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8 10 15 20 shell length (mm) WHY KNOT TAKE MEDIUM-SIZED MACOMA 4 6 8 10 15 20 shell length (mm) 4 6 8 10 15 20 shell length (mm) tiii. 2. Relations between dry weight of the cleaned shell (mg dr) weighl I and shell lengih I upper line), and between flesh weight (mg ash-fiee dry weight) and shell length (lower linei in six hard-shelled species. All dala. except lor Peringia, were collected in the study area in August: data were pooled for 11 years of sampling I Irom /wans I'M I and unpubl.). Data tat Peringia Were taken from Chambers & Milne (1979) and combined lor May and November: a correction is made lor the "' • organic mailer found in ihe shell iDckker 1969). representing 10 lo 15% of Ihe total organic mass. Since the relation between Im shell weighl) and Int lengih) appeared to be concave in Ihe bivalves, I polynomial line was filled. The lunctions were calculated for the means per each mm si/e class, weighted for the number of observations. All correlations were larger than 0.995. The functions are indicated in the panels (y = ln(mg) and x = ln( mini), as well as the number of measurements and the range over which the regressions were calculated. 272
shell length (mm) FIR. 3. Peringia. Size frequency distribution of 450 individuals found in nine gizzards of Knot collected on Vlieland, Dutch Wadden Sea. during the period 15 August to 24 October 1982. Dark shading: snails for which ihe lengih could be determined. Light shading: crushed snails for which width at the base, but not lengih. could be measured and for which length was derived from ihe relationship between width and length in undamaged snails isee righl inset), l-eli inset ShOWl thai in more than half of the snails width nor length could be measured (IIKK^ = 10221. esiimates of shell length give values of average flesh w eight of prey taken by Knot which differ by 50%, due io the fact that llesh weight aUometrically relates to shell length with a power of 2.14 (Fig. 21. Prey selection According to our observations, not all prey taken from the mud were actuallv swallowed: 63 of the 84 Macoma brought to the surface, were ingested, and only one in four of the Cerastoderma. Two shrimps Crangon crangon 5 cm long were handled for several seconds but finally not eaten. Rejection of the latter two WHY KNOT TAKE MEDIUM-SIZED MACOMA 273 prey species was unexpected as Cerastoderma is a major prey elsewhere (Goss-Custard el al. 1977b. Boere & Smit 1980. Nehls 1992) and faecal analysis showed that Knot can \'ccs\ on shrimps 43 to 63 mm long (own unpubl. data). Both the Held obsct vations and faecal analysis indicate that Macoma was the main prey and that Cerasioderma. Nereis and Comphium were rarely taken (Table 2). Even though very few of the prey seen eaten were too small to identify. 360 Mud Snails Peringia 11 to 3 mm) and six very small bivalves 11 to 2 mm) were found in the faeces. However, all were intact and contained flesh, so they must have been accidentally scraped from the surface while the faeces were being collected. One of the Knot observed produced 15 faeces during 21 min of continuous observation. All but one of the intervals between faeces depositions varied between 58 and 88 s. The exception was 174 s long, suggesting that we missed one faecal packet during one interval. If so. Knot produced one faecal packet per 80s. Therefore the faeces that were collected reflected a period of 20 x 80 s. or 26 min, feeding. Since the lotal time spent watching the birds was 83 min. the number of prey seen taken should have been 83/26 or 3.2 times as large as the number found in the faeces, and Table 2. Prey taken by Knot during 82 min (left column i and prev found in 20 faeces from the same individuals t right column I. W'leuuiier Hats. Dutch Wadden Sea. 4 August 1983. Among the prey taken, three were so small that the species could not be identified, The number ol prev in the faeces was determined by counting unique fragments (jaw S ol the Ragworm Nereis, second antennae of •niiirn. umbos of Macoma and Cerastoderma); since each animal has two such fragments, the numbers found were divided by two. Animals accidentally scraped from the surface arc indicated in parentheses v.. prey Ho pies in faeces Macoma >9 mm 63 19 Cerastoderma 12 mm 1 0.5 Nereis I 0J Corophium 3 05 Macoma spat 1 I2i • derma spa! » ,4, Peringia J (360)
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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
Page 218 and 219: Wanink 1993). The energy content of
Page 220 and 221: (7) Age All studies dealt with adul
Page 222 and 223: irds over long periods. As an examp
Page 224 and 225: Discussion There is no difference i
Page 226 and 227: comparison between the weight of ih
Page 228 and 229: . 1', L ! •
Page 230 and 231: Introduction PREDICTING SEASONAL AN
Page 232 and 233: 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: in Zwarts & Esselink 1989). The len
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 and 288: Two sites (N and M in Fig. 2) were
Page 289 and 290: 20 30 VARIATION IN FOOD SUPPLY OF K
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
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Na oi both Nrieck Fig. 7. Numenius
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6 8 10 12 14 16 18 worm length (cm)
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too (Fig. 11 A). Indeed, the averag
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VERSATILITY OF CURLEWS FEEDING ON N
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total time spent al the surface. Th
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2 4 . • 2.2 • 30 .-.2.0 to Q. 1
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PREY DEPLETION BY OYSTERCATCHER AND
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the rule: the observed lower limit
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to locate the clams after they had
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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
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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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