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2 3 4 5 6 7 time after emersion (h) Fig. 9. Nereis ili versicolor. Surface activity on a muddy intertidal Hal after emersion on 9 September (•) and 22 September (O). A. Frequency with which worms > .1 cm were observed al the surface (freq. = no. of observations/mean density; it was assumed thai worms < 3 cm were not detected). B. Duration of ihe surface boots i mean ± SB). C Surface activity as percentage of the time budget (fret), h ' x duraUon of surface bout). riod of 6 li is c. 10 times more than that measured by Twisk (1986) in a more natural experimental selling. The surface activity was. as in the field situation, minimal during the first 2 h after exposure, but the burrow activity was then at its maximum (c. 20%). The time spent on burrow activity decreased during the low BURROWING AND FEEDING IN NEREIS 310 40 - SURFACE 2 3 4 5 time after emersion (h) ® Fig. III. Nereis diversu olor. Time-budgei in an aquarium after cxposure: active ai surface ilighi areal and in burrow (dark). A. COO irol; B. Feeding experiment when a slurry of minced Scrobicularia planavnss poured over the substrate just alter emersion. Standard er- IOIS computed per hall hour periods tn =12). water period, whereas surface activity increased, resulting in an almost constant level of observed activity during the entire exposure time. This pattern of activity changed completely after a slurp, of shelled and minced Scrobicularia plana was poured over ihe mud shortly after emersion (Fig. I OB). Nereis came to the surface immediately to scavenge on the pieces of meat, which they took down into their burrows. The worms spent most ol" their time at the surface during the first 3 h of this experiment. It is unlikely that the decrease in activity after 3 h was caused by a depiction of ihe food supply because of (he large quantity of slurry used in the experiment. Possibly the worms became satiated. There was no burrow activity when there was no water left at the surface (Fig. 11), as also found by Twisk (1986). The observation that burrow activity was maximal if the overlying water layer was thin, might be explained by the increasing food concentra-
6 - n=!080 5 • g 4 CP > i 3 CO CD f 2 L i 0 n=i6M water above thin moist surlace water lilm surface BURROWING AND FEEDING IN NEREIS ^ burrow ^ H surface Fijj. 11, \ereis diveiMiolnr. Activity in an aquarium in relation to water level after exposure, based on acliviiv Counts every 1(1 min In = counts X worms in aquarium I. tion when the depth of the water column decreased, but we cannot exclude the possibility that the burrow activity became more visible. The method used to quantify the activity data in Fig. 11 apparently led to an underestimation compared with the time-budget study (Fig. I0A). This does not. however, change the relath e differences in activity as caused by water level. Discussion Burrow depth and size Burrow depth of Nereis increased with size (Figs. 2 and 3). However, within each size class there was a large variation in burrow depth. A part of this variation can be attributed to body condition: worms with a relatively heavy body weight have deeper burrows than worms in poor condition (Figs. 5 and 6). The difference in burrow depths of worms living in sand and mud (Figs. 2 to 4) might also be explained by systematic differences in body condition for worms living in sand and mud (Fig. 5). There is no reason to assume that deep burrows cause enhanced body condition, so the reverse seems more likely: worms with a poor condilion are apparently not able to dig and/or maintain a deep burrow. In bivalves it was also found that individ 311 uals with a better body condition increase their burying depth, achieving a decrease in their predation risk (Zwarts 1986. Zwarts & Wanink 1989). Burrow depth and predation risk When ihe tidal cycle is simulated in a laboratory, worms remain deep in their burrows and perform no surface activity during immersion (Vader 1964. this paper). If ihis is also the case in the field, depth would determine accessibility to shrimp and fish feeding when the tidal Bats are flooded. Shrimp Crangon cran- It is necessary ID sil quietly lor many hours lo know how often Rag worms come to the surface to feed during the low waler period.
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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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1000 r 1 II" 1 - r^Jan'80 PREDICTIN
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IOO BO 60 40 20 0 PREDICTING SEASON
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Page 256 and 257: PREDICTING SEASONAL AND ANNUAL FLUC
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
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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
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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: 8 10 I 12 JZ 5. -g 1*» •e o i 16
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
Page 328 and 329: 2 4 . • 2.2 • 30 .-.2.0 to Q. 1
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
Page 339 and 340: PREY DEPLETION BY OYSTERCATCHER AND
Page 341 and 342: SAMENVATTING 345
Page 343 and 344: Voorgeschiedenis In 1960 verscheen
Page 345 and 346: maken. Als gebied A een grotere voe
Page 347 and 348: omdat ze nog vrijwel niets wegen. l
Page 349 and 350: kunnen opzuigen. of diep leven en z
Page 351 and 352: van de uitgerekte sifo over het wad
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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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