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Table I. Annual variation in the biomass of prev species of Knol Calidris canutus ig AFDW m -'i.n sue N in August of 1977 to 1986. Average, lowest and highesi hiomass are given. RSD: relative standard deviation (SD as percentage of the mean i. Spei ies Average, g Range, g RSD.% Macoma 17.22 7.4- 34.5 4(.(. Cera.sioilenna 20.66 0- 62.3 107.2 Mya 13.20 7ii 23.7 38.6 Si nihil ularia 20.2.1 8.1- 46.3 86.S Msiilus 1.45 0- 7.9 186.6 Total 73.26 52.X-111.0 26.6 Table 2. Annual variation in the biomass within the range of size classes harvestable bj Knot Calidris canutus ig AFDW m -: without depth restriction) al she N in August of 1977 to 1986, Range ol hat vestable si/e classes are laken from Zwarts & Blomerl (1992). Ai erage. lowest and highest biomass harvestable by Knot are given. RSD: relative standard deviation (SD as percentage of the mean). Species nge, mm Average, ? Range, % RSD, '. Macoma 6-16 7.81 3.9-14.9 44.0 Cerastoderma 5-12 1.25 (i 6.6 155.7 Mya 7-17 0.33 0- 1.3 153.4 Si nihil ularia 7-14 0.14 0- 1.4 .'00.0 Mytilus 5-20 0.33 0- 2.6 2377) Total 9.86 3.9-17.7 45.9 biomass. The biomass of these species did not deviate much, however, from the values found in other, similarly sheltered areas wilh mixed substrate, situated at or just above mean sea level (Beukema 1976. Zwarts 1988b). Knot do not swallow large prey and they ignore the small si/e classes (Zwarts & Blomert 1992). Table 2 gives the range of size classes harvestable bv Knol and the corresponding biomass for these size classes at site N. A comparison of Tables I & 2 reveals that onlv a small fraction of the total biomass fell within die range of size classes harvestable by Knot. The exception vv as Macoma. for which, on average. 449f of ihe total biomass may be considered as harvestable by Knot. VARIATION IN FOOD SUPPLY OF KNOT 292 Moreover, of all the potential prey species, the annual variation in harvestable biomass is least in Macoma. The large annual variation in total food supply was caused by the erratic occurrence of summer recruitment and winter mortality (Beukema et al. 1978, Beukema 1979. 1982. Beukema & Essink 1986, Desprez «?/ al. 1991, Ducrotoy el al. 1991, Essink et al. 1991. Jones & Park 1991. Obert & Michaelis 1991). There were also large differences among species in annual growth rale and mortality (Fig. 4). Cerastoderma grew rapidly but the majority died within two or three years. There was recruitment in this species during seven of the ten years, but the only substantial cohort originated in 1984. No spatfall of any significance occurred in Scrobicularia during ihe ten years after 1976. when a strong year class was recruited (see also Essink et al. 1991). Many of these animals were still alive in 1983 and 1984. In Mya as well, there was heavy spatfall during only one of the ten years, viz. 1979. Recruitment was variable in Macoma. but the variation was not as large as in the other species: in six of the ten years there was recruitment, with a considerable spatfall occurring in three of them. Food of Knot After the first growing season. Mya reached A si/e of 5 lo 10 mm and grew io about 25 mm by the end of their -econd summer (Figs. 4 & 5). This means that the majority of the first-year animals were ignored by Knot since they were too small and therefore unprofitable, while by the end of the next growing season they had become too large to be sw allowed. For ihe same reason, onlv die largest Cerastoderma and Msiilus in their first year and the most slowly growing individuals in their second year were potential prey for Knot. However. Knot were able to feed on Macoma over a much longer period, as it took a cohort of ibis species four years to pass through the 'window of predation" digs. 4&5). The potential importance of Macoma as prey is also clear from Fig. 6. which shows the annual variation in biomass of the si/e classes harvestable by Knot. The other prey contributed, on average, only 2\ c
20 30 VARIATION IN FOOD SUPPLY OF KNOT 10 20 30 shell size (mm) I in. 4. Densit] i B m i of five bivalve species at site N in August during ten years (1977 to 1986). The si/e classes harvesiable by Knot Calidris canutus (i.e. not too small to be unprofitable or too large to be ingestible or accessible I are indicated b) vertical are) ban i from/warts A: Blomen 1992). Data for 1977 arc not directly comparable with the following years since ihc samples were taken from a target area 293
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WADERS AND THEIR ESTUARINE FOOD SUP
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plia^ohi. WADERS AND THEIR ESTUARI
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Waders and their estuarine food sup
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WADERS AND THEIR ESTUARINE FOOD SUP
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figuren: Dick Visser omslagfoto: Ja
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15 Versatility of male curlews (Num
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That science is making progress, ma
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INTRODUCTION The remnants of brushw
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When hcnlhic bivalves extend llien
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the burrow depths and on the fracti
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INTRODUCTION Ms,i invest 409 of (he
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able lo sw itch 10 oiher prey which
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Long-term, broadly-based research c
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Chapter 1 SEASONAL VARIATION IN BOD
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SEASONAL VARIATION IN BODY WEIGHT O
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Tahle 1 Weight loss ('•- ± SE) m
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i 60 50 40 30 20 10 0 • INFESTED
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240- SEASONAL VARIATION IN BODY WEI
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20 10 0 -10 -20h 2 3 4 5 6 7 8 9 se
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a E 400 - S. plana 35 mm 320 240 16
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Chapter 2 HOW THE FOOD SUPPLY HARVE
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FOOD SUPPLY HARVESTABLE BY WADERS H
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Methods The study sites were situat
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less than that of bivalves, partly
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I Fig. 3). Peak condition was reach
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total biomass since most of those t
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on the basis of the preceding and t
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However, for obvious reasons, we ma
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prey. A decrease in the prey densit
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Tahle 2. The intake rate ol < lyste
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* ' % -. . ; a X - . - * • ^ •
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(Zwarts & Wanink 1989). In quiet we
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general law relating handling time
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nearly twice as much time (0.79 s).
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4 5 6 7 8 9 size class of Corophium
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and annually. Second, the lower siz
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Prey switching Waders feeding on ti
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autumn and spring, and the contrary
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where they switch to surface-living
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Chapter 3 BURYING DEPTH OF THE BENT
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DEPTH AND SIPHON CROPPING IN SCROBI
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I DEPTH AND SIPHON CROPPING IN SCRO
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DEPTH AND SIPHON CROPPING IN SCROBI
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Table 3. Three-Way analysis Of vari
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Chapter 4 SIPHON SIZE AND BURYING D
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15 20 size (mm) Fig. 3. Cerasioderm
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10 size (mm) SIPHON SIZE AND DEPTH
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o, 7 01 5 | * CL 5- SIPHON SIZE AND
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4 Q) Si •a a. 16- 20- A predator:
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prey risk for an animal al a depth
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Table 6. Size al which there is a m
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* ' 1 /-/ "».-^*«C
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face and so expose themselves to a
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surface in die containers was varie
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50 OOF 310.00 I 5.00 ^ 1.00 3=" 0.5
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Tahle 1. Macoma and Scrobicularia.
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siphon would not have to reach the
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known siphon weight and burying dep
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ACCESSIBLE PREY ARE OFTEN IN POOR C
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1 2 3 4 burying depth (cm) Kin. I.
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I—1 • • : : : : ! - ! -|-r 0
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Chapter 7 DOES AN OPTIMALLY FORAGIN
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OPTIMAL FORAGING AND THE FUNCTIONAL
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100 200 300 prey density (n-m-2) Fi
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Table I. Results of five one way an
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Table 2. Results of eight iwo-wav a
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prey density II III Fig. 12. Freque
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PREY SIZE SELECTION AND INTAKE RATE
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Predicted 'passive size selection'
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lig. 2. Larger Mussels are less ava
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Fig. 5. Scrobicularia plana. Size c
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and maiiv are too thick-shelled to
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The measurements of handling time i
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1 2 3 4 5 6 7 probing depth (cm PRE
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valves may vary by a factor of two
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optimal foraging model, the minimum
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their gut is full? Do they reduce t
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PREY PROFITABILITY AND INTAKE RATE
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catchers to take only certain prey
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licult error of estimate arose if p
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Counts of feeding and non-feeding b
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20 30 40 50 shell length (mm) PREY
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Nereis Arenicola tipuia earthwo'm M
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take rate. We might therefore expec
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prey species, using parallel slopes
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5.0 4.0 1-3.0 a & • % * • * •
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time during the feeding period. As
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winter. Similarly, handling time in
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5.0 - f-4.0 S 3.0 in I 20 a 2 a | 1
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situation arrived in the western pa
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• ' • 14 PREY PROFITABILITY AND
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Notes lo appendix: PREY PROFITABILI
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Chapter 10 WHY OYSTERCATCHERS HAEMA
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2 4 6 8 10 time on feeding area (h)
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80- 60- o 80 60- 40- 20- INTAKE RAT
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est of bod\ behind: an estimated 22
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INTAKE RATE AND PROCESSING RATE IN
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Wanink 1993). The energy content of
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(7) Age All studies dealt with adul
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irds over long periods. As an examp
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Discussion There is no difference i
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comparison between the weight of ih
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. 1', L ! •
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Introduction PREDICTING SEASONAL AN
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PREDICTING SEASONAL AND ANNUAL FLUC
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Page 238 and 239: PREDICTING SEASONAL AND ANNUAL FLUC
Page 240 and 241: 1000 r 1 II" 1 - r^Jan'80 PREDICTIN
Page 252 and 253: IOO BO 60 40 20 0 PREDICTING SEASON
Page 265 and 266: WHY KNOT TAKE MEDIUM-SIZED MACOMA W
Page 267 and 268: in Zwarts & Esselink 1989). The len
Page 269 and 270: shell length (mm) FIR. 3. Peringia.
Page 271 and 272: fused, specimens larger than this w
Page 273 and 274: 50 100- s s I — f = S. plana, n=2
Page 275 and 276: area is twice as large as the touch
Page 277 and 278: 10 15 lower size threshold (mm) Fig
Page 279 and 280: lime (Hughes 1979). This would furt
Page 281 and 282: WHY KNOT TAKE MEDIUM-SIZED MACOMA T
Page 283 and 284: Chapter 13 ANNUAL AND SEASONAL VARI
Page 285 and 286: VARIATION IN FOOD SUPPLY OF KNOT AN
Page 287: Two sites (N and M in Fig. 2) were
Page 291 and 292: 20 l i r'l ' i •o j^y^T n ^ ' " ^
Page 293 and 294: July ' Aug ' Sept Fig. 9. Proportio
Page 295 and 296: available. There must, however, be
Page 297 and 298: Chapter 14 SEASONAL TREND IN BURROW
Page 299 and 300: BURROWING AND FEEDING IN NEREIS SEA
Page 301 and 302: Table 2. Results of a 2-way analysi
Page 303 and 304: June 1981 June 1982 is * N.MUD •
Page 305 and 306: 8 10 I 12 JZ 5. -g 1*» •e o i 16
Page 307 and 308: 6 - n=!080 5 • g 4 CP > i 3 CO CD
Page 309 and 310: 1985) and Curlew (/wails ,v, Lsseli
Page 311: Chapter 15 VERSATILITY OF MALE CURL
Page 314 and 315: Smid! 1951. Muus 1967, Wolff 1973,
Page 316 and 317: 0.6 0.8 1.0 1.2 1.4 1.6 jaw lengih
Page 318 and 319: Na oi both Nrieck Fig. 7. Numenius
Page 320 and 321: 6 8 10 12 14 16 18 worm length (cm)
Page 322 and 323: too (Fig. 11 A). Indeed, the averag
Page 324 and 325: VERSATILITY OF CURLEWS FEEDING ON N
Page 326 and 327: total time spent al the surface. Th
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Page 331 and 332: PREY DEPLETION BY OYSTERCATCHER AND
Page 333 and 334: the rule: the observed lower limit
Page 335 and 336: to locate the clams after they had
Page 337 and 338: Curlew, by bury ing some hundreds o
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PREY DEPLETION BY OYSTERCATCHER AND
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SAMENVATTING 345
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Voorgeschiedenis In 1960 verscheen
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maken. Als gebied A een grotere voe
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omdat ze nog vrijwel niets wegen. l
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kunnen opzuigen. of diep leven en z
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van de uitgerekte sifo over het wad
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het toen niet gemakkelijk hebben ge
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doende nonnetjes van 10 tot 15 mm l
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aangevoerde voedsel en de wulp past
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zijn dan twee jaar en wulpen geen s
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was dan ook dank/ij de inzet van al
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REFERENCES 367
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Allen RL. 1983. Feeding behaviour o
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BreyT. 1989. Der Einfluss physikali
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latie tol chironoiiiiilen en de wai
Page 371 and 372:
huch der Vogel Milteleuropas, Band
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llolmann II. & H. Huerschelmann 196
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l-cndrem D.W. 1984. Flocking, feedi
Page 377 and 378:
Pekkarinen M. 1984. Regeneration of
Page 379 and 380:
lion of Mussels Mytilus edulis hy O
Page 381 and 382:
lulal Dal esiuanes: a comparison of
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