Wader Populations Are Declining &Hyphen; How Will We Elucidate The
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Wader populations are declining - how will we elucidate the reasons? CHRISTOPHZOCKLER '1, SIMON DELANY2 & WARD HAGEMEIJER2 1UNEP-WCMC,219 HuntingdonRoad, Cambridge, U.K., e-mail: Christoph. Zockler@unep-wcmc. org; 2WetlandsInternational, PO Box471, 6700 AL Wageningen,The Netherlands Z6ckler, C., Delany, S. & Hagemeijer,W. 2003. Wader populationsare declining - how will we elucidatethe reasons?Wader Study Group Bull. 100: 202-211. Worldwide,many waderpopulations have beenshown to be in decline,though for someinformation is still lacking.Not all populationsare declining, but long-distance migrants (a majority)appear to be at particular risk. Also at risk are sedentaryspecies with smallpopulations, which comprise a majorityof the extinctand globallythreatened species. The latter are betterstudied, and threats to their futureare relativelywell under- stood.Large-scale population changes in Arcticand north-temperate regions are generally better documented thanin the tropicsor the SouthernHemisphere. The reasonsfor declinesin largeand widespread populations are not well understoodand explanationsare mostlybased on sparseand uncoordinated data. The InternationalWaterbird Census (IWC), coordinatedby WetlandsInternational, provides a framework for monitoringnon-breeding populations at a globalscale. However, wader counts are not yet availablefrom mostcountries for enoughyears to allow meaningfulpopulation trend analyses. Nevertheless there is con- siderablepotential for trendanalyses using IWC data in the future.Many otherstudies use different and un- coordinatedmethods. We still lack facilities for broad-scaleanalyses which would allow the reasonsfor observedchanges in waderpopulations to be explored.A GIS referenced,decentralised, web-based database interfaceis proposedwhich would help explainthese changes by linkingwader monitoring initiatives, and by providingintegration with otherenvironmental monitoring schemes. EXISTING KNOWLEDGE OF POPULATION STATUS Global assessmentsproduced every three to five yearsby Wetlands International estimate the numbers and summarise Global approaches the statusof waterbirdpopulations, but alsodemonstrate the gapsin our knowledge(Rose & Scott 1994, Rose & Scott Wetlands Internationalhas been publishingresults of the 1997, Wetlands International2002). Wetlands International IWC and trendsin certainwaterbird populations for many (2002) compiledestimates of numbersand trendsfor 499 years(Atkinson Willes 1976, 1978, 1981, RQgeret al. 1986, populationsof 209 speciesrecognised as "waders".Table 1 van der Ven 1987, 1988, Monval & Pirot 1989, Scott & Rose summarisesthe numberof speciesin eachwader family, the 1989, Perennou et al. 1990, Perennou, 1991, 1992, Perennou numberof biogeographicpopulations into whichthese fami- & Mundkur 1991, 1992, Rose 1992, Mundkur & Taylor lies have beendivided, the numberof populationestimates 1993, Taylor & Rose 1994, Rose 1995, Dodman& Taylor andtrends presented for eachfamily, andthe number of these 1995, 1996, Lopez & Mundkur 1997, Dodmanet al. 1997, trendswhich were estimatedto be increasing,stable, or de- 1998, Delany et al. 1999, Blanco& Carbonell2001, Gilissen creasing.Seven populations which have becomeextinct et al. 2002). This work hasprovided important baseline in- since 1750 are also included. formationabout waterbird numbers, and successfulpopula- Populationestimates are now availablefor a majority tion trend analysishas been possiblefor certain groups, (424, 85%) of waderpopulations (Table 1). The numberof notablyAnatidae in Europe.The censusresults (and hence populationsfor which the trend is now known is abouthalf the IWC data)are incomplete for certainsites, species or re- of this(207, 41%). Of thepopulations with knowntrends, 92 gions.Because of thesegaps, methodological inconsistencies (44%) showa decreasingtrend, 81 (39%) appearto be stable and otherconstraints, trend data are still lackingfor many and only 27 (13%) show an increasingtrend. The baseline populations.Significant efforts are being made at presentto of availablepopulation estimates continues to grow,and we improvethis situation.Waders have only beenincluded in alsoexpect the quantityand quality of populationtrend data IWC in mostcountries for the mostrecent 10 or so yearsof to showimprovements in the comingyears. These improve- its 35-year history, and no wader data are included in the mentswill includean increase in thenumber of waderspecies IWC databasefor years before 1989. Information about for which sufficientdata are availablefor trendanalysis to populationtrends in wadersis thusonly now becoming avail- be meaningful.An expectedincrease in coverageby IWC, able, althoughprospects for future trendanalyses for wad- andthe developmentof monitoringof ImportantBird Areas ers basedon IWC data are very good. (IBAs) underBirdLife International'sIBA programme,will * Correspondingauthor • Bufietin100April2003 202 ZOckler et aL: Wader populations are declining 203 Table 1, Summaryof data presentedfor waders in Waterbird PopulationEstimates - third edition (Wetlands International2002). Family No of No of bio- No of No. of species geographic population population populations estimates trends presented 'presented Details of presented trends Increasing Stable Decreasing Extinct RostratulidaePainted snipes 2 4 2 1 0 0 1 Dromadididae Crab plovers 1 1 1 1 0 1 0 HaematopodidaeOystercatchers 12 20 20 9 5 3 0 IbidorhynchidaeIbisbill 1 1 0 0 0 0 0 Recurvirostridae Stilts & Avocets 10 25 23 14 4 9 1 Burhinidae Thick-knees 9 25 14 5 0 0 5 Glareolidae Coursers,Pratincoles 17 46 33 12 0 6 6 Charadriidae Plovers & allies 67 156 134 59 11 19 28 ScolopacidaeSnipes, Sandpipers, 90 221 197 106 7 43 51 Phalaropes& allies Total 209 499 424 207 27 81 92 7 % of populations 85% 41% 13% 39% 44% 4% alsobe significantin this respect.The challengewill be to temperate Europe and reduced numbers have also been effectivelycombine and present the resultsof numerousand foundon winteringgrounds in West Africa. However, data diverse studiesat a number of scalesin a meaningful and from the Arctic arecurrently too sparseto concludethat there accessible manner. hasbeen an overalldecline in the populationof this still very abundantspecies (Z6ckler 2002). Europe The Americas A major analysisof wadertrends in the WesternPalearctic, usingIWC data, is planned,and a preliminaryanalysis for Considerableeffort is put into shorebirdconservation in one species,the EurasianOystercatcher Haematopus ostra- North America,and comprehensive conservation plans have leguswas presentedin February2002 (Haanstrain prep). beenprepared for the USA (Brown et al. 2000) and Canada BirdLife International/EuropeanBird CensusCouncil (Donaldsonet al. 2000). Morrison et al. (2001) presented (2000) reportedthat about24 of the 42 wader populations populationestimates and trends for North Americabased on breedingin Europeshowed a decreasingtrend whereas only a wide variety of sources,and listed 28 (80%) of the 35 nine showedan increase.A further nine speciesshowed an wader speciesin North America as declining.Of these,19 uncleartrend but severalof thesewere alsothought to be in species(54%) showedstatistically significant or persistent decline.More recentdata also suggesta decliningtrend for negativetrends. For somespecies, such as Red Knot, a pre- Curlew Numeniusarquata in Northern Germany (Melter et viously non-significantdeclining trend has sharpenedand al. 1998) andfor RingedPlover Charadriushiaticula around this speciesseems to be in steepdecline in the New World the North Sea (Hfilterlein et al. 2000). as well as the Old World (Baker et al. 2000). Gilissen et al. (2002) reporteda sharpdecrease in the Most American shorebirdsare long-distancemigrants numberof non-breedingRed Knot Calidris canutusin The from Arctic and sub-Arctic breeding grounds,which are Netherlandsbetween 2000 and 2002 (source:T. Piersma in monitoredby a number of schemesduring the breeding, litt.). Similarly, Red Knot in the neighbouringvery impor- migration and non-breedingseasons. The Western Hemi- tant stagingarea of the Schleswig-HolsteinWadden Sea sphereShorebird Reserve Network (WHSRN) is the largestof showed a decline between 1988 and 1999 of about 35% these,and includes54 sites(see: http://www.manomet.org/ (GQnther& R6sner 2000). WHSRN/leam.php).American and Canadian biologists have Of 21 wader species monitored over 12 years in the developeda methodfor monitoringArctic waderpopulations WaddenSea, only five have increasedwhereas nine species in the breeding season,and are trying to establish a har- have shownpersistent declines. GQnther & R6sner (2000) monised monitoring programme for all North American recordeddecreases in five Arctic-breedingspecies of which breedingpopulations (Johnston 2001, Skagen,this volume). four were wadersthat had previouslybeen increasing (Grey Efforts are also being made to establish IWC in North Plover Pluvialis squatarola, Red Knot, Dunlin Calidris America, which remainsthe most sizeablegap in the net- alpina and RedshankTringa totanus). They related these work. IWC is well establishedin partsof SouthAmerica, but trendsto possiblechanges in the climate.Data from Zacken- monitoring in the Caribbean and in Central and South berg in the central high Arctic of Greenlandalso showed America remains small in scale, and the proportion of decreasingnumbers of RedKnot during 1995-2002 but stable waterbird populationsfor which estimatesare available is or increasingnumbers of five othershorebird species breed- lower in the Neotropicalregion than in any of the