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$Wetenschap - \Nijverheid- Handel$

PREY DEPLETION BY OYSTERCATCHER AND CURLEW T-S*I 1 r?p-r-o-ro-i 1 1— —r-*Tf i 1 1 rr- 0 1 ^ 3 4 5 6 7 8 9 10 0 1 2 3 4 5 6 7 8 9 10 size of Mya arenaria (cm) Fig, 2. A. Si/e selection by Oystercatcher (left) and Curlew (right), preying on clams ('.; frequence distribution per 5 nun class; .ample si/c indicated). Clams ealeii hy free-living Oystercalchers in Octobcr-Novemher I9K0 or Curlews in Augusl-lVcemher 1978 are compared to the clam population on oiler in the Moddergat area for Oystercatchers and in the Nes area foi Cuilews. The righl panel shows ihe prey selection hy a single colour-handed Curlew (20Y): the size has heen derived from (he known relationship between handling time and weighl (and thus size) of the clams. B. Risk to a clam of being taken, relative to ihe maximal predaiion risk ol a single si/e class The maximal risk is set to I (Oys ieicalchei: clam si/e 3-4 cm. Curlew: clam si/e 4-5 cm). The relative risk is derived Irom the data given in Ihe upper panel. The solid triangle denotes the predicted lower limit and Ihe open triangle ihe mosi profitable si/e class (see lie. 11. did nol take all the llesh from ihe shells. In man\ cases the) pulled out the siphon, together with the greater part of the body, in one jerk. On average 22% of the llesh remained in the shell and the flesh taken averaged 51 mg ash-free dry weight. The mean handling time was 5.82 s. so the average yield during handling was 8.74 mg/s (open square in Fig. IC). This field estimate is quite close to the peifonnance curve ol" die captive Oystercatcher. Since free-living Oystercalchers devote 30.3*3S "I (heir feeding time to handling the clams (the other 69JVr being spent in searching for prey), the average rate of intake of biomass amounted to 0.303 x 8.74 = 2.65 mg/s (shaded block in Fig. IC). The theory predicts that all prey sizes yielding a lower rate of biomass intake would be ignored. The smallest clam given to 338 the captive bird was 22 mm. The handling efficiency for this is still above the predicted lower threshold. For clams between 20 and 40 mm there is a linear relationship between yield and shell size. Extrapolating the line downwards, we would expect that clams of |7.3 mm and smaller should be rejected, which fits well with the observed threshold in the free-living Oystercalchers ll-'ig. 2). The clam is also an important prey for Curlews, but the threshold size required for acceptance is higher. For this species we measured the profitability of different shell si/cs I'm licc-lniiig Curlews. It was easy to measure the handling time but impossible to estimate directly ihe size of the shells taken, because a Curlew pulls the siphon and pieces of flesh out of the shell, from below the mud surface. It was possible, however.
to locate the clams after they had been eaten, for a Curlew makes a small crater while handling the prev. We were able to locate the clams seen to be taken in relation to a grid of theosands of numbered polei, •e;\ i . rated from each other by a few metres on the feeding area. After an observation period, during which we timed the handling of the clams being eaten and noted their positions, we searched the different craters. To PREY DEPLETION BY OYSTERCATCHER AND CURLEW -i 1 r 3 4 5 6 size of Mya arenaria in cm calculate the yield for the Curlews, the flesh which remained in the shell was weighed and subtracted from an estimated total flesh weight, derived from a weight/leagtfa relationship. Figure ! shows ihe b dling time and the profitability as a funelion of the shell size for a single colour-handed I urlew (called 20Y). which fortunately fed near one of our observation towers and has done so for five years. As Fig. 1 Fig. 3. Frequency distribution of depth of clams per size class m-4. 5-9 mm. etc.). The mean and the number of clams dug out are indicated. With the aid of grey bars ihe pan of die clams being taken by Oystercatchers and Curlews are shown The nisei figure shows the accessible percentage per si/e class lor Ossiercatcliers (upper 7 cm of the substrate), and formate and female Curlews (upper 12 and 14 cm. respectively). 339
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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
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Table I. Results of five one way an
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Table 2. Results of eight iwo-wav a
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prey density II III Fig. 12. Freque
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PREY SIZE SELECTION AND INTAKE RATE
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Predicted 'passive size selection'
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lig. 2. Larger Mussels are less ava
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Fig. 5. Scrobicularia plana. Size c
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and maiiv are too thick-shelled to
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The measurements of handling time i
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1 2 3 4 5 6 7 probing depth (cm PRE
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valves may vary by a factor of two
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optimal foraging model, the minimum
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their gut is full? Do they reduce t
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PREY PROFITABILITY AND INTAKE RATE
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catchers to take only certain prey
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licult error of estimate arose if p
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Counts of feeding and non-feeding b
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20 30 40 50 shell length (mm) PREY
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Nereis Arenicola tipuia earthwo'm M
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take rate. We might therefore expec
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prey species, using parallel slopes
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5.0 4.0 1-3.0 a & • % * • * •
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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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• ' • 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
Page 283 and 284: Chapter 13 ANNUAL AND SEASONAL VARI
Page 285 and 286: VARIATION IN FOOD SUPPLY OF KNOT AN
Page 287 and 288: Two sites (N and M in Fig. 2) were
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Page 293 and 294: July ' Aug ' Sept Fig. 9. Proportio
Page 295 and 296: available. There must, however, be
Page 297 and 298: Chapter 14 SEASONAL TREND IN BURROW
Page 299 and 300: BURROWING AND FEEDING IN NEREIS SEA
Page 301 and 302: Table 2. Results of a 2-way analysi
Page 303 and 304: June 1981 June 1982 is * N.MUD •
Page 305 and 306: 8 10 I 12 JZ 5. -g 1*» •e o i 16
Page 307 and 308: 6 - n=!080 5 • g 4 CP > i 3 CO CD
Page 309 and 310: 1985) and Curlew (/wails ,v, Lsseli
Page 311: Chapter 15 VERSATILITY OF MALE CURL
Page 314 and 315: Smid! 1951. Muus 1967, Wolff 1973,
Page 316 and 317: 0.6 0.8 1.0 1.2 1.4 1.6 jaw lengih
Page 318 and 319: Na oi both Nrieck Fig. 7. Numenius
Page 320 and 321: 6 8 10 12 14 16 18 worm length (cm)
Page 322 and 323: too (Fig. 11 A). Indeed, the averag
Page 324 and 325: VERSATILITY OF CURLEWS FEEDING ON N
Page 326 and 327: total time spent al the surface. Th
Page 328 and 329: 2 4 . • 2.2 • 30 .-.2.0 to Q. 1
Page 331 and 332: PREY DEPLETION BY OYSTERCATCHER AND
Page 333: the rule: the observed lower limit
Page 337 and 338: Curlew, by bury ing some hundreds o
Page 339 and 340: PREY DEPLETION BY OYSTERCATCHER AND
Page 341 and 342: SAMENVATTING 345
Page 343 and 344: Voorgeschiedenis In 1960 verscheen
Page 345 and 346: maken. Als gebied A een grotere voe
Page 347 and 348: omdat ze nog vrijwel niets wegen. l
Page 349 and 350: kunnen opzuigen. of diep leven en z
Page 351 and 352: van de uitgerekte sifo over het wad
Page 353 and 354: het toen niet gemakkelijk hebben ge
Page 355 and 356: doende nonnetjes van 10 tot 15 mm l
Page 357 and 358: aangevoerde voedsel en de wulp past
Page 359 and 360: zijn dan twee jaar en wulpen geen s
Page 361 and 362: was dan ook dank/ij de inzet van al
Page 363 and 364: REFERENCES 367
Page 365 and 366: Allen RL. 1983. Feeding behaviour o
Page 367 and 368: BreyT. 1989. Der Einfluss physikali
Page 369 and 370: latie tol chironoiiiiilen en de wai
Page 371 and 372: huch der Vogel Milteleuropas, Band
Page 373 and 374: llolmann II. & H. Huerschelmann 196
Page 375 and 376: 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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