waders and their estuarine food supplies - Vlaams Instituut voor de ...

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$Wetenschap - \Nijverheid- Handel$

1 2a 2b 2c- 3a 3b 3c 4a 4c 5a 5b 5c Fig. III. Adaptation ol the Oystcicakhci's probing deplh to pay density. Mean probing deplh lOiand lrei|iiency distribution .. h and F. F has OPTIMAL FORAGING AND THE FUNCTIONAL RESPONSE 148 been set to I. for all prey have the same energy value. The value of A. can only be estimated if it is known that the Oystercatcher took all prey encountered. This was definitely the case for the lowest prey densities (Fig. 9). That is why we selected the observations on handling time for the three lowest densities to measure the effect of depth on handling time: h (s) = 3.7 (depth, cm)+ 24.9 (n = 72, r = 0.37. p< 0.005). We are now able to predict the hypoiheiical intake rale. assuming an optimal selection of ihe depth classes by the Oystercatcher. The predicted intake rale for every possible selection level is presented in Fig. II. The margin of the grey field in litis figure connects the predicted maximal intake rales, and thus predicted depth selection for the different prey densities. According to these predictions the Oystercatcher should lake all attainable prey for densities 6 m to 24 in • but ii should successively drop the deep-lying prey from iis diet al higher prey densities. Only deplh class 0 cm should be laken from density 350 cm : onwards. 0 1 2 3 4 5 6 7 maximum prey depth accepted (cm) lig. 11. The opmn ii set of depth classes predicted for al lilies offered. The dots arc solutions ol Eq (3i. The margin of the Held connects values of maximal intake rale for the dillerenl . 10 maximize iis intake rale, the Oysieicalchei should take all the depth classes within the grey field and reject deeper lying prey.
prey density II III Fig. 12. Frequency distribution (% I of depth classes in the Oyster- catcher's diet al font deusiiy classes. 6+ 12 + 24 cm ' (ll. 44 + 88 m : 1111: 175 + 262 in • I III I and 350 * 437 m ; 11V i. Irom Fig. 11 we have calculated which depth classes ihe bird should lake lo ob tain Ihe maximal intake rate (dark grey I and which classes ji might add io the diei i grey i before reducing lis intake rale by more than 5% (white). Observed depth selection and intake rate Figure 12 shows the observed depth selection for four prey density classes. As predicted, the bird look all depth classes at the low prey densities and ignored the deep-lying prey when the density was high. The bud did not show exactly the predicted change in rejection threshold. However, the deviation is small and. as shown in Fig. 11 A. deviation of 2-3 cm from the predicted depth selection limit hardly reduces the iniake rate. The bird added in fact only those depth classes to ihe optimal set by which ihe intake tale was reduced not more than 5' I. The predicted intake tale lot the bird selecting exaclly ihe optimal set of deplh classes Ills quite well wilh the obsened values for the five lower prey densities (Fig. 13). However, from density 175 m : onwards. the number of prey taken by the Oystercatcher rises above the predicted intake rate. The predicted iniake rale was based on ihe assumption that all prey must be laken from the optimal set of depth classes. However, by using as second selection criterion -ignore prey which are closed or noi gaping enough, and so shorten the cutting time- the Oyster OPTIMAL FORAGING AND THE FUNCTIONAL RESPONSE 149 catcher vv as able to reduce the handling time and so increase its intake rate at higher prey densities by as much as 5i)'. of the expected value. A density-related selection of shells which could not be Stabbed immediately has already been suggested by Hulscher (197(1) foi an Oysieicalchei feeding on Cockles all luiiicd al the same deplh. We suggest that al prey densities below 175 in ; optimal depth selection is the only decision rule, but above that density selection on depth as well as on easy' bivalves is optimized. Discussion Rate of discovery a The disc equation of Holling (1959) is attractive because of its simplicity. The intake rate depends on two factors only, which should both be constant for all prey densities: the handling lime and ihe rale of discovery a. Since a equals XI) ' (cf. Fq 2). a will be density-independent only if the search time increases n' limes when prey density increases n limes. This was the casein the "touch experiment' of I lolling (1959) but in the 'sound experiment' described in the same paper, a decreased when density wenl up. Holling solved this problem by dividing ihe search lime into two compo- prey density (n-m-2) Fin- 13. Relationship between intake rale and prey density. Pre dicted values i • rare compared lo ihe mean values, taerved CL. (O).
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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
Page 93 and 94: DEPTH AND SIPHON CROPPING IN SCROBI
Page 95 and 96: Table 3. Three-Way analysis Of vari
Page 97: Chapter 4 SIPHON SIZE AND BURYING D
Page 100 and 101: 15 20 size (mm) Fig. 3. Cerasioderm
Page 102 and 103: 10 size (mm) SIPHON SIZE AND DEPTH
Page 104 and 105: o, 7 01 5 | * CL 5- SIPHON SIZE AND
Page 106 and 107: 4 Q) Si •a a. 16- 20- A predator:
Page 108 and 109: prey risk for an animal al a depth
Page 110 and 111: Table 6. Size al which there is a m
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Page 114 and 115: face and so expose themselves to a
Page 116 and 117: surface in die containers was varie
Page 118 and 119: 50 OOF 310.00 I 5.00 ^ 1.00 3=" 0.5
Page 120 and 121: Tahle 1. Macoma and Scrobicularia.
Page 122 and 123: siphon would not have to reach the
Page 124 and 125: known siphon weight and burying dep
Page 127 and 128: ACCESSIBLE PREY ARE OFTEN IN POOR C
Page 129 and 130: 1 2 3 4 burying depth (cm) Kin. I.
Page 131 and 132: I—1 • • : : : : ! - ! -|-r 0
Page 133 and 134: Chapter 7 DOES AN OPTIMALLY FORAGIN
Page 135 and 136: OPTIMAL FORAGING AND THE FUNCTIONAL
Page 137 and 138: 100 200 300 prey density (n-m-2) Fi
Page 139 and 140: Table I. Results of five one way an
Page 141 and 142: Table 2. Results of eight iwo-wav a
Page 143: OPTIMAL FORAGING AND THE FUNCTIONAL
Page 147 and 148: OPTIMAL FORAGING AND THE FUNCTIONAL
Page 149: PREY SIZE SELECTION AND INTAKE RATE
Page 152 and 153: Predicted 'passive size selection'
Page 154 and 155: lig. 2. Larger Mussels are less ava
Page 156 and 157: Fig. 5. Scrobicularia plana. Size c
Page 158 and 159: and maiiv are too thick-shelled to
Page 160 and 161: The measurements of handling time i
Page 162 and 163: 1 2 3 4 5 6 7 probing depth (cm PRE
Page 164 and 165: valves may vary by a factor of two
Page 166 and 167: optimal foraging model, the minimum
Page 168 and 169: their gut is full? Do they reduce t
Page 171 and 172: PREY PROFITABILITY AND INTAKE RATE
Page 173 and 174: catchers to take only certain prey
Page 175 and 176: licult error of estimate arose if p
Page 177 and 178: Counts of feeding and non-feeding b
Page 181 and 182: 20 30 40 50 shell length (mm) PREY
Page 185 and 186: Nereis Arenicola tipuia earthwo'm M
Page 187 and 188: take rate. We might therefore expec
Page 189 and 190: prey species, using parallel slopes
Page 191 and 192: 5.0 4.0 1-3.0 a & • % * • * •
Page 193 and 194: 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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PREY PROFITABILITY AND INTAKE RATE
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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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WHY KNOT TAKE MEDIUM-SIZED MACOMA W
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in Zwarts & Esselink 1989). The len
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shell length (mm) FIR. 3. Peringia.
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fused, specimens larger than this w
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50 100- s s I — f = S. plana, n=2
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area is twice as large as the touch
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10 15 lower size threshold (mm) Fig
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lime (Hughes 1979). This would furt
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WHY KNOT TAKE MEDIUM-SIZED MACOMA T
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Chapter 13 ANNUAL AND SEASONAL VARI
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VARIATION IN FOOD SUPPLY OF KNOT AN
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Two sites (N and M in Fig. 2) were
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20 30 VARIATION IN FOOD SUPPLY OF K
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20 l i r'l ' i •o j^y^T n ^ ' " ^
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July ' Aug ' Sept Fig. 9. Proportio
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available. There must, however, be
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Chapter 14 SEASONAL TREND IN BURROW
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BURROWING AND FEEDING IN NEREIS SEA
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Table 2. Results of a 2-way analysi
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June 1981 June 1982 is * N.MUD •
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8 10 I 12 JZ 5. -g 1*» •e o i 16
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6 - n=!080 5 • g 4 CP > i 3 CO CD
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1985) and Curlew (/wails ,v, Lsseli
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Chapter 15 VERSATILITY OF MALE CURL
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Smid! 1951. Muus 1967, Wolff 1973,
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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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