Information About the Habitat Use of Salines and Fish Ponds by Wintering
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Informationabout the habitatuse of salinesand fish pondsby winteringwaders in CadizBay, southwest Spain A. Perez-Hurtado & F. Hortas Perez-Hurtado,A. & Hortas,F. 1991. Informationabout the habitat use of salinesand fish ponds bywintering waders in CadizBay, southwest Spain. WaderStudy Group Bull. 66: 48-53. CadizBay, recently declared as a NaturalPark, is an importantarea for wintering waders in Spain. In the lastfew years mudflats and salines in Cadiz Bay have been claimed for human activities with adverseimpacts on their shorebird populations. Thus, the importance to shorebirdsof thesalines andfish ponds adjacent to theBay could be increasingif they are usedas alternativefeeding areas. In generalthe birds used the salines and fish ponds both for feeding and roosting: some 66% of wadersin salinesat lowtide were feeding. However,not all the birdsused the differenthabitats in thesame way or at thesame state of tide. Someimplications of the usemade by waders of these areasto theirenergetic requirements, morphological adaptations and prey availability are discussed. A. Perez-Hurtado& F. Hodas,Laboratorio de BiologiaMarina, Apto. de Fisiologiay Biologia Animal,Facultad de Biologia,Universidad de Sevilla,Aptdo 1095, E-41080, Spain. INTRODUCTION Thewetlands of CadizBay (between 36ø23'N, 6ø08'W and 36ø37'N,6ø15'W, southwest Spain) extend over 18,000 ha, sall•es la tapa andinclude many different and productivehabitats; intertidal mudflats,salines, fish ponds, lagoons and semi-natural salt marshes(Figure 1). Thesesupport a largenumber of winter- ingwaders (30,000 birds approximately, Alberto et al. 1987). Dueto the strategicgeographic position of the Bayon the fishpond EastAtlantic Flyway it is possiblyan importantstaging area for Study area migratingwaders. Nonetheless,only a fewgeneral studies have been under- takenin relationto thewader populations of CadizBay and theirlinks with other Iberian wetlands (Alberto & Velasco 1988;Dugan 1980; Hortas 1990; Smit in press).There has also been little work on the use that some waders make of the feedinghabitats here (Perez-Hurtado & Garcia1990; Perez -Hurtado& Hortas1990). Although10,000 ha of CadizBay have recently been declared a NaturalPark, a greatnumber of changeshave taken place overthe last20 yearsof humanactivity in thesalines and mudflats.A highproportion of salines(62% of theoriginal area) havebeen deserted or drainedand, in somecases, the pondshave been filled to allowhouse building. Other ponds Figure1. Locationof CadizBay in the EastAtlantic Flyway (inset) and the havebeen deepened and transformed into fish ponds (25% of distributionof differenthabitats in the Bay. The mapalso shows the study thearea). Thesechanges clearly affect the waders using areasselected: 'Salinas la Tapa'and the fishpond study area. these areas. Keyto habitattypes The humanmanagement regime in the remaining fish ponds Salinas alsostrongly affects birds. In general,ponds are emptied in • •lsnponds ":• lost salinas ,Cities 48 tonnes and holds about 10% of the total number of waders in I•IONTH•POND-qTATU9 LOWTIDE I IllOHTIDE the Bay. Forcensusing and studying bird distribution, we also made observations on the mud beside Guadalete River close to thesesalines. Finally, we selecteda representativefish pondand mudflat area close to PuertoReal village (Figure 1 ). - •R• WA•• • ..... ;. •:-,,..[ ,............... " ..... * ...... 1 • T• i FE•U•Y I In thesehabitats, data were collected in goodweather conditionsat lowtide, in Decemberor earlyJanuary, when winteringnumbers are morestable in CadizBay. We also collectedqualitative information about habitat use, at hightide, •TI• inthe fishpond area selected. To understandthe habitatsused by differentwaders, we recordedthe locationsof thoseobserved on habitatmaps. We identifiedfour habitat categories: mudflats, walls (with and Figure2. Annualmanagement regime of the fishponds in termsof water withoutvegetation) and five sub-categories of ponds: level,season and tidal cycle. Type0 = Wet groundbut no water Type1 = Shallowwater < 3 cm Octoberor Novemberto collectfish; after, this, pond sluices Type2 = Waterlevel 3-11 cm areopened and sea-water can move in and out with the tide. Type3 = Waterlevel 11-20 cm Duringthis period, from November to February,a large Type4 = Waterlevel > 20 cm amountof marinenutrients enter the pondswith the tide, perhapsaugmenting the production of preybiomass. From Februaryto thefollowing October, the sluices of the pondare LEVEL 0 LEVEL 1 closedto allowfish cultivation (Figure 2). The mudflatshave been adapted for the culture of thebivalve molluscVenerupis semidecussata in twoways that reduce preyavailability to wadersconsiderably. The mud is removed andmixed with gravel, creating a newsurface layer to a depth of approximately12 cm. In somecases, nets are alsoplaced on the surface. We thinkthat the importanceto shorebirdsof the salinesand LEVEL 2 LEVEL fishpond habitats comes from their use as alternativefeeding groundswhich may help waders to obtaintheir daily energy requirementswhen feeding opportunities are limitedon the mudflats.Given the changesin the habitatsthat have taken place,it isvery important to knowhow bird numbers and distributionhave changed in thearea over recent years and how waders use these habitats. The aim of this work was thusto investigatethe useby birds of twocontrasting habitats in CadizBay: a modernsalina and a representativefish pond (Figure1). Someimplications related to tidalcycle, morpho- logicaladaptations and energetic requirements are also Figure3. Fourcategories for estimationof waterlevel in pondsin relationto discussed. the Black-wingedStilt leg. Type0 = Wet groundbut no water Type1 = Shallowwater < 3 cm METHODS Type2 = Waterlevel 3-11 cm Type3 = Waterlevel 11-20 cm The data were collected each winter in a modern salina from 1987,and ina representativemarine culture (fish pond) area from 1988. To make the observations we used two 15 x 60 The habitat and water level were recorded for each bird telescopesand a carto movethrough the area. observed.To estimatewater level we useda scoringsystem basedon the mean'leg level' of birdsfeeding in the pond, We selectedone of thetypical modern salines in the Bay. The dividedinto four categories (Figure 2). Birdactivity was 'Salinasla Tapa'has a highsalt production, of about40,000 scoredas feedingor notfeeding. 49 Table1. Habitatpreferences offeeding wading birds at lowtide in 'Salinas la Tapa' (S) and the mudflats of theGuadalete River (M) in Cadiz Bay. The estimated numbersare basedon peakcounts from the Decemberor Januarycensus. Winter 1987/88 Winter 1988/89 Winter 1989/90 Winter 1990/91 M S %(M) %(S) M S %(M) %(S) M S %(M)%(S) M S%(M) %(S) Haernatopusostralegus 4 100 5 1O0 Himantopushirnantopus 6 1O0 31 1O0 42 100 20 100 Recurvirostra avosetta 197 100 1 285 3 99 69 160 30 70 1 300 3 996 Charadrius hiaticula 67 57 54 46 82 65 56 44 16 113 12 82 223 100 Charadrius alexandrinus 151 172 47 53 140 134 52 48 103 289 26 74 434 58 88 12 Pluvialissquatarola 16 29 36 64 64 67 49 51 36 91 28 72 50 89 36 64 Calidris alba 6 4 60 40 19 100 5 10 33 67 55 30 65 35 Calidris minuta 2 35 5 95 21 100 15 100 8 21 28 72 Calidds ferruginea 1 28 3 97 15 10 60 40 4 4 50 50 3 1O0 Calidrisalpina 40 505 7 93 399 411 49 51 247 661 27 73 1287 98 93 7 L/rnosa lirnosa 395 1O0 1 146 7 99 120 100 146 1O0 Lirnosalapponica 1 1O0 21 1 96 4 2 1O0 Tringa totanus 65 150 31 68 175 54 76 24 52 106 33 67 230 99 70 30 Arenaria interpres 1 1O0 6 3 67 33 2 1 67 33 6 100 TOTAL WADERS 348 1580 927 1228 541 1614 2299 861 HABITAT USE (%) 18 82 43 57 25 75 73 27 RESULTS AND DISCUSSION KentishPlover Charadrius alexandrinus, Dunlin Calidris alpina,and Sanderling Calidris alba) fed on mudflatsat low The importanceof thesalines and fish ponds for feeding tide(Table 1) butin the salinesand fish ponds for the restof variesgreatly between species. In 'Salinasla Tapa',Oyster- theday. Rufino(1984) showed similar patterns to thosefound catcherHaematopus ostralegus, Bar-tailed Godwit Lirnosa here for KentishPlover, Bar-tailed Godwitand Black-tailed lapponica,Grey Plover Pluvialis squatarola and Turnstone Godwitin the Algarye of SouthPortugal. In generalthe Arenariainterpres, mainly concentrated their feeding on the salinesare used at alltimes of dayby waders for feeding and mudflatsat lowtide. Otherssuch as Black-wingedStilt forroosting. They are alsoused at night(Rufino et al. 1984; Hirnantopushirnantopus, Black-tailed Godwit Lirnosa limosa, Batty1988). LittleStint Calidrisminuta and AvocetRecurvirostra avosetta, fednearly exclusively inthe salines and fish ponds (Table 1) Theproportion of birdsin 'Salinas la Tapa'which were feeding wasabout 66% at lowwater (Table 2 & 4). The habitats Severalsmall species (Ringed Plover Charadrius hiaticula, selectedmost frequently were ponds with a wetsubstrate, but Table2. Numbersof birdsfeeding and not feeding at lowtide in 'Salinasla Tapa'. January1989 January1990 January1991 Feeding Not Feeding Not Feeding Not feeding feeding feeding Haernatopusostralegus H/mantopushimantopus 66 2 10 6 3 17 Recurviros tra a vos etta 65 125 4 125 1 275 Charadrius hiaticula , 43 61 95 26 Charadrius alexandrinus 1O0 269 153 56 58 Pluvialissquatarola 98 8 76 2 87 Calidris alba 6 3 10 30 Calidris rninuta 17 13 21 Calidrisferruginea 5 2 Calidrisalpina 527 795 76 22 L/mosa limosa 159 81 27 119 L/mosa lapponica Tringa totanus 125 4 70 4 89 4 Arenaria interpres 2 TOTAL WADERS 1115 562 1241 293 307 524 ACTIVITY PERCENTAGES 66.5 33.5 80.9 19.1 37.0 63.0 50 Table3. Habitattypes selected bywaders atlow tide in 'Salinas