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

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1 2 3 4 5 6 7 probing depth (cm PREY SIZE SELECTION AND INTAKE RATE 350 prey nv 2 0 1 2 3 4 5 6 7 maximal prey depth accepted (cm) Fig. 12. Experiment toshow why an Ov siercatchei ignored deep, less profitable prey when the intake rale increased due to a high prev density V. Tune needed to handle Scrobicularia 37-38 mm long which were laken from different depths (s ± SE). B. Time needed io probe to different depths (s ± SE). C. Predicted feeding rate (Scrobicularia min ') at two prey densiiies when an Oystercatcher took prey from the upper I. 2. ... 7 cm of the substrate. Actual observed depth selection is indicated vv ith horizontal bars. As predicted, the bird took prey from all depths when the prey density was low and only shallow prey when the prey density was high However, the bird did this al a much higher rate than predicted (explanation given in text). Data of Wanink & Zwarts (Iis s > nomics of foraging are being calculated. It has been shown experimentally that a captive Oystercatcher decreased its probing depth from 7 to 3 cm when the density of the prev on offer. Scrobicularia 36-37 mm long, increased from 24 to 350 prey nr 1 (Wanink & Zwarts 1985). It took more time to handle deep-living prey (Fig. I2A). hence prey profitability decreased with depth. Moreover, it also took more time in the first place to locate a prey at greater depths (Fig. I2B). The encounter rate, defined in optimal foraging models as the inverse of the searching time, for prey at different depths could be calculated from the effective touch area and the probing time at each probing depth. Since the encounter rate and the handling time were both known for each depth class, the optimal set of depth classes, which should be included in the diet to maximize the intake rate, could be predicted exactly with a multi-species functional response equation (Charnov 1976) (Fig. 12C). The depth selection made 166 by the bird was very close to that which was predicted. The Oystercatcher took prey from all depths when the density was low but rejected the deep, less profitable prey when prey density was high: by doing so, it increased its intake rate at high prey density by eating only the most profitable, shallow prey. It may be thought from Fig. 12C that the bird could have done slightly better by selecting prey only from the upper 1 cm, and not from the upper 3 cm. as it actually did. But. in fact, the Oystercatcher did even better than predicted by using a second selection criterion, as will be explained in the next section. The conclusion from this experiment is that Oystercatchers are indeed able to vary the rate at which they encounter different prey types and. in doing so, increase their intake rate. Rejection of prey to increase intake rate The previous section showed that Oystercatchers are able to adjust their searching behaviour in order to in-
crease their encounter rate with more profitable prey. The next decision Oystercatchers have to make is which of the encountered prey they should lake and which ihey should ignore. As noted above, the captive Oystercatcher studied by Wanink & Zwarts (1985) was able to attain an intake rate 50*31 above the predicted rate when prey density was high (Fig. 12C). Their explanation for this was thai, at the high prey density, the bird only took prev from the upper 3 cm thai were gaping and so could be stabbed immediately. As a result, the prey were opened and the llesh swallowed in less than 15 s. nearly twice as quickly as when a typical prey from the upper 3 cm was taken (Fig. 12A). The hypothesis that Oystercatchers mav ignore closed, and thus less profitable, bivalves had already been proposed by Hulscher (1976) who observed that Oystercatchers spent less time handling Cerastoderma when prey densiiv increased. By rejecting closed bivalves when prey are abundant, Oystercatch- 50- 40- i/i "5 I 20 E 3 C 10(- PREY SIZE SELECTION AND INTAKE RATE I other species •uyi I Scrobicularia | Macoma "JrVyWus H Cerastoderma fit 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 intake rate (mg-s-") Fig. 13. Frequency dislribulion of Intake i.ites i mg ash tree dry llesh - feeding) measured in 197 studies, given •eparaiely for five bivalve species, data for -even other prev (pedes are lumped. The souices for the live bivalve species are given in Ihe legend to I ig. 14. Other sources: Ragworm Nereis diversicolor. Boates & (loss Cus tard 11989k Bunskoeke elal. (I996). Durell
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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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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 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 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
Page 207: Chapter 10 WHY OYSTERCATCHERS HAEMA
Page 210 and 211: 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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