responseof American Oystercatchers to ATVs at CapeLookout may reflect an association between ATVsand the activity of researchers, because researchactivities at Cape Lookout are conducted mainlyfrom ATVs. However, it is also likely that smaller,faster and louder ATVs, with more visible humandrivers, appear more threatening to American Oys-tercatchers than other types of vehicle.

Assessing nesting behaviours can provide insightsinto mechanisms underlying effects of disturbanceon nest survival and success. Unattended eggs areprobably more vulnerable to predators (Verbovenet al. 2001), such as ghost crabs (Ocypodinae) andavian predators, and they are subject to temperaturefluctuations that may harm the developing embryo(Robert & Ralph 1975, Anderson & Keith 1980).However, although our comparison of the averagedaily nest attendance for hatched vs. failed nests didsuggest that nest attendance was higher for success-ful nests, the inclusion of other factors in our multi-variate analysis did not show a strong influence ofnest attendance on hatching success. Similarly, wedid not find a relationship between overall humanactivity levels and American Oystercatcher nestattendance. American Oystercatchers may rely ontheir inconspicuous nest scrapes and crypticallycoloured eggs to avoid detection of their nests bypredators (Lee et al. 2010, Colwell et al. 2011), andhigher rates of movement to and from a nest mayattract predators or allow predators to locate nestsmore easily (Martin et al. 2000). Although wefound that American Oystercatchers were often offtheir nests during vehicle and pedestrian events, wefound minimal evidence that human activityaffected the total number of times birds left theirnests in a day, suggesting that they may move toand from their nests frequently during the dayregardless of human activity. Although we foundthat the average number of off-road vehicles drivingby nests per day showed a significant negative corre-lation with nesting success, we did not find a strongcorrelation between the behaviour of incubatingAmerican Oystercatchers and nesting success, sowe cannot identify a clear mechanism to explain



the relationship between vehicle traffic and nestsurvival.

Our analysis of American Oystercatchers in dif-ferent types of vehicle closures was constrained bysmall sample sizes. Furthermore, the location ofnests within closures was not standardized, so thedistance to and visibility of vehicles from nests arelikely to have played a role in the response ofAmerican Oystercatchers. Future research on theeffects of vehicles would benefit from the estab-lishment of complete vehicle closures for the dura-tion of the incubation period, as well as largerclosed areas to decrease visibility of vehicle activitybeyond the boundaries of the closures, to providebehaviour and nest survival rates in completelyundisturbed control sites. A ban on off-road vehi-cles on beaches in South Africa is believed to beresponsible for population and breeding increasesof African Black Oystercatchers (Williams et al.2004).

We were surprised to find a significant positiveassociation between the presence of recordingequipment and daily survival and success of nests.Reproductive success at our video-monitorednests was high compared to average levelsrecorded prior to this study. We observed severalinstances of Raccoons Procyon lotor investigatingvideo cameras without detecting the adjacentAmerican Oystercatcher nests. Most of thesenests survived to hatch successfully. It is possiblethat the recording equipment, being novel fea-tures in the landscape, distracted predators awayfrom nearby nests. Richardson et al. (2009) foundevidence that rates of nest predation were lowerfor avian nests with camera monitoring. The dis-tribution of more nests without recording equip-ment being located in drive-through vehicleclosures and fewer in ramp closures (thereforebeing more frequently in areas of heavier vehicletraffic) as compared to nests with recordingequipment may also have influenced the compar-ative survival and success rates.

The annual reproductive success of AmericanOystercatchers on North Core Banks during thetwo seasons of this study was slightly higher thanthe annual reproductive success reported for theprevious 12 years (Appendix 1) and within therange reported at other sites along the Atlantic coastof the USA (American Oystercatcher WorkingGroup et al. 2012). Although we found an inverserelationship between vehicle numbers and nestingsuccess in our study, we found no evidence of a cor-

relation between annual Park visitation and annualnest survival or productivity from 1998 to 2011.This result contrasts with findings from a study ofAfrican Black Oystercatchers, which found that thenumber of nests, eggs and fledged chicks decreasedas off-road vehicle use and sales increased over timein South Africa (Jeffrey 1987). Annual variation inAmerican Oystercatcher reproductive success ishigh (Fig. 3, Appendix 1, Schulte & Simons 2015)and many factors may affect rates of reproductivesuccess. Most of our research was focused on thenest-incubation period, but the chick-rearing stageis equally important. Schulte (2012) found differ-ences in American Oystercatcher chick behaviourinside and outside of vehicle closures and docu-mented direct mortality of chicks from vehicles.Leseberg et al. (2000) also suggested that vehiclesand human activity may reduce the ability of Afri-can Black Oystercatchers to successfully provisiontheir chicks.

Although our results did not identify a clearmechanism explaining behaviour changes andreduced nesting success associated with human dis-turbance, and the lack of true controls (sites lack-ing any anthropogenic disturbance) constrains ourinterpretations of these results, further insights andseveral clear patterns with implications for conser-vation and management have emerged from thisstudy. American Oystercatchers exhibited humanactivity type-specific responses, suggesting thatmanagement strategies need to be tailored tospecific human activities. Also significant was thefinding that American Oystercatchers were ontheir nests significantly less during off-road vehicleand pedestrian events than they were during con-trol periods before the events, and that increasingnumbers of off-road vehicles passing a nest duringincubation was consistently associated with signifi-cant reductions in nest survival and success, indi-cating that managing pedestrians and vehicles innesting habitats is essential to the conservation ofAmerican Oystercatchers.

Funding was provided by the United States Marine Corps,U.S. Marine Corps Air Station, Cherry Point, NC; wethank Marine Corps personnel including C. Lombardo,D. Plummer, J. Guilianelli, K. Cobb and many others forproviding data and support. Audrey DeRose-Wilson, Mat-thew Hillman, Sarah Karpanty, James Fraser and JessicaStocking were extremely helpful collaborators in thisresearch. We also greatly appreciate Sarah Karpanty’s sug-gestions on the manuscript. Many thanks to J. Wettroth,M. Rikard, J. Altman and the staff of Cape Lookout



National Seashore for project assistance. D. Mennitt, D.Joyce, K. Fristrup and S. Hussain provided software andtechnical support. We are indebted to research assis-tants and volunteers M. Thoemmes, J. Smith, K. Pier-son, M. Peterson, A. Nolker, I. Colon, J. Hampton andM. Fisk. We thank M. Krachey, F. Wu, T. Chen, K.Shusterman, P. Bloomfield, K. Pollock and K. Gross forproviding statistical analysis support. Thanks to N. Had-dad and J. Collazo for project review and advice. Manythanks to R. Nager, M. Frederiksen and two anonymousreviewers for manuscript comments and suggestions.This research was conducted under the auspices of NCState University IACUC protocol #12-046-O. Any useof trade, firm or product names is for descriptive pur-poses only and does not imply endorsement by the U.S.Government.

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Received 8 October 2014;revision accepted 4 February 2016.

Associate Editor: Morten Frederiksen.

APPENDIX 1American Oystercatcher product ivi ty at North Core Banks, Cape Lookout National Seashore, USA, from 1995 to2012

Year andlocation

Breedingpairs Nests

Nestshatched

Nest survivalobserved (se)

Nest survivaladjusted (se)

Chicksfledged

Chicksurvival (se)

Chicks fledged/breeding pair (se)

Cape lookoutNorth Core Banks1998 38 72 5 0.069 (0.030) No data 4 No data 0.105 (0.062)1999 39 61 11 0.177 (0.049) 0.170 (0.042) 5 0.208 (0.083) 0.128 (0.061)2000 29 36 7 0.194 (0.066) 0.248 (0.068) 1 0.059 (0.057) 0.034 (0.034)2001 29 53 12 0.226 (0.057) 0.173 (0.049) 1 0.091 (0.061) 0.034 (0.034)2002 23 46 4 0.087 (0.042) 0.084 (0.033) 5 0.455 (0.150) 0.217 (0.125)2003 20 36 7 0.194 (0.066) 0.157 (0.053) 2 0.118 (0.078) 0.100 (0.069)2004 21 25 20 0.800 (0.080) 0.772 (0.089) 31 0.608 (0.068) 1.476 (0.255)2005 16 20 11 0.550 (0.111) 0.453 (0.120) 6 0.286 (0.099) 0.375 (0.155)2006 14 18 8 0.444 (0.117) 0.399 (0.116) 5 0.263 (0.101) 0.357 (0.133)2007 17 32 8 0.250 (0.077) 0.191 (0.065) 14 0.778 (0.098) 0.824 (0.261)2008 14 22 4 0.182 (0.082) 0.248 (0.084) 3 0.429 (0.187) 0.214 (0.114)2009 29 40 7 0.175 (0.060) 0.188 (0.056) 8 0.533 (0.129) 0.276 (0.121)2010 31 58 15 0.259 (0.059) 0.299 (0.056) 15 0.500 (0.091) 0.484 (0.130)2011 32 54 18 0.333 (0.064) 0.381 (0.061) 24 0.649 (0.078) 0.750 (0.149)2012 15 26 9 0.346 (0.093) 0.351 (0.092) 14 0.636 (0.111) 0.933 (0.284)

Middle Core Banks2004 5 5 4 0.800 (0.179) No data 7 0.875 (0.117) 1.400 (0.510)2005 7 9 5 0.556 (0.166) 0.511 (0.172) 9 0.643 (0.128) 1.286 (0.474)2006 8 9 7 0.778 (0.139 0.745 (0.155) 8 0.500 (0.125) 1.000 (0.267)2007 11 11 7 0.636 (0.145) 0.570 (0.160) 10 0.833 (0.108) 0.909 (0.315)2008 6 6 4 0.667 (0.192) No data 7 0.875 (0.117) 1.167 (0.477)2012 13 18 7 0.389 (0.115) 0.218 (0.106) 12 0.706 (0.111) 0.923 (0.288)

Ophelia Banks2007 2 3 2 0.667 (0.272) No data 3 0.750 (0.217) 1.500 (0.500)2008 2 2 1 0.500 (0.354) No data 0 0.000 (0.000) 0.000 (0.000)

As a consequence of natural barrier island changes and inlet closures and openings, in some years Middle Core Banks and OpheliaBanks may attach and become part of North Core Banks, and in other years they may be separate islands.



http://www.fws.gov/migratorybirds/AboutUS/mbstratplan/finalmbstratplan.pdf

http://www.fws.gov/migratorybirds/AboutUS/mbstratplan/finalmbstratplan.pdf

http://www.fws.gov/migratorybirds/NewReportsPublications/SpecialTopics/BirdsofManagementConcern09%5B1%5D.pdf

http://www.fws.gov/migratorybirds/NewReportsPublications/SpecialTopics/BirdsofManagementConcern09%5B1%5D.pdf

SUPPORTING INFORMATION

Additional Supporting Information may be foundin the online version of this article:

Video S1. A video of an American Oyster-catcher incubating its nest during a low-altitudemilitary aircraft flight through the military opera-tions area (MOA) above North Core Banks, CapeLookout National Seashore, USA. The heartbeatof the incubating adult American Oystercatcher isalso recorded (Borneman et al. 2014) and can beheard throughout the video.

Video S2. A video of the behavioural responseof an incubating American Oystercatcher to an all-terrain vehicle (ATV) driving past its nest at NorthCore Banks, Cape Lookout National Seashore,USA. The heartbeat of the incubating adult Amer-ican Oystercatcher is also recorded (Borneman etal. 2014) and can be heard while the Oyster-catcher is sitting on the nest.



Documents

Off‐road vehicles affect nesting behaviour and ...simons/Borneman_et_al-2016-Ibis.pdf · Off-road vehicles affect nesting behaviour and reproductive success of American Oystercatchers