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•(C) 0) a E C 0 2 4 6 B 10 12 biomass (g M. balthica-m 2 ) harvestable for knol VARIATION IN FOOD SUPPLY OF KNOT l in. 7. Calidris canutus. Aggregative response of Knot in relation lo spatial variations in the harvestable lood supply ig AFDW m ' of Macoma 6 to !'• mm long living in the upper 2 cm of ihe substrate; oil', ofihc prev were found in Ihe upper 2 cm I. The data reter to 146 plots Of 0.1 ha at sites N and M Irom July to September 1981: I09.S samples of 1/56 nr' were laken. A. Average feeding density, calcu lated over 67 counts made during seven lov- water periods. B. Fre quency Of occurrence (percent of low-water periods during which one or more Knol were counted). (.". Avenge number tnumber of Knol seen in a ploi when the number of Knot was > I). Knot return to sites with a high food supply The distribution of Knot over the feeding area in relation to the density of their harvestable prey was investigated in late summer 1981. The biomass harvestable by Knol varied between 2 and 12 g AFDW m -. and the density of Knot increased with food supply over this range (Fig. 7A). Such an aggregative response of predators to spatial variations in prey density can be div ided into two components: the frequency with which the predators occur and the numbers present on any 296 one occasion. In the case of Knot (Fig. 7A). the response was not determined by the numbers of birds present at any one time (Fig. 7C). but by the frequency with which they occurred in a plot (Fig. 7B). This was perhaps to be expected, in view of the observation that Knot almost always fed in Hocks which were alw aj s on the move, even on a scale of less than an hour. They moved readily from one locality to another, probably continuously seeking the most rewarding place (Goss-Custard 1970b. Gerritsen etal. 1983). Knol found the best parts of the feeding area by ignoring, or rapidl) traversing, marginal areas tFig. 7B). Annual food supply and number of Knot Macoma did not grow between July and November (Fig. 5) and there was no decrease in densities during these months (Zwarts et at. I996h). Nonetheless, the food supply harvestable by Knol decreased over the period, for two reasons. Firstly, the biomass of individual prey, or their condition, decreased by 20 to 30%. although this seasonal trend was small in comparison wilh annual differences (Fig. 8). Secondly, the proportion of Macoma living in the upper two cm of die substrate, and thus within reach of the bill of Knol, de- •18 a •;•: _ e ? S3 o 40 " M F Mi r 81 Kl 36 . K • u ith p. £ ~o 20 U Ul 0) 24 1? I BU 20 July Aug Sep Oct Nov Fig. 8. Macoma. Body weighl (mg AFDW) of individuals 15 mm long in Ihe study area during late summer and autumn between 1976 and 19X6 (based on/wans 19911.
July ' Aug ' Sept Fig. 9. Proportion of Macoma accessible to Knot Calidris caniiius. i.e. prev living in the upper 2 cm (dark shadingi and upper .1 cm (dark + light shading i ol ihe substrate: measurements laken in the study area Irom 1980 lo I9S6 ibased on ZwartS & Wamnk 1989), creased during the season (Fig. 9). However, there were also considerable differences among years in depth distribution. In 1984, the majority of prey remained within reach of the bill until October, whereas in 1980 and 1986. Macoma were beyond reach of the bill from August onwards. The accessible fraction therefore decreased gradually over the course of the season, but 1985 was an exception since Macoma lived at a greater depth in August than in September. Figure 10 shows the decrease in biomass of Macoma harvestable by Knot. This figure combines the measurements of prey density (Fig. 4). prev weight (Fig. 8) and the proportion of prey actually within VARIATION IN FOOD SUPPLY OF KNOT 297 reach of Knot (Fig. 9). Figure 10 also shows when Knot occurred in the study sue in the different years. It is evident that the numbers of Knot feeding were closely related to the annual variation in biomass of Macoma harvestable by Knot. 10 COUNTS '985 July ' Aug ' Sept ' Oct ' Nov Fig. 10. Biomass ,,| 1/,/. ,mui (g AFDW m 2 of individuals 6 lo 16 mm long living in the upper 2 tan) harvestable by Knol Calidris animus al site N. and occurrence of Knot in Ihe study area during late summer and autumn of 1980 to I9H6.
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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
Page 242 and 243: PREDICTING SEASONAL AND ANNUAL FLUC
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 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: 20 l i r'l ' i •o j^y^T n ^ ' " ^
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
Page 339 and 340: PREY DEPLETION BY OYSTERCATCHER AND
Page 341 and 342: 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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