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— c OJ JZ 20 10 8 6 4 2 ." • VS X A** • /,, PREY PROFITABILITY AND INTAKE RATE 0 / / / /•O a A u S ,- A/ / s • • /O V • .^VS^TA //J-^* A >fj^' • Tipu/a A 4 / ^^"A ' • Earthworm o Arenicola /x. Nereis ... .i , s , . i .... i 10 50 100 500 1000 prey weighl (mg) Kin. 7. Handling time as a function of prey weighl (mg AFDW > in earthworms tKns unpubl.). Nereis iBoale- isiaid I9S9. Em el ul. 1996a, Hulscher unpubl.I. Tipula iHloinen & Zvvans unpubl.. Ens unpubl.I and Arenicola (liunskoeke 1988 & unpubl). The handling limes of ihe four species differ sigmlic.mil> according to a covariance analysis (R 2 =0.918 for prev weight and R s =0.025 lor ihe species i. 10 50 100 500 1000 prey weight (mg) The large scalier in the profitability of armoured prey could largely be explained by the species concerned and the technique used to open them. An analysis of covariance revealed lhat the 11 prey species alone explained 39.1 '< of the variance, prey weight 15.1'.. whereas 24.11', could be allnhntcd K) both. lb visualize the differences in profitability between species, independently of prey weighl. we regressed profitability againsi prey weight for the armoured and soft-bodied prey, without distinguishing among the species, and calculated for each species the average deviation Irom ihe regression line. Fig. 9 is based upon these calculations and shows ihe average profitability per species, standardized lo a prey weighl of 200 mg. Four types ol prey can be distinguished. First, soli bodied prey taken from the surface had a profitability of 30-35 mg s'. Second, if soft-bodied prey were extracted from the substrate, their profitability was reduced to about half, as indicated for Leathcr|,ickcts, bul not shown as a separate category in Fig. 9. Third, the average profitability of bivalves living buried in the substrate was 10-15 mg s '. but was about half this value when prey had to be taken from a great depth. Fourth, hard-shelled prey found just beneath, or from the surface, were the least profitable prey (4-8 mg s '). Fig. 8. Profitability tmg s ' handling) as a t unction of prey weight (mg AFDW). given separate I v lot soft-bodied prev (same data as lig 7) and armoured prey im addition to the dala given in I-igs. 2-1. also Anadara (Swennen 1990), Lillorina (Boaies St Gott-Custard 1992), I'alclla iS.itnel 1967) and Ilea (Ens etal. 1993 & unpubl). The regression lines are shown separately for sofl-bodied and armoured prey. A multiple iion analysis revealed that non-parallel regression lines did not explain more variance than parallel ones iR = 0.51s gad 0314. respective! v i Hence a common exponent (0.421) may be used with different intercepts: 0.788 for armoured prev and 1.490 for soft-bodied prey. 188 5000
Nereis Arenicola tipuia earthwo'm Mya Macoma Scrobicularia Cerastoderma Mytilus Anadara Uca PREY PROFITABILITY AND INTAKE RATE soil 0 5 10 15 20 25 30 35 40 profitability (mgs-' handling) Fig. 9. Coinparaiive profitabilities rf diltercni prev species, calcu lated as a relative deviation from the relationship between prof itability and prey weighl (Fig. 8. using a common slope buldilferent intercepts l"t armoured and soft-bodied prey land then standardized for a prey of 200 mg. According to a one-wa) analysis ..| variance, Ihe standardized proliiahihlies difler signilicanlly between Ihe species and categories concerned (R : = 0.87. p < 0.001. n = 41X1) The values are extrapolations lor some small prey always weighing less than 21X1 mg. Of these prey, hammered bivalves were less profitable (4-6 mg s ') than those which were stabbed (6-8 mg Faking the ratio shell weight to llesh weight as a measure of the amount of armour, profitability was directly related to prey armour (Fig. 10): clearly, it was least for the most heavily armoured prey. Figures 2-10 show ihe lime actually laken to handle prey and so ignores ihc waste handling time spent on rejected prey. If waste handling times due to prey being rejected or stolen prey were included, the graph for the soft-bodied prey in Figs. 8 and 9 would not change much because few prey were iel used and waste handling time was very short (Ens et ul. 1996a). In conirasi. waste handling limes had a significant effect on piev profitability in armoured prey, such as Mussels 189 hammered on the dorsal or ventral side tMeire .V Ervynck 1986, Cayford & Goss-Custard 1990. Ens & Ailing 1996a. Meire 1996c). As a consequence, the difference in profitability between soft-bodied, and armoured prey at the surface is even larger than shown. In conclusion, prey weight varies by a factOI of 1000 whereas, over this range, handling time increases only about 100 times. The relationship between handling time and prey weight is different for the various prey species. It takes 4.4 times more time to prepare and consume the flesh of armoured prey compared with a soft-bodied prey of a similar energy value. Among the armoured prey, surface prey take more time to handle than burying species. The handling time of burying prey increases, however, if they arc laken from deep beneath the surface. Intake rate and prey weight If the time taken lo search for prey is negligible, the iniake rate during feeding is equal to the prey profitability, the iniake rale as the prey is being handled. The profitability of the prey thus sets the upper limit (0 in- •10 35 • Ne/M V/.'js *8jm 5 10 15 armature (shell/flesh weight) rnCyl=3.328-0 I06» riMiManHianiiiMi rVadantSa •• Fig. III. Profitability as a function ol ihe annum index in prey con taining 2(H) mg llesh. The corresponding shell length of ihe bivalves is unhealed The fitted curve is highly significant (r = -0.91, p = 0.00031. Profitability ol the ditleieni pie) Species KM standardized for a prey of 2IX) mg (see Fig ll. Armature index is defined as the ratio shell to flesh weighl for the size classes concerned Shell weights from Wolff el al. ' 1987), /"wans & Women | I9°2i. llesh weights from Zwarts 11991) and Zwarts & Wanink (I'W). 20
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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
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 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 183: PREY PROFITABILITY AND INTAKE RATE
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
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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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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