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Fig. 5. Scrobicularia plana. Size classes selected hv Oystercatch ers i shaded I compared to ihc size classes in the prey population (solid line): A. Total prev popu lation* B. Prey population in up per 6 cm (Fig. I); C Prev popu lation in upper 6 cm correcled foi 'effective touch area' and so actually encountered liable I i (Habekotte 1987). Fig. 6. Mya arenaria Size classes -elected by Oystercatch ers (Shaded) compared to lhesi/c classes in the prev population (solid line): A. Total prey popu lation: li. Prey population in up- pet
PREY SIZE SELECTION AND INTAKE RATE 50 60 10 20 length ol Mytilus (mm) Fig. 7. Mytilus ediilis. Si/e classes selected by Oystercatchers (shadedI compared 10 the si/e classes in Ihe prey population (solid line): A. total prej population: B. prey population corrected for 'effective touch area' (i.e. squared lengthi and so actually encountered. The data are from 9 studies vv here Oystercatchers used the stabbine. technique to open Mussels: Blomert et al (1983). Hulscher (unpubl.). Koene (1978), Ens & Ainu- (1996b), /wans ,VJ Drent 119811. Zwarts lunpubt.). captive Oystercatchers were able to eat these size classes when the prey were buried jusl beneath the surface (Zwarts & Wanink 1984). Cerastoderma edule Oystercatchers feeding on Cockles either make distinct pecks or move the bill through the substrate (Hulscher 1996). Pecking Oystercatchers taking Cockles use visual cues and do not peck at random (Hulscher 1976). This limits the validity of the random touch model even though the effective touch area (Tahle 1) correctly measures the expected encounter rate. When the bill makes straight furrows through the mud. another random touch model is more appropriate (Hulscher 1976). Oystercatchers do not take first year Cockles less than 10 mm long, when older Cockles. 20 lo 40 mm long, are available (Drinnan 1957. Brown and O'Connor 1974. (ioss-Cusiard ei al. 1977a. Sutherland 1982c. Triplet 1989b. Hulscher unpubl.). When only first-year Cockles are present. Oystercaicliers may feed on them (Meire 1996b. Zwarts el al. 1996h. Piersma unpubl.). bui this rarely occurs. When only second year, and older. Cockles are available, there is a reasonable coincidence between the obsened size selection and the selection predicted on the basis of random searching (Hulscher 1976. Leopold et al 1989). 161 Mytilus ediilis Oystercatchers use three techniques to open Mussels (Hulscher 1996). Briefly, ventral hammerers tear the Mussel from the bed. lum it over and liaimiiei a hole on the weak ventral side (Norton-Griffiths 1967). Dorsal hammerers attack the Mussel in situ on its dorsal side (Ens 1982). while stabbers stab, or force. Ihe bill between the valves. Each technique requires different measurements to define the fraction of prey actually available to Oystercatchers Stabbing Oystercatchers reject Mussels smaller than 20 to 25 mm long but take all larger size classes (Fig. 7A). Mussels larger than the apparent lower threshold of 20 to 25 mm are taken in proportions thai conform to the assumption lhat the likelihood of a Mussel being attacked is proportional to iis surface area. i.e. length squared (Fig. 7B). However, the rejection threshold differs between studies. When Mussels about 50 mm long are numerous, slabbing Oystercatchers may even reject Mussels as long as 40 mm (Zwarts & Drent 1981). Hammering Oystercatchers reject ihiek-shelled Mussels covered by barnacles (Durell & Goss-Custard 1984. Meire & Ervynck 1986. Caj lord & Goss-Custard 1990). This affects the frequency distribution of the si/e classes actually available to hammerers, since the larger Mussels are often encrusted by barnad.-
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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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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
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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
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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 145 and 146: prey density II III Fig. 12. Freque
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 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
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
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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
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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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