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50 OOF 310.00 I 5.00 ^ 1.00 3=" 0.50 g> 1 ° 0.10lr •5 0.05 0.01 - FEEDING RADIUS, BURYING DEPTH AND SIPHON SIZE Scrobicularia plana Macoma balihica 10 15 20 25 30 40 shell length (mm) 5.00- 5 10 15 20 shell length (mm) Ug. 3. Siphon weight (mg AFDW)ol A. Scrobicularia m = I121 and B. Macoma (n = 741 in June (O) and October 1992 (•>. The upper line and SJ nibols reler to the total weighl. The grey fields indicate Ihe range ol siphon weights measured in the study area nui several years (from Zwarts A: Wanink 1989). The lower line and symbols give the total siphon weighl divided by siphon length, calculated from dala given in I ig- I and 2. siphon measured 8.5 cm. below the maximum of 11 cm and 11.5 cm found by Kamemians & Huitema (1994) and Pekkarinen (1984). respectively lor Macoma of similar size. The siphons of Scrobicularia and Macoma were relatively heavy in June and October 1992. compared to the long-term average for the same months dig. 3), but the trends are similar: in boih species, siphon weight is an allomeiric function of shell si/e. although the slope in Macoma is much lower than in Scrobicularia. Siphon cropping, feeding radius and bury ing depth There was little variation over time in the burying depth of the individual bivalves held in containers, but their feeding radius did vary. As an example. Fig. 4 shows the depth and radius measurements for two Scrobicularia and two Macoma. Simulated siphon cropping reduced the feeding radius, but did not cause a change in burying depth. Deposit feeding continued after the siphon top was lost, as was also observed by Hodgson (1982b) and de Vlas (1985): the wounded 118 siphon heals very quickly (Hodgson 1981). An average of 10'. of the siphon weight of Scrobicularia was removed and accounted completely for the smaller feeding radius. On average. Macoma (11 animals) lost 18'' of ihe siphon weight, and the average siphon was shortened by I29f or 6 mm. The radius decreased by an even greater amount (38% or 10 mm) because, contrary to expectation, siphon cropping resulted in Macoma burying themselves more deeply i4 mm or 21%). The contrary result was found in the field experiment. All Macoma had been buried by us at the same depth of 3 cm. The 44 individuals from which 20 to IsY'c ol the siphon had been removed were found ihe next day al a depth of 1.4 cm and so had reduced their depth hy 1.6 cm (SE = 0.1 cm). The 17 controls from which no siphon tissue had been removed had also moved closer to the surface, but only by 0.7 cm (SE = 0.2 cm). As the burying depth of both groups did not change over the following days, we calculated the average burying depth over this period for each individual and related this average lo the weight of the remaining siphon and to the cut part of the siphon. Heavily cropped animals moved nearer to the surface
shell sue: 32.4 mm siphon; 125-r.ll.9mg 6 7 day FEEDING RADIUS, BURYING DEPTH AND SIPHON SIZE Scrobicularia plana Macoma balthlca shell size: 296 mm slplw 13.3-.12.I mg 6 7 8 day 8 7 6 4 3 2 shell sue. 18 7 mm U siphon: 18-*1.3mg 1 - 6 7 day shell size: 186 mm siphon. 1.8-.2.2 8 5 6 7 8 day Fig, 4. Siphon length lem) ol 2 Scrobicularia and 2 Macoma measured from 5 days lo » days after burial. Shell size, siphon weight (AFDW) before and after cropping and lime of cropping I depth increased with the weight of the remaining siphon and. as Fig. 5 shows, the relationship between siphon weight and depth was similar for the cropped animals and the controls. Sta- o. & o £ 3 0 0.5 1.0 1.5 2.0 2.5 siphon weight (mg) Fig. 5. Burying depth (cm) as a function of siphon weight of Ma coma (16-17 mm) on a mudflat in May 1986 (n = 61). Except 17 controls, between 20 and 70% of the siphon weigh! has been re moved shortly before ihc depth measurements were done. 119 listical analyses confirmed that burying depths were highly correlated to the weight of the remaining siphon and that the weight of the amount thai had been cut oil did not add significantly to the explained variance. Siphon length and siphon weight Siphon length was 0.2-0.5 cm in Macoma and 0.5-2.0 cm in Scrobit tilaria after the siphons had been cut olT in the animals killed in boiling water. These ranges correspond well wilh the measurements of Hodgson & Trueman (1981) and Pekkarinen (1984). In both species, the length of the dissected siphons, as well as the weight per cm of siphon, was highly correlated with shell length (Table 1). Also, the relationship between the dissected lengih and the maximum length of the extended siphon, measured in the same (still living) Scrobicularia. was highly significant (r = 0.64. p < 0.0001). The extended siphons were ten times as long as the dissected siphons, as also found by Hodgson & Trueman (1981). To investigate the relationship between siphon weight and siphon length independently of shell si/e. dissected siphon lengths and siphon weights were expressed as deviation from the average values ot the corresponding si/e classes, using regression equations given in Table I. The relation between siphon weight and dissected siphon length was DO) linear bin curvilinear (Fig. 6).
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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
Page 67 and 68: Tahle 2. The intake rate ol < lyste
Page 69 and 70: * ' % -. . ; a X - . - * • ^ •
Page 71 and 72: (Zwarts & Wanink 1989). In quiet we
Page 73 and 74: general law relating handling time
Page 75 and 76: nearly twice as much time (0.79 s).
Page 77 and 78: 4 5 6 7 8 9 size class of Corophium
Page 79 and 80: and annually. Second, the lower siz
Page 81 and 82: Prey switching Waders feeding on ti
Page 83 and 84: autumn and spring, and the contrary
Page 85 and 86: where they switch to surface-living
Page 87 and 88: Chapter 3 BURYING DEPTH OF THE BENT
Page 89 and 90: DEPTH AND SIPHON CROPPING IN SCROBI
Page 91 and 92: I DEPTH AND SIPHON CROPPING IN SCRO
Page 93 and 94: DEPTH AND SIPHON CROPPING IN SCROBI
Page 95 and 96: Table 3. Three-Way analysis Of vari
Page 97: Chapter 4 SIPHON SIZE AND BURYING D
Page 100 and 101: 15 20 size (mm) Fig. 3. Cerasioderm
Page 102 and 103: 10 size (mm) SIPHON SIZE AND DEPTH
Page 104 and 105: o, 7 01 5 | * CL 5- SIPHON SIZE AND
Page 106 and 107: 4 Q) Si •a a. 16- 20- A predator:
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
Page 116 and 117: surface in die containers was varie
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.
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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
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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
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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
Page 367 and 368:
BreyT. 1989. Der Einfluss physikali
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latie tol chironoiiiiilen en de wai
Page 371 and 372:
huch der Vogel Milteleuropas, Band
Page 373 and 374:
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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