Integrating Marine and Terrestrial Habitats in Shorebird Conservation Planning

Integrating marine and terrestrial habitats in shorebird conservation planning

PHILIPPAC.F. SHEPHERD*#, LESLEY J. EVANS OGDEN + & DAVID B. LANK

Centre for WildlifeEcology, Department of BiologicalSciences, Simon Fraser University,8888 UniversityDrive, Bumaby, BritishColumbia, Canada, V5A lS6, e-marl:Pippa. Shepherd@pc. gc. ca

Shepherd,P.C.F., EvansOgden, L.J. & Lank, D.B. 2003. Integratingmarine and terrestrialhabitats in shorebirdconservationplanning. Wader Study Group Bull. 100: 40-42.

Our studiesin the FraserRiver Delta, British Columbia,Canada, show that shorebirdsthat normallyfeed in the intertidal zone by day make greateruse of terrestrialhabitats for foragingthan had previouslybeen supposed,especially at night.We highlightthe importanceof shorebirdecologists extending their studiesto evaluatefully theuse of non-marinehabitats and the significanceof night-feeding.We outlinethe techniques that can be usedto monitor habitatuse and foraging strategieson a 24-hour day basis.We alsodraw atten- tion to the importanceof passingthe resultsof suchstudies to land-useplanners so that they caninclude key terrestrialhabitats in managementplans for coastalwetland sites.

INTRODUCTION lationsby incorporatingadjacent terrestrial habitats in addi- tionto intertidalmarine and wetland habitats. The availability Many shorebirdspecies are at risk asa resultof theirreliance of intertidalforaging habitats varies with the tidal cycle,and on coastal habitats that are also favoured for human settle- birdsmay be completelyexcluded from certainsites during ment. More than half of the coastalwetlands in the contigu- high tides. Where suitable adjacenthabitat exists, some ous United States have been lost or altered since the arrival shorebirdspecies move from intertidal areas to feed in of Europeansettlers, and in the last centuryalone, an esti- nearbyfields as high tides,lower temperatures,and rainfall mated 70% of California's coastal wetlands have been lost reducethe profitabilityof foragingat intertidalsites (Goss- to development(National WetlandsWorking Group 1988, Custard1969, Kelly & Cogswell 1979, Pageet al. 1979, Bildstein et al. 1991, NOAA 2001, Speth 1979). Represent- Townshend 1981, Rottenborn 1996, Colwell & Dodd 1997, ingjust 17% of the land areaof theUS, coastalcounties sup- Butler 1999, Shepherdet al. 2001). Shorebirdsmay alsouse port over half the US humanpopulation, and population differentforaging habitats by day andby night(Robert et al. growthin theseareas exceeds the nationalaverage (Culliton 1989, Mouritsen 1994, Dodd & Colwell 1998, Sitters et al. 1998). Not surprisingly,coastal habitat alteration is occur- 2001). ring at an alarmingrate. Declinesin manyNorth Americanshorebird species have SHOREBIRD FORAGING STRATEGIES IN THE been attributed to the loss of coastal wetland habitats, and FRASER RIVER DELTA their conservation has been identified as one of the main strategiesfor reversingdeclines and stabilizingpopulations We investigatedhabitat preferences, foraging activity budg- (Donaldsonet al. 2001, Brown et al. 2001). Becauseshore- etsand diet compositionof Dunlin Calidrisalpina pacifica birdshave relatively low reproductivepotential, their popu- in the Fraser River Delta, British Columbia, the northernmost lationsare particularlysensitive to factorsaffecting adult sitein North Americato supporta large non-breedingpopu- survivorship(Hitchcock & Gratto-Trevor1997, Sandercock, lation(numbering 30-60 thousandindividuals) (Warnock & this volume).Most adultmortality takes place during migra- Gill 1996, Shepherd2001a). The FraserDelta is the largest tion or on thewintering grounds where shorebirds often con- wetlandon Canada'sPacific coast and supports the country's centrate in large numbers at relatively few key coastal highestdensities of waterbirds,raptors and shorebirdsin wetlandsites (Myers et al. 1987,Evans 1991). This tendency winter (Butler & Campbell 1987). It is also a key stopover to concentratein spaceand time "breaksthe normal link sitefor migratoryspecies flying betweenbreeding habitats betweenthe abundanceof a speciesand its immunity to ex- in Canada,Alaska and Russiaand non-breedinghabitats in tinction" (p. 21, Myers et al. 1987). southern USA and Central and South America. Over two Conservationand restorationplans for key coastalwet- million shorebirdsuse the Delta annually,including interna- land sitesmay providefurther benefits to shorebirdpopu- tionallyimportant populations of Dunlin andWestern Sand-

* Correspondingauthor #Presentaddress: Ecosystem Services, Western Canada Service Centre, Parks Canada, 300-300 W. GeorgiaStreet, Vancouver, British Columbia, Canada, V6B 6B4 * Presentaddress: Centre for AppliedConservation Research, 3rd Floor, Forest Sciences Centre, 2424 Main Mall, Univer- sity of British Columbia,Vancouver, British Columbia,Canada, V6T 1Z4

Bulletin 100 April 2003 40 Shepherd et al.: Integrabngmanne and terrestnal habitats 41 pipers Calidris mauri (Butler & Vermeer 1994). The land ers and stewards, we needed to determine which habitats surroundingthe Delta supportsa variety of agriculturaluses were preferredby Dunlin and to quantifytheir relative im- and suburbanhousing, and is an areaof increasinglydense portance.Dunlin showeda significantand consistentover- human settlement. all preferencefor foragingin marineintertidal habitats over We usedradio telemetry and direct observation to inves- terrestrialhabitats. However, the majorityof the wintering tigateDunlin habitat preferences and activity budgets in both populationalso foraged terrestrially (Shepherd 200lb, Evans marineand terrestrial habitats, and stable isotope analyses to Ogden2002). Within the terrestrialzone, Dunlin preferred determine the relative contribution of marine and terrestrial soil-basedagricultural habitats with shortvegetation (includ- food to the Dunlin diet (Shepherd200lb, Evans Ogden ing pastures,bare fields with below-groundcrop remains, 2002). Shorebirdswintering in temperateestuaries are gen- fieldswith above-and below-ground crop remains, and win- erally activeboth day and night (Mouritsen 1994, Warnock ter covercrops) over other terrestrial habitats (including sub- & Takekawa 1996). In order to avoid obtainingbiased or urban areas,greenhouse areas, tall grasses,wooded areas, incompleteresults, we thereforecollected data throughout turf, andnursery crops) (Shepherd 200 lb). Of the soil-based the 24-hourday andtwice-daily tidal cycles.We foundthat agriculturalhabitats, pasture, which is heavilyand naturally individualDunlin spentsimilar proportions of time foraging fertilized with cattle manure in the Fraser Delta, was the most day and night, and that use of available habitats differed preferred. between day and night (Shepherd200lb). Our research At the FraserRiver Delta, the northernend of the Dunlin' s showed that more than 70% of radio-marked individuals corewinter range, access to nearbyterrestrial habitats may usedterrestrial habitats adjacent to the intertidal zone, that berequired by manyindividuals in orderto meetdaily energy Dunlinlocated in terrestrialhabitats used them primarily for requirements(Davidson & Evans 1986, Shepherd200lb, foraging(on averagemore than 60% of the time spentthere), Evans Ogden 2002). However, without behavioural data and that terrestrialfood itemsmade up an averageof about collectedat night, or stableisotope data showingrelative 30% of the Dunlin diet (determinedby stapleisotope analy- proportionsof marine and terrestrialfoods in the diet over sis) (Shepherd200 lb, EvansOgden 2002). Interestingly,we thewinter period, we wouldnot have understood the impor- foundthat useof terrestrialforaging habitats was primarily tanceof maintainingsoil-based agricultural habitats adjacent nocturnal.We hypothesizedthat this wasbecause predation to intertidalhabitats. Other studies support the contention that risk and human-related disturbance in the terrestrial habitats alternativehigh tide foraging habitats, in particularsoil-based were lower at night than duringthe day, sinceboth humans agriculturalfields, can be importantfor winteringshorebird andthe Dunlins' primary predators (falcons) are mostly only populations(Velasquez and Hockey 1991, Colwell & Dodd activeby day. Wilson's PloversCharadrius wilsonia cin- 1995, Wamock & Takekawa 1996, Rottenborn 1996, Weber namominuswintering in Venezuela switchedto foraging & Haig 1996, Butler 1999, Dann 1999, Masero & Perez- primarilyat nightapparently due to an increasein the risk of Hurtado2001, Smart& Gill 2003). Predictedmortality rates predationduring the months that their diurnal predators (Per- of EurasianOystercatchers Haematopus ostralegus winter- egrinesFalco peregrinus) were present (Thibault & McNeil ing in Britain in an environmentsimilar to that of the Fraser 1994). Delta increasedsignificantly when upshore and field forag- Becausealternative terrestrial foraging habitats were pri- ing areaswere removedfrom a populationmodel (Stillman marily usedat night,their valueto Dunlin had previously et al. 2000). been underestimatedand the conservationrequirements of The use of soil-basedagricultural habitats as alternative shorebirdshad not been incorporatedinto local land-use foraging sites is not limited to shorebirds. Lovvorn & planningprocesses. Avian managementplans for terrestrial Baldwin (1996) foundthat intertidalhabitats with adjacent habitatsin the FraserDelta regionhad focusedon the needs farmlandsupported 75-94% of individualsof four waterfowl of raptors,passefines, and waterfowl;birds whoserequire- specieswintering in thePuget Sound region (just south of the ments can differ from those of shorebirds.For example, FraserDelta), and foundthat few locationswith no adjacent raptormanagement zones consist of areascovered with tall farmlandsupported significant waterfowl populations. The grassesand other vegetation with man-madeperches, places presenceof grazingwaterfowl can alsofacilitate subsequent that shorebirdstend to avoid. Hedgerowsare promotedas agriculturalhabitat use by shorebirdspecies, such as Dunlin, habitat for passefines,but the resultingfragmentation of that prefer shortvegetation. In the FraserDelta, winter field fields and additionof perchingand hiding sitesfor raptors vegetationcan grow quitetall, therebyrestricting access to may be detrimentalto shorebirds.Until recently,freshwater soil invertebratesand obscuringthe view of approaching wetlandsin theregion were managed exclusively for water- predators.Waterfowl convert the fieldsby grazinginto more fowl andkept at waterlevels that largely excluded foraging shorebird-favourablehabitat, and shorebirdsin the region shorebirds. havebeen observed to makegreater use of agriculturalhabi- Shorebirdspecies that usealternative foraging habitats, tatsafter the winteringwaterfowl have grazed back the veg- particularlyin terrestrialareas with humanactivity, provide etation(Taitt 1997, EvansOgden 2002). an interestingchallenge to managersby requiringan ap- proachto conservationand land-use planning that integrates CONCLUSIONS marineintertidal and adjacent terrestrial habitats, and implies the needfor a managementregime more complexthan just We contendthat shorebirdecologists working at non-breed- habitatprotection. Farmland can be managedand worked in ing coastalwetland sites, particularly at timesor in places ways that are compatibleor incompatiblewith shorebird whereenergetic costs are high such as periods of pre-migra- usage, and successfulconservation plans will hinge on tory fatteningor placeswhere temperatures are low, should farmer support,cooperation, and willingnessto engagein takeinto accountthe birds' requirementsthroughout the full stewardshipactivities. 24-hour day and whole tidal cycles.Such data can be col- In orderto providecomprehensive advice to landmanag- lectedby observation(with the assistanceof modernnight

Bulletin 100 April 2003 42 Wader Study Group Bulletin vision equipment),by radar,by radio telemetry,or by stable Lovvorn, J.R. & Baldwin, K.R. 1996. Intertidal and farmland habitats isotope analysisto provide a more completepicture of of ducks in the Puget Sound region: a landscapeperspecitve. Biol. Cons. 77: 97-114. shorebirdrequirements. It is also essentialthat researchers Masero, J.A.& Perez-Hurtado, A. 2001. Importanceof the supratidal investigatethe useof alternativehigh tide foraginghabitats, habitatsfor maintainingoverwintering shorebird populations: how particularlysoil-based agricultural lands, and the relative redshanksuse tidal mudflatsand adjacentsaltworks in southernEur- importanceof thesehabitats to the birds.Where research ope. Condor 103: 21-30. findingsindicate significant value of suchhabitats, we en- Mouritsen, K.N. 1994. 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