International Wader Studie A2

DISTURBANCE

TO WATERFOWL

ON ESTUARIES

Edited by Nick Davidson & Phil Rothwell
Wader Study Group Bulletin 68, Special Issue, August 1993


DISTURBANCE
TO
WATERFOWL
ON ESTUARIES

Edited by Nick Davidson & Phil Rothwell

Wader Study Group Bulletin68, Special Issue, August 1993


This publicationcan be obtainedfrom The Royal Societyfor the
Protectionof Birds(The Lodge, Sandy, BedfordshireSG19 2DL, U.K.)
Price ½'15includesp. & p.
This report should be cited as: Disturbance to waterfowlon estuaries
Wader Study Group Bull. 68 Special Issue.

Individualpapersshouldbe cited as: Wader Study GroupBull.68:
These papers have been subjectto peer groupreview.
The statementsmade in individualpapers remainthe intellectualproperty
of the authorsand do not necessarilyrepresentthe views of the editorsor
the sponsoringorganisations.

The editorsacknowledgeBev Whitten, Janice Harnett, Martin Nugent,
Sylvia Sullivan,and all the workshopparticipants,withoutwhom the
meeting and this volume would not have happened.

Copyright¸ 1993 by the Wader StudyGroup(WSG)
Publishedby the RSPB and the Wader Study Group,
w•th financial assistance
Committee

of the U.K. Joint Nature Conservation

Frontcover:by ChrisGomersall(RSPB)

Back cover:by PatrickSutherland(RSPB)

Typesettingby BedfordTypesettersLimited.

Printedby SterlingPress.
ISSN 0260-3799
RSPB

Ref. 22/749/93


Contents
Introduction

Nick Davidson
Wader

and Phil Rothwell

disturbance:

a theoretical

..........................................................................................................................

1

overview

John Cayford .........................................................................................................................................................

3

Effects of disturbance on shorebirds: a summary of existing knowledge from the Dutch Wadden Sea and
Delta

area

Cor Smit and George J. M. Visser .........................................................................................................................

6

Disturbance of foraging knots by aircraft in the Dutch Wadden Sea in August-October 1992
Anita Koolhaas, Anne Dekinga and 'l-heunisPiersma........................................................................................... 20
Experimental wildlife reserves in Denmark: a summary of results
Jesper Madsen ......................................................................................................................................................

23

Studies on the effects of disturbances on staging Brent Geese: a progress report
Martin Stock ...........................................................................................................................................................

The UK Shooting Disturbance Project
Myrfyn Owen ..........................................................................................................................................................

29

35

Some effects of disturbance to waterfowl from bait-digging and wildfowling at Lindisfarne National
Nature Reserve, north-east England
David Townshend

and David O'Connor ................................................................................................................

47

Impact and extent of recreational disturbance to wader roosts on the Dee estuary: some preliminary
results

Jeff Kirby, C Clee and V Seager ............................................................................................................................

53

Disturbance and feeding shorebirds on the Exe estuary
John Goss-Custard

and N Verboven .....................................................................................................................

A preliminary study of the effects of disturbance on feeding Wigeon grazing on Eel-grass Zostera
Tony Fox, D Bell and G Mudge .............................................................................................................................

59

67

Disturbance on estuaries: RSPB nature reserve experience
Graham

Hirons and Gareth

Thomas

.....................................................................................................................

72

Disturbance to estuarine birds: other reports and papers
Nick Davidson

........................................................................................................................................................

79

Kentish Plovers and tourists - competitors on sandy coasts?
Rainer Schulz and Martin Stock ............................................................................................................................

83

The impact of tourism on coastal breeding waders in Western and Southern Europe: an overview
Mike Pienkowski

....................................................................................................................................................

92

Human disturbance to waterfowl on estuaries: conservation and coastal management implications of
current knowledge
Nick Davidson

and Phil Rothwell ...........................................................................................................................

97


Dawdson& Rothwell:Human disturbanceto waterfowlon estuaries:conservationand coastalmanagementimplicationsof currentknowledge

principlesfor coping with potentialrecreationaland
waterfowl demands on estuaries in the future, and

identifyresearch needs.
We concentrate

here on issues of disturbance

to

waterfowlfeeding and roostingon estuarieswhilstthe
birds are on their wintering grounds and during periods
of springand autumn migrations.The effectsand
•mplicationsof recreationaldisturbanceon breeding
waterfowl have rather different patterns of effect and
imphcation(see e.g. Pienkowski1993; Schultz & Stock

1993). They are not consideredfurtherhere although
the overall principleremains the same: people in too
close proximityto birds have at least the potentialfor
creating a disturbingeffect.

explanation). This is because most studies have so far
relied on observationalor semi-experimentalways of
recordingeffects of disturbanceand so cannot readily
be used to deduce the extent of any impact of human
disturbanceon the birds. Conversely,it is just as difficult
to use the available

data to demonstrate

that there is no

impacton waterfowlof a particulardisturbingactivity.
Cayford (1993) suggeststhat future researchcould
concentrateon more experimentalfield manipulations
as a way of controllingfor confoundingvariables.

Coastal research is accustomedto dealing with two

major sets of changingvariables. First is the high
dynamism of coastal systems, as seen throughthe
physical,chemical and biologicalprocessesthat shape
estuaries and open coasts. Second is the
ever-changingpatternof human uses of coastlines,
characterisedby many differentactivitiesoften taking
place simultaneouslybut independently.In studyingthe

However,knowngeneralfeaturesof waterfowlecology
and populationdynamicsdo help by providinga
framework in which to judge disturbanceeffects.
Cayford(1993) pointsout that optimalforagingtheoryis
a useful'basisfrom whichto understandlikelyeffectsof
disturbanceon feeding. Many studieshave shownthat
birds concentratewhere feeding is best (often where
there is best opportunityto maximisenet energy gain). If
birdsare forcedtemporarilyor permanentlyto leave
these places (by disturbance) then there is an increased
risk that their energy balance will suffer. However, the
severity of this type of situationand ways in which birds
respondagain vary in a complex way. Responses
depend on many factors such as whether there are
alternativefeeding areas available. Furthermoresome
parts of a population,e.g. juveniles,can be more

disturbance

affected

STUDYING

AND INTERPRETING

DISTURBANCE

of human activities to birds there is also a

third major set of variables: inter- and intra-specific
d•fferences in the responses shown by birds to even the
same activityat differenttimes and/or in differentplaces
(see e.g. Smit & Visser 1993).
Th•s multiplicityof variables underlyingthe observed
•nteractionsbetween waterfowl and people makes it
d•fficultto assess what is the cause and the implications
of a particular instance of recreationaldisturbance.This
is particularlythe case for observationalstudies.
Althoughthese can identifycorrelationallinksbetween
human disturbance and the responses of the birds it is
often difficultto isolate key variables, and to assess
whether human disturbance adds to or replaces natural
disturbancelevels from e.g. birdsof prey. Furthermore,
the magnitudeof the disturbanceto waterfowlmay arise
from synergisticeffects of more than one activity. For
example Townshend & O'Connor (1993) suggestthat
waterfowl numbers and usage at Lindisfarnein northeast Englandwere affectedby wildfowlingactivity,but
chieflywhen the presence of bait-diggersin just one
part of the area prevented birds from usinga zone
establishedas a non-shot refuge (see also Bell & Fox
(1991) and Owen (1993) for furtherdiscussionof
wildfowlingrefuges).

than others.

Disturbancedoes not in itselfalways implythat it
causes a serious problem to the birds, at least in the
short-term.This is because waterfowlcan compensate
for disruptionsto their natural behaviourpatternsin a
variety of ways. For example some species and
individualsdo not always feed for all the available time
during the tidal cycle. These birds can extend their
periodof feedingto compensatefor time lostduring
disturbance,in a parallel with the extended feeding
times that occurduringperiodsof high energy demand
inducedby cold weather (e.g. Davidson& Evans 1986).
Some waders

can accelerate

food intake rates in

responseto reductionsin time available for feeding
(Swennen et al. 1989). Hence even apparentlyhigh
rates of disturbanceto feeding routinesdo not always
lead to major reductionsin food intake or overall usage
of feedingareas - an example for Oystercatchers
Haematopus ostralegusis describedby Goss-Custard&
Verboven (1993). But note that on the same estuary
there is evidence that another waterfowl species
(WigeonAnas penelope)may be seriouslyaffectedby
even occasionaldisturbance during key parts of the

feeding cycle (Fox et al. 1993), emphasisingthe
difficultyof extrapolatingeven from studiesin the same
location. Care also needs to be taken to ensure that

Measuringand controllingfor the many variablesin
dynamiccoastal systemsis a large task, and one that
may not greatlyhelp in buildinggeneral modelsof
waterfowl use of estuaries with which to compare the
effects of a disturbance(see Cayford 1993 for further

98

conclusionsabout the intensityof disturbanceare not
drawn from only part of the time or area, since
observationscan be concentratedin those placesand
duringthose times when disturbanceis greatest
(Goss-Custard& Verboven 1993).


Davidson& Rothwell:Humandisturbanceto waterfowlon estuaries:conservationand coastalmanagementimplications
of currentknowledge

Comprehensiveunderstandingof the significanceof
disturbance to estuarine waterfowl thus depends on

understandingwhether(and by how much)the birds
have a bufferingcapacityremainingbefore facing
reduced energy balance and so potentiallyreduced
survival.This in turn relies in part on an understanding
of such features as the carryingcapacityof an area, the

nutritionalstate and requirementsof the birds and
actual feeding rates in relationto potentialmaxima.
Since this detailed

information

pressure

is often not available

(and is very hard to establish), assessments must be
based on more limited available

information.

Local
effect

e.g. stop feeding
move within estuary

Another lesson to be learnt from using waterfowl
ecology and population dynamics to underpin
analyses of disturbanceis the need to distinguish
between effect and impact, and between whether it is
individuals or populationsthat are affected. This is
summarised in Figure 1. Many studies, for example
most of those in this volume, report local (i.e. within an
estuary or part of an estuary) effects on at least some
individuals.Examples include cessation of feeding,

changing feeding locationsand moving roostingsites.
In some

cases

there

is evidence

that total numbers

'Estua
effe
e.g.decrease
in
•, estuary
population

'[Estuary
impa
e.g.
birds
die
ct

of

birds using an estuary decreased in response to
human disturbance (Townshend & O'Connor 1993;
Kirby et al. 1993). However, it is much harder to detect

whether such changes have an impact on individual
birds (e.g. by reducingtheir fitness to survive), or on a
waterfowl populationsuch that a biogeographical
population declines. First this is because it is difficult
to control for the many other factors that could affect
fitness and populationdynamics (see Cayford 1993).
Second, waterfowl are highly migratory so that any
effect of disturbance (e.g. leaving on migration in a
poorer nutritionalcondition)could have its impact
many thousandsof kilometresaway e.g. on migratory
staging areas or arctic breedinggrounds(see Evans
et al. 1991; Davidson & Morrison 1992). Large-scale
changes in the use of sites by certain species,
apparently linked to changes in intensityof
disturbance have been noted. Changes in the habits
of species such as Wigeon and Brent Geese Branta
bernicla in response to disturbanceassociated with

Popula
impact

,g,
population
decline•
Figure 1. Stages in detectingeffectsand impactsof disturbanceto
waterfowl.

WHO IS MOST DISTURBED, BY WHOM, WHERE
AND WHEN?

When during the annual cycle?
We have pointedout that human disturbanceon estuaries
adds to a baseline of disturbance from natural causes

suchas birdsof prey or the risingof the tide forcingbirds
to abandonfeedinggrounds.The effectsof such

shootingare well documented(Madsen 1993). Such
changes in habit can be of a scale detectable across

additional disturbance

flyways.

even under natural, undisturbed, conditions, i.e. when

Nevertheless, this volume includesmany examples of
studiesshowingat least localor short-termeffectsof
disturbance, and there is evidence in at least some
cases that such disturbance

can and does lead to a

substantialdecrease in energy balance (e.g. Belanger &
Bedard 1990). Furthermore,despitethe very great
variation in scale and pattern of observed disturbance
responsesthere are some commonfeatures that
emerge whichcan indicatethe locations,times and
circumstancesof highvulnerabilityto disturbance.
These

are discussed

below.

will be most serious at times when

birdshave difficultyfindingsufficientfoodfor their needs
they are at or closeto the thresholdof meetingtheir
energy balance. Such conditionscan arise when either
food is difficultto find and/orwhen demandsfor energy
are high(Pienkowskiet al. 1984). Problemsof balancing
the budgetoccurnotjust when birdsfind difficultyin
meetingtheir daily existenceneeds. Wildfowlaccumulate
storesof fat and proteinin advance of periodsof high
demand.At suchtimesthe dailyfood intakemustgreatly
exceed that needed to supplyshort-termneeds.
There are several circumstancesand times of year
when waterfowlare close to their energy balance

99


Dawdson& RothwelhHuman disturbanceto waterfowlon estuaries:conservationand coastalmanagementimplicationsof currentknowledge
threshold

and so are vulnerable

to additional

disturbance.One is duringperiodsof cold winter
weather.

At such times food becomes

harder to find

whilstenergydemandfor thermoregulationincreases,
so that food intake has to be increased.

When severe

weather lastsfor a few days or more waterfowlregularly
draw on fat and protein stores accumulated earlier in
the winter. Even withoutadditionalproblemscaused by
disturbancesome waterfowl species regularlyhave
increasedmortalityduringcold weather (e.g. Davidson
1981, Davidson & Evans 1982). Such mortalitycan
occur within about one week of the onset of cold

weather. It usuallyseems to occurafter birdshave
exhausted the fat stores that providetheir major energy
source during periodsof insufficientfood intake.
Additional disturbance of waterfowl at such times,

particularlyif it involvesflight, accelerates the rate of
nutrientstore use and so increases mortalityrisks.
Recognitionof this has led since the mid-1980s to the
impositionin the UK and some other European
countriesof statutorybans on wildfowlingduring

prolongedsevere weather, a major objectivebeing to
reduce disturbanceto non-quarryspecies.
In northerntemperate regions most waterfowl
accumulateenergy reservesduringthe early part of the
winter, with a peak in late December - late January
(depending on species) broadly coincidingwith the time
when severe weather

occurs most often. Waterfowl

For waders the periodin autumn when they undergoa
major moult may also be one when the direct and
indirecteffects of disturbanceare high. Moult is a time
when energy demandsare high, because birdsneed to
acquire nutrientsfor the growthof new feathers.
However, as moult takes place at the end of summer
when food is abundant and weather mild, waders

generallyseem to have littledifficultyin meetingenergy
needs. Even so, waders seem to concentrateon large
estuarieswhen moulting,and this is consideredto be an
adaptationto avoidanceof disturbance(Prater 1981).
Certainlyflyingwhen in activewing moultis less
energeticallyefficient,and moultingbirds may be less
manoeuvrableand so more vulnerable to predators.
Hence additionaldisturbancecausingextra periodsof
flightduringmoultwill increasevulnerabilityat this time
of year which is oftenwhen largestnumbersof people
visit estuaries (see below). Some waterfowl become
flightlessduringtheir autumn moult. Such birdsseek

seclusionand are particularlyvulnerableto human
disturbance

that causes them to move from safe

refuges to areas where depredation risk is greater.

are

thereforeparticularlyvulnerableto severe spellsoutside
this midwinterperiod, either in early winter whilst stores
are still being laid down or in late winter/earlyspring
when stores are declining.In early winterfood intake
must exceed daily needs for stores to be accumulated,
so althoughdisturbancemay have no obvious impact at
the time it may delay the timingof energy store gain, so
increasingvulnerabilityto later periodsof severe
weather.

In spring and autumn many waterfowl are gaining large
stores of fat and proteinin preparationfor their major
migrationsbetween Arctic breeding groundsand their
winteringgroundsin Europe and Africa. Duringthese
periodsdaily food requirementsare high and some
evidence indicatesthat birds are feeding at or near their
maximum attainable intake (Ens et al. 1990). These
problemsof achieving high food intakes appear
particularlyacute in springwhen birds are migratingon
very tight schedules so as to reach breeding groundsat
the righttime. Hence in spring(especiallyfrom late April

to late May) disturbancethat reduces net energy gain
could lead to birdsmigratingto their breedinggrounds
with reducedenergy stores. In some years, arctic
wadersneed to draw heavilyon theirstoressoonafter
arrivingon breedinggrounds.If springsnow-meltis late
and weather conditionsare bad, reduced energy stores
may affect breedingsuccessand even adult survival
(see Boyd 1992; Davidson & Morrison 1992). Several
studiesof disturbanceduringmigratorystaginghave

lOO

indeed shown populationeffects includingreductionsin
numbersof birdsusingstagingareas (e.g. Pfisteret al.
1992) and substantialincreasesin daily energy
expenditurethat exceeded the compensatorycapacity
of the birds (Belanger& Bedard 1990).

It is also possible that a disturbance-influenced
redistributionin early autumn may influencebird
distributionlater in autumn and in winter. Knowingabout
such movementsis importantin interpretingeffectsof
disturbance.Observedbirddistributionslater in the year
may reflect the past historyof human disturbance,
especiallyif such redistribution
involvesmovingto a
differentestuary, ratherthan disturbanceobservedat
the time (see also Smit & Visser 1993).
Which species are most vulnerable?
The type and scale of responseby differentwaterfowlto

disturbance is very variable. Even the same species of
bird can react in differentways at differenttimes and on
differentestuaries- for example sometimesby
habituatingto repeated disturbance and at others
becomingincreasinglynervods.For example
Redshanks Tringa totanusfeeding in narrowtidal
creeks with frequentpassers-byon the shore may
tolerate people within20 m, yet Redshankson some
large estuariesfly off when a person is stillover 100 m
away. It is not clear which circumstances lead to
habituationand which to disturbance.Amongstfactors
implicatedin such variabilityare time of year, time of
tide, weather conditions,flock size, feeding success,
type of disturbingagent and past historyof disturbance.

Some general patternsare, however, emerging from all
this variability.Some bird species (e.g. Brent Goose,
Redshank, Bar-tailedGodwit Limosa lapponicaand


Davidson& Rothwell:Human disturbanceto waterfowlon estuaries:conservationand coastalmanagementimplicationsof currentknowledge

Curlew Numenius arquata) are more 'nervous'than
others (e.g. Oystercatcher,TurnstoneArenaria interpres
and Dunlin Calidrisalpina). The presenceof just one
person on a tidal flat can create a surprisinglylarge
cordonsanitairein which birdsstop feeding or fly off, in
one study rangingfrom about 5 ha for gulls and 13 ha
for Dunlinsup to 50 ha for Curlews (Smit & Visser
1993). So a few people evenly scatteredover the tidal

flats can preventbirdsfeeding in a large area of many
estuaries (see below). However, in extreme cases, for
example Wigeon on parts of the Exe Estuary, it can
even be just one disturbanceincidentat the wrong time
that deters birdsfrom feeding untilthe next tidal cycle
(Fox et al. 1993).

What is most disturbing?
There are also general patterns about who and what
causes most serious disturbance
Several

to estuarine

waterfowl.

widespread and long-lastingdisturbance often comes
,'rom aircraft, and that the slower the aircraft the worse

the disturbance- helicopters,microlights,and light
aircraft (even when not low-flying)disturbmore than jets
(Smit & Visser 1993; Stock 1993). Fast (jet) planes also
cause disturbancewhen flying low over feeding grounds
and roosts(Koolhaas et al. 1993) although it is not clear
whether the disturbanceis induced more by the sudden
loud noise or the planes' movement.
On the tidal flats, moving people and animals
(especiallydogs) generallycreate worse disturbance
than people who stay in one place for some time.
However, note that even these static types of use can

cause major disturbanceif they are intensiveand/or
widespread.
From water, close approach to roostingflocks on or
causes serious disturbance.

there too.

On many Britishestuariesmany differenttypes of
recreational activitytake place, so the potential for
synergisticeffects and impacts is considerable. For
example Table 2 shows that out of the 155 British
estuarieshalf or more of 18 categoriesof aquatic-based
recreationoccurredon 52 estuaries (34% of British
estuaries)and that only six estuaries, mostlyin northern
Scotland, had no aquatic recreation recorded. Diverse
aquatic recreationaluse is particularlycommon in
Table 1. The frequenceof occurrenceof some widespread
recreational activities on the British estuarine resource. Data on

the 155 Britishestuaries gives known occurrence in 1989 and

studies have now found that the most

near the shoreline

of the estuaries in Great Britain (Table 1). So birds
movingto a differentestuary as a disturbanceavoidance responseare very likelyto find many
activitiescapable of causingdisturbanceoccurring

In

additionsince for many waders feeding is best on the
tidal flats close to the water's edge, close approachesto
muddyshores both by sailed craft (especially
sail-boards)and high-speedpowered craft create major
disturbancealso to feeding birds. Approachesfrom the
water seem generally to disturbbirds more than from
land: e.g. in one study Curlews flew from a sail-board at
400 m away compared with about 100 m from a walker
(Smit & Visser 1993).

comesfromJNCC's EstuariesReviewdatabasebeing
developedfrom the work of the NCC EstuariesReview
(Davidsonet al. 1991).

Activity

No.

%

75
125
88
66
76
106
132
116
140

44
69

48
81
57
43
49
68
85
75
90
28
45

Golf-courses

47

30

Light aircraftflying

43

28

Power-boating
Sailing
Sail-boarding

Water-skiing
Canoeing
Bathing/generalbeach use
Angling
Walking/dogwalking
Bird-watching
Motor-cycling
Horse-riding

Table 2. Examplesof the diversityof differentaquatic-based
recreational activities on British estuaries. Data on the 155

Britishestuaries gives known occurrence in 1989 and comes

fromJNCC's EstuariesReviewdatabasebeingdevelopedfrom
the workof the NCC EstuariesReview(Davidsonetal. 1991).

Country

Where?

A widespread view of human disturbance to waterfowl
suggeststhat conflictis not a major issue because as
birds are mobile they can readily fly elsewhere to avoid
the disturbance.Ecologicaltheory (see above) shows
that the solutionis not usually so simple. Furthermore,
activitieswith disturbance potential do not occur in
isolationfrom each other, nor in only one place. Surveys

compiledin 1989 by the Nature ConservancyCouncil's

Estuaries Review found, for example, that many
recreationalactivitieswere taking place on half or more

Britishestuaries

Total no.
of

estuaries*

No. with
> 50%

% with
> 50% of

activitytypes activitytypes

England

81

35

43

Scotland
Wales

50

28

6
14

50

155

52

34

Great Britain

12

* total for each countryincludesthose estuariesshared between two
countries,e.g. Severn, Dee, Solway.

101


Dawdson & Rothwell: Human disturbanceto waterfowl on estuaries:conservationand coastal management implicationsof current knowledge

5OO

I

i

I

for feeding will tend to exacerbatesuch disturbance
problemssince some shy species generallyavoid
feedingon narrowshores(e.g. Bryant1979).

I

4OO

Dunlin
ß

No

ß

of

people
300

200

Redshank

100
0

.....
1,000

....•
..••'
2,000

Curlew

•

3,000

4,000

5,000

Area of tidal flats (ha)

F•gure2. The numbersof mobilepeoplewho, if evenlyspaced,would
d•sturbthree differentwader species(Redshank,Curlewand Dunlin)
from different areas of tidal flats, derived from data in Smit & Visser
(1993).

Wales and parts of England,with few Scottishestuaries
beingusedfor morethan eightaquaticactivities.A
similarpatternof multiple-purpose
use of estuaries
occurs for land-based

recreation.

Furthermore

there

tendsto be a greaterdiversityof recreationalactivityon
estuariesthat form part of the Ramsar/SPA networkof
internationallyimportantsites: internationally-important
estuariesaverage 6.7 activities/estuary;
other estuaries
average5.1 activities/estuary.
So in Britainthere is at
least potentialrecreationaldisturbanceto waterfowlin
many places,and from many differentactivitiesin any
one place,withestuariesin Wales and southernand
eastern England having most potentialpressure.
The size of the area available to birds may also affect
levels of disturbance:on small estuaries there may be
few alternative locationsavailable for birds moving away
from a disturbance,and it takes only a few activitiesin
differentplaces to make much of such an area
untenable to birds of some species. A hypothetical
example is shown in Figure 2, which showsthe
cumulative size of a minimum cordon sanitaire created

for differentwader species disturbedby increasing
numbersof mobile people. This impliesthat for some

shy speciessuchas the Curlewas few as 20 evenly

distributedpeople could preventbirdsfrom feeding on
over 1,000 ha of estuary, an area of tidal flats equivalent
to estuaries such as Hamford Water or Southampton
Water. Of course it is highlyunlikelysuch a 'worst-case'
situationwould ever occur, not least since many parts of
the tidal flats of estuaries are too soft for people to move

on them (e.g.Goss-Custard& Verboven1993).
Nevertheless,such figuresdo give an indicationof the
considerablepotentialfor disturbancefrom
intensificationof human activityeven where it involves

quitesmallnumbersof people.Land-claimwhich
narrows the width of intertidal shore available to birds

102

Like the presence of birds on estuaries many
recreationalactivitiesshow marked seasonalityand
many are restrictedto a few of the suite of habitats on
coasts and estuaries. This means there are complex
patternsof both geographicaland temporal overlap
between birds and people. This is illustratedin Figure 3.
Differentwaterfowl are present on estuaries throughout
the year, but their habitat usage differsseasonally. Most
species breed chiefly on the upper parts of sandy
beaches,shingleridgesand saltmarshes,as well as on
coastalgrazing marshesand other grasslands,and
relativelysmall numbersuse tidal flats for feeding. In
contrast,when arctic and boreal breeding populations

return in autumn and early winter they utiliseall habitats
(exceptfor generallylittleuse of maturesand-dunes)for
feedingand for roosting,this usage continuinguntillate
spring(Davidson& Stroudin press).However,many
recreational activities occur chiefly in late summer and
early autumn, leadingto littleoverlapwith periodsof
main bird usage of some habitats.Activitiesthat occur
throughoutthe year, or largelyin winter,can carry a
high riskof causingdisturbance.However,it is probably
the late summer/early autumn period (and sometimes
also in spring)when most recreationalactivitiestake
place, intensityof use is greatest,and waterfowlare
most vulnerable. This period coincideswith the latter
part of the breeding period for local breeders and
particularlywith the arrivaland moultingof the more
northerlybreeding populations.

Interestinglyit seems that sand-dunes(in winter)and
saltmarshes,particularlythose with well developed
creek systems restrictingaccess, may be the habitats
where waterfowl are least vulnerableto anthropogenic
disturbance. Even so there are places where bird use
even of saltmarshesdoes appear to be restrictedby
recreationaluse, for example of parts of the Wadden
Sea by spring-stagingBrentGeese (Stock1993).
However, it is firm, sandy flats, sand beaches and
shingleridgesthat oftenseem to be amongstthe most
widelyand intensivelyused by both peopleand birds,
and where conflictsmay be most common (see e.g.
Pfister eta/. 1992).

InevitablyFigure 3 is a generalisationand masks what
can be major differencesbetween differentestuariesin
the patternof uses and the overlapsof birdsand
people.Suchvariationcan oftenarisethrough
differences of ease of access to the shoreline.

NeverthelessFigure3 does give some pointersto
where conflictof use is most likelyto arise. It also

showsthat some activities,notablylow-flyingby light
aircraftand micro-lights,affectthe wholeestuarine
resourcerather than just some habitats.This, coupled
with the relativelywide-scaleand long-lastingeffectson


Davidson& Rothwell:Human disturbanceto waterfowlon estuaries:conservationand coastalmanagementimplicationsof currentknowledge

Season

Spring

Habitat

Summer Autumn Winter

*

GR SD SB SH SM MF SF SL ()W

A. Birds

Breeding

*

o

*

ß

*

o

o

o

o

*

*

*

*

*

o

*

*

o

*

*

*

*

o

ß

ß

0

ß

ß

ß

ß

ß

Migratory staging

Wintering

B. People
Bathing
Bird-watching
Walking

Bait-digging
Wildfowling

*

Sailing
Sail-boarding

Light
aircraft
flying

ß

ß

0

0

ß

ß

ß

ß

Key:
majorseasons
andhabitatsof use
minor seasons and habitats of use

* Habitattypesare: GR grasslands;
SD sanddunes;SB sandbeaches;
SH shingle;SM saltmarsh;
MF
mudflats;SF sandflats;SL shoreline;OW openwater.
Figure3. Seasonaloccurrenceof birdsand selectedrecreationalactivities,and theirusageof estuarinehabitats.

waterfowlinducedby low-flyingaircraft,place this
activityamongstthe mostcapableof creating
widespreadand seriousdisturbanceto waterfowl.It may
also be amongstthe mostdifficultto controllocally.

without zonation with little or no damaging effects, there

are widespread examples where effects and impacts of
varyingseverityhave been described,despite the
complexityof unravellingsuch multifactorial
phenomena. Clearly people's recreationaland other
uses of estuaries

MANAGING
FOR WATERFOWL
DISTURBING
ACTIVITIES

AND POTENTIALLY

Althoughthere are many instancesin whichwaterfowl
and people appear to co-existon estuarieswith or

can and do lead to disturbance

to

waterfowlwith often uncertainconsequences,so the
guidingprincipleof managingfor human activitiesin
areas that supportimportantwaterfowl populations
needs to be one of avoidanceor limitationof overlap
throughtemporal and Iocationalzoning. Unlike some

103


Davidson& Rothwell:Human disturbanceto waterfowlon estuaries:conservationand coastalmanagementimplicationsof currentknowledge

other estuarine

activities there is often considerable

potentialfor flexibilityin the pursuitof recreationaluses
of estuaries.

The potentialeffects and impactsof disturbancehave
been widely recognisedin wildlifeconservation
legislationand agreements, as has the need to develop
conservationmeasures for birds whilsttaking into
account human uses. For example Article 4.4 of the EC
Directiveon the Conservationof Wild Birds requires
Member States to 'take appropriate steps to avoid ...
any disturbancesaffectingthe birds, in so far as these
wouldbe significanthavingregardto the objectivesof
this Article'.These objectivesare the takingof special
conservationmeasuresconcerningthe habitatof Annex
I species (includingmigratorywatedowl) in order to
ensure their survivaland reproductionin their area of
distribution.In its judgementon the recent LeybuchtBay
(Germany)case the EuropeanCourtfoundthat the
significanceof the disturbancerelated to the level at a
single site rather than at the populationlevel e.g.
involvinga populationdecline.

Other internationalagreementsincludethe recognition
of the need to manage disturbingactivities.The
forthcomingAfrican/Eurasianand Asian/Australasian
Waterfowl Agreements have a series of action plans

which include the need for range states to take
measures

to reduce the levels of disturbance

to

migratorywatedowl caused by human activities
includinghunting,fishingand other outdoorrecreation.
The actionplans identifyappropriatemeasuressuch as
the establishment of disturbance-free zones in protected
areas where no human access is permitted, and the
establishmentof core sanctuaryareas withinmajor
watedowl huntingareas (IWRB 1993). International
conservationplans for individualwatedowl species
currentlyunderdevelopmentalso recognisethe
impodanceof managingfor recreationaland other
disturbance(e.g. Stroud in press). They also identifythe
need for informationon the pattern and distributionof
potentiallydisturbingactivitiesand populationson a
watedowl flyway scale, usingcompatiblemethodologies
(Davidson et al. 1991; in press).
Organisationsinvolvedin developingstrategiesfor
coastal and estuarine conservation

FUTURE

There has already been considerablework on the
integrationof recreationwith other estuarine uses, and

and other estuarine

wildlife.

DIRECTIONS

Continuingto developways of integratingthe many
different recreational uses on an estuary, both with each
other and with migratorywatedowl populationsso as to
avoid continuingor increasingpressureon this
internationallyimportantpart of our wildlifeheritageis
one of the keysto achievingsuccessfulintegrated
coastalzone management.The impodanceof achieving
such integrationis increasinglyrecognisedas an
essentialplank in establishingsustainableuse of
estuaries for the future. Such integrationcan be
achieved in a variety of ways: througheducationand
the provisionof information,and throughvoluntaryand
statutoryagreements and zonations.

Implementingthe best approachto minimising
disturbanceto watedowl in each locationdependson a
good understandingof the behaviour and needs of both
birds and people. Otherwise there are risksof
exacerbatingratherthan reducinga problem,for
example by establishingzones in incorrectplaces in
relationto bird usage. However, for the reasonswe
have describedabove such informationis not always
available nor easy to acquire. A recent workshop
(Doody 1993) has identifiedkey topics requiringfurther

research on coastal recreation

in the UK. These include:

ß reviewingof currentliteratureand researchon the
relationshipbetween ecologicaland recreational

within Great Britain

also recogniserecreationaland other disturbanceto
watedowlas a key issuethat needs addressingin the
preparationof integratedcoastal zone management
(e.g. Rothwell& Housden 1990; EnglishNature 1992).
EnglishNature'sinitiativefor the promotionof estuary
managementplans based on sustainableestuarineuse
includesobjectivesaimed at identifyingand resolving
multi-useconflictsso as to avoid damage to estuarine
wildlife(Grabrovaz1993).

104

with the needs of waterfowl

There are numerousexamples of the developmentof
refuge areas and use of zonation (both temporal and
Iocational),especiallyin relationto wildfowling(e.g.
Hirons & Thomas 1993; Madsen 1993; Owen 1993;
Townshend& O'Connor1993) as well as attemptsto
manage more general leisure and recreationalusage
(e.g. Kirbyet al. 1993). In addition,types of conflict

between individualsports and nature conservationhave
been assessed by Sidaway (1988) and good practice
examples of coastal recreationmanagement,including
those aimed specificallyat reducingdisturbanceto
waterfowl,are beingwidelypublicised(e.g. Sports
Council 1992).

issues;

ß establishingstandardisedmethodsfor assessing
recreational impact;
ß experimentalwork on habitat and speciesfeatures
to establishwhen changes occur in relationto the
level and timingof activityand in relationto zoning;
ß reviewingpeople's attitudesto recreational
disturbanceof ecologicalfeatures; and
ß assessingthe vulnerabilityof habitats,speciesand
sites in relation to recreational

These

recommendations

uses.

for research

on broader

recreational issues than just disturbanceto watedowl

Davidson& Rothwell:Humandisturbance
to waterfowlon estuaries:conservation
andcoastalmanagementimplications
of currentknowledge

link closely with Cayford's (1993) view that much of the
future research should be experimental. Much of the
research on the topics listed by Doody (1993) would
contributevaluably to our understandingof how
disturbance

affects waterfowl.

in order to understand

Coastal

Marine

Science 9: 369-385.

Burd,F. 1992. Erosionand vegetationalchangeon saltmarshesof
Essex and north Kent between

This current volume

helps to increase the availabilityand variety of the
existinginformationbase. In doing so it clearly reveals

the need for further research

Bryant,D.M. 1979. Effectsof prey densityand site characteristicson
estuary usage by overwinteringwaders (Charadrii).Estuanne &

the

ways in which a wide variety of factors influencethe
extent, effect and impactof disturbanceto estuarine
waterfowl.

1973 and 1988. Research &

surveyin natureconservationNo. 42. Nature Conservancy
Council, Peterborough.
Cayford, J. 1993. Wader disturbance:a theoretical overview. Wader
Study Group Buff.68 (Special Issue).

Davidson,N.C. 1981. Survivalof shorebirds(Charadrii)duringsevere
weather: the role of nutritionalreserves. Pp. 231-249 in N.V

Jones& W.J. Wolff(eds.),Feedingand survivalstrategiesof

Additionally,we believe that much more effort is
requiredto achieve an understandingof fluctuationsin

populationsizes of speciessite by site, regionby region
and flyway by flyway. The opportunitiesto examine
impactsof permanenthabitat losscaused by
developmentor coastalsqueeze shouldbe exploited.

They could tell us much about the behaviourof
individualsand populationsin responseto major
perturbations.We would also encouragethe increasein
the use of major experimentationon populations.The
massive impactson distributionand populationsize
caused by removingor imposingreserve statusor on
the commencementor cessationof a disturbingactivity
such as shooting,mud walkingor militaryuse deserves
greater attention. Such work has to be on a truly
internationalscale. Only by examiningthe full
geographicalrange of a species and the factors
influencingits distributionand survivalwill we be able to
begin to answer some of the questionssurrounding
sustainabilityand maintenanceof biodiversity.

to waterfowl.

1 and 2.

REFERENCES
Belanger, L. & Bedard, J. 1990. Energeticcost of man-induced
disturbance to stagingSnow Geese. J. Wildl.Management 54:
36-41.

Bell, D.V. & Fox, A.D. 1991. Shootingdisturbance:an assessment
of its impact and effects on overwinteringwaterfowl
populationsand their distributionin the United Kingdom.
Report to Nature Conservancy Council by Wildfowl &
Wetlands Trust and BritishAssociationfor Shooting&
Conservation.

Boyd, H. 1992. Arcticsummerconditionsand BritishKnot numbers:
an exploratoryanalysis. Wader Study GroupBuff.64, Suppl.:
144-152.

man-made

and man-modified

wetlands in the enhancement

of

the survivalof overwinteringshorebirds.Colonial Waterbirds9'
176-188.

Davidson,N.C., Laffoley,D. d'A., Doody,J.P., Way, L.S., Gordon,J,
Key, R., Drake, C.M., Pienkowski,M.W., Mitchell, R. & Duff,
K.L. 1991. Nature conservation and estuaries in Great Britain

Nature ConservancyCouncil,Peterborough.

Davidson,N.C. & Morrison,R.I.G. 1992.Time-budgetsof prebreedingKnotson EllesmereIsland,Canada. WaderStudy
Group Buff.64, Suppl.: 137-143.

Davidson,N.C. & Rothwell,P.I. (eds.) 1993. Disturbanceto waterfowl
on estuaries.Wader StudyGroupBuff.68 (Special Issue).

Davidson,N.C., Rothwell,P.I. & Pienkowski,M.W. In press.Towards
a flywayconservationstrategyfor waders. Proc. 1992 WSG

Odessa Conference.Wader StudyGroupBuff.,Special Issue.

Greece, April 1993.

Doody,J.P. 1993. Workshopon "Coastalrecreationecologyresearch
needs". Coastal News 2/93: in press.

We thank also

David Stroudand Ken Norrisfor providinginformation
and helpfulcommentson earlier versionsof this paper,
and AphroditeNiggebruggefor preparingthe data used
in Tables

Davidson,N.C. & Evans,P.R. 1986. The roleand potentialof

conservation:
conservingcoastalhabitatnetworkson migratory
waterfowlflyways.Proc.4th EUCC Congress,Marathon,

The synthesisin this paper could not have been made
withoutthe contributionsto the presentationsand
discussionsat the originalNCC/RSPB workshopon
disturbance

Davidson,N.C. & Evans, P.R. 1982. Mortalityof Redshanksand
Oystercatchersfrom starvationduringsevere weather. Bird
Study 29: 183-189.

Davidson, N.C. & Stroud, D.A. in press. Internationalcoastal

ACKNOWLEDGEMENTS

recreational

estuarineorganisms.Plenum Press, New York.

EnglishNature. 1992. Caringfor England'sestuaries.An agenda for
action. EnglishNature, Peterborough.

Ens, B.J., Piersma,T., Wolff,W.J. & Zwarts,L. (eds.) 1990.
Homewardbound:problemswadersface when migratingfrom
the Bancd'Arguin,Mauritania,to theirnorthernbreeding
groundsin spring.Ardea 78(1/2).
Evans, P.R., Davidson, N.C., Piersma, T. & Pienkowski, M.W. 1991.

Implicationsof habitatlossat migrationstagingpostsfor
shorebirdpopulations.Acta XX Int. Orn. Congr.:2228-2235

Fox, A.D., Bell, D.V. & Mudge,G.P. 1993. A preliminarystudyof the
effectsof disturbanceon feedingWigeon grazingon
Eel-grassZostera. Wader StudyGroupBull.68 (Special
Issue).

Grabrovaz,M. 1993. Strategyfor the sustainableuse of England's
estuaries.ConsultationDocument.EnglishNature,
Peterborough.

Goss-Custard,
J.D. & Verboven,N. 1993. Disturbance

andfeeding
shorebirdson the Exe estuary.WaderStudyGroupBull.68
(Special Issue).

105


Dawdson & Rothwell: Human disturbanceto waterfowl on estuaries:conservationand coastal management implicationsof current knowledge
H•rons, G. & Thomas, G. 1993. Disturbance on estuaries: RSPB
nature reserve experience. Wader Study Group Buff.68
(Special Issue).
International Waterfowl & Wetlands Research Bureau. 1993. The

African/Eurasian WaterfowlAgreement and the
Asian/AustralasianWaterfowlAgreement.Two Agreements
under the Bonn Convention. Action Plans, Proposed Structure.
IWRB, Slimbridge.

K•rby,J.S., Clee, C. & Seager, V. 1993. Impactand extentof
recreationaldisturbanceto wader roostson the Dee estuary:
some preliminaryresults. WaderStudyGroupBuff.68 (Special
Issue).
Koolhaas,A., Dekinga,A. & Piersma,T. 1993. Disturbanceof foraging
Knotsby aircraftin the DutchWadden Sea in August-October
1992. Wader Study Group Buff.68 (Special Issue).
Madsen, J. 1993. Experimentalwildlifereservesin Denmark:a
summaryof results.WaderStudyGroupBuff.68 (SpecialIssue).

Prater, A.J. 1981. Estuary birds of Britain and Ireland. T. & A.D.
Poyser, Berkhamsted.

Rothwell, P.I. & Housden, S.D. 1990. Turning the Tide. A Future for
Estuaries.The Royal Society for the Protectionof Birds,
Sandy.
Schultz, R. & Stock, M. 1993. Kentish Plovers and tourists:competitors
on sandycoasts?WaderStudy GroupBuff.68 (SpecialIssue).

Sidaway, R. 1988. Sport, recreationand nature conservation.Sports
Council and Countryside Commission, London.
Smit, C. J. & Visser, G.J.M. 1993. Effects of disturbance on

shorebirds:a summaryof existingknowledgefrom the Dutch
Wadden Sea and Delta area. Wader Study Group Buff.68
(Special Issue).
Sports Council 1992. Heritage Coasts.Good practicein the Planning,
Managementand SustainableDevelopmentof Sportand Active
Recreation. Factfile 3 Countrysideand Water Recreation.
Sports Council, London.

Owen, M. 1993. The UK shootingdisturbanceproject.Wader Study
Group Buff.68 (Special Issue).

Pfister,C., Harrington,B.A. & Levine,M. 1992. The impactof human
disturbanceon shorebirdsat a migrationstagingarea. Biol.
Cons. 60:115-126.

P•enkowski, M.W., Ferns, P.N., Davidson, N.C. & Worrall, D.H.

1984. Balancingthe budget:measuringthe energyintakeand
requirementsof shorebirdsin the field. Pp. 29-56 in P.R.

Evans, J.D. Goss-Custard& W.G. Hale (eds.), Coastal waders
and wildfowlin winter. Cambridge University Press,

Stock, M. 1993. Studies on the effects of disturbanceson staging

Brent Geese: a progressreport. Wader Study GroupBuff.68
(Special Issue).
Stroud, D.A. in press. The developmentof an international
conservationplan for the Greenland White-frontedGoose.
IWRB Special Publ.
Swennen, C., Leopold, M.F. & de Bruijn, L.LM. 1989. Time-stressed
oystercatchers,Haematopusostralegus,can increaseintake
rate. Anim. Behav.

38: 8-22.

Cambridge.
Townshend, D.J. & O'Connor, D.A. 1993. Some effects of disturbance

P•enkowski,M.W. 1993. The impactof tourismon coastal breeding
waders in western and southernEurope:an overview. Wader
Study Group Buff.68 (Special Issue).

to waterfowlfrom bait-diggingand wildfowlingat Lindisfarne
National Nature Reserve, north-east England. Wader Study
Group Buff.68 (Special Issue).

* 'Effects'and 'impact'are usedin the biologicalsense:i.e. effect=observed
response;impact=implies
reductionin survivalat individual

or
populationlevel.

106