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Tabic 3. Average intake rale Img s ' ± SD) and prey weight per prev Species; n is the number of studies i given in appendix). Eleven stud ies « uh a feeding period < 1 h and two studies with extremely low intake rates inrs. 190 & 197 in appendix) have been excluded. S/.i cii v mgr> SD mg PI Anadara 1.85 1637 1 Arenicola 2.96 1.64 216 j Cerastoderma 2.17 0.93 230 4S Eanhworms 1.18 0.5.' 71 5 Littorina IM 0.27 138 8 Macoma 2.34 0.59 67 12 Mya 3.14 0.64 172 3 Mytilus ventral 2.04 0.92 418 26 Mytilus dorsal 2.10 0.93 513 27 Mytilus si,,h 2.05 0.69 409 4S :.mi 0.95 61 23 Patella 2.35 120 1 Scrobicularia 1.74 (1.75 178 11 Tipula 1.34 11.48 53 IS Uca 1.78 78 dl all species 2.00 0.85 24(1 12 armoured prey species, and (4) intake rate differed between the species when prey of similar weight were taken. Table 3 gives the average intake rate per prey species. According to a one-way analysis of variance, the differences were significant (R 2 = 0.185, p < 0.0()I. n = 240). The highest intake rate was found in birds feeding on Mya or Arenicola and the lowest in birds eating earthworms. Tipula or Littorina. Since intake rate increased with prey weight in each prey species, a similar relationship might be expected between average intake rate and average weight across prey species. There was. however, no such relationship (r • 0.00). But in order to rule out any possible effect of prey si/e on intake rate, the intake rate was standardized to a prey weight of 200 mg. using the predicted values from the multiple regressions with a common slope but different intercepts for the different soft-bodied and armoured prey species. Intake rate averaged for each species now differed more from each other. In conclusion, prey weighl determines to a large degree the intake rate, but differences between the prey species are even larger. PREY PROFITABILITY AND INTAKE RATE 194 Intake rate and prey density A review of the effect of prey density on intake rate was only attempted for Oystercatchers feeding Cockles. We selected len cockle studies, from the 12 available. As discussed b\ Zwarts et al. (1996b) intake ratewas presumably overestimated by Goss-Custard (1977). while Triplet (1994a) does not present sufficient details to be included in the analysis. If birds do not vary their search rate and prey selection with prey density, a type 2 functional response would be expected (Holling 1959). Although the levelling off in the intake rate al high prey density in the experiments of Hulscher (1976) resembled this type of response (redrawn in Fig. 16). the assumptions underlying the model were not met (Wanink & Zwarts 1985). As had already been suggested by Hulscher (1976). the birds increasingly specialized on easy prey with short handling times when prey density increased. Thus, even in a controlled experiment. Holling"s functional response equation was too simple to describe the reeding behav iour of Oystercatchers. The situation in the wild is still more complicated, because changes in prey density are usually accompanied by variation in prev condition and prey size (e.g. Goss-Custard 1977, Sutherland 1982a). Sutherland (1982a. b) compared the feeding behaviour of Oystercatchers visiting 12 plots where the cockle density varied between 10 and 600 prey m " 2 . He found a levelling off in the feeding rate at about 9 Cockles min" 1 . However, the highest intake rate was achieved at low prey densities because prey were large where their density was low: r = -0.90 for ln(density) against prey weight. A multiple regression analysis revealed that the intake rate was highly dependent on prey weight (R 2 = 0.417, p = 0.0(X)2) as well as on prey density (R 2 = 0.407, p = 0.001). With the exception of the plot with the lowest prey density of 10 Cockles nr 2 , all these values of intake rate fitted rather well with the general relationship between intake rate and prey weight (Fig. 13). Intake rate as a function of prey weight and density has also been calculated in a multiple regression of the combined data set for the 38 measurements taken from the ten studies on cockle-feeding birds depicted in Fig. 16. Again, the effect of prey weight was highly significant (R 2 = 0.577, p < 0.001) as well as prey density (R 2 = 0.093. p = 0.004), with a highly negative correlation between ln(density) and In(prey weight) (r =
5.0 4.0 1-3.0 a & • % * • * • • 'in 20 "*. CD 2 £ 1 0 ct> 1 0.8 • PREY PROFITABILITY AND INTAKE RATE • * * prey weight (mg) • •
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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
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 and 144: OPTIMAL FORAGING AND THE FUNCTIONAL
Page 145 and 146: prey density II III Fig. 12. Freque
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: prey species, using parallel slopes
Page 193 and 194: time during the feeding period. As
Page 195 and 196: winter. Similarly, handling time in
Page 197 and 198: 5.0 - f-4.0 S 3.0 in I 20 a 2 a | 1
Page 199 and 200: situation arrived in the western pa
Page 203 and 204: • ' • 14 PREY PROFITABILITY AND
Page 205 and 206: Notes lo appendix: PREY PROFITABILI
Page 207: Chapter 10 WHY OYSTERCATCHERS HAEMA
Page 210 and 211: 2 4 6 8 10 time on feeding area (h)
Page 212 and 213: 80- 60- o 80 60- 40- 20- INTAKE RAT
Page 214 and 215: est of bod\ behind: an estimated 22
Page 216 and 217: 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
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1000 r 1 II" 1 - r^Jan'80 PREDICTIN
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PREDICTING SEASONAL AND ANNUAL FLUC
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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
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lion of Mussels Mytilus edulis hy O
Page 381 and 382:
lulal Dal esiuanes: a comparison of
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