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INTAKE RATE AND PROCESSING RATE IN OYSTERCATCHER no pur*) month age free > flW BW K DU Ll Q UQ UQ, touts, 1 Oi 6 1 -2.25 518 33.8 20.7 700 0.85 59/5 640 Ens et ul. unpubl. .7 Or '• 4d 1 (6 2 Jin 796 677 till Hulscher 1974 1 Or '• 468 36.2 22.17 796 0.85 677 677 Hulscher 1974 A Or 7 474 ::v 876 0.85 744 744 Hulscher 1974 5 Or I. 42d 24.4 22.0 5.16 0.85 156 Swennen el nl. 1989 t. i , . 12 6.3 444 29.6 22.0 652 0.85 554 442 Sweanetseial 1989 7 i , < 12 i'.'s 450 37,8 22.0 832 0.85 707 595 Swennen
INTAKE RATE AND PROCESSING RATE IN OYSTERCATCHER Tabic 1. Daily ciiiiMiiiipiion (g AFDW) .incl body weighl Oystercatchers feeding on Cockles (Or), Mussels {Myt), commercial food pellets (pd), Si rnhii ularia i Sci i or larvae of Tipula (77/>). Source numbers (used in Pig. 3) and sources are given in ihe lirsi and last column. All birds were adults except one I -y ear and lour 3- OM bud'- (See column 'age"). All birds were held in captivity, bin studies marked wuh I m column 'tree' were free-living birds. All dala were collected in iherinoneuiral conditions, except loin and two birds held al an average air temperalure ol 6 5 and 6.3 ( column 'T'l. Body weight was constant in all studies over the periods concerned, bin decreased in study I (18 g in 8 days I. 23 1511 g in 26 day si. 28 (19 gin 30 days), and increased in Stud) 26(38 g bl 26 daysi. 27 124 g in 28 da] s). 29(13 g in 30 daysi and 30134 g in 34 days); column'BW ' gives weight change (gdaj ') Change in bod) weighl was unknown in field studies 36 and 38. but assumed to be constant Average body weight tg. column "BW") and month of observation are indicaled. Body weight was not known foi the days of observation in field study 36 and 38. but assumed lo be equal to the average weighl of the buds of the same sev. such as measured in oilier birds in Ihe same lime ot Ihe year and the same site. Columns 'g', 'kJ' and 'kJQ' give total daily coiisiiniplioii in trams ot gross \i i.ivv (gi. grossenergj ik.li and metabolized energy ik.li. respectively. Kersten & Piersma 11987) found in pellets 22.8 kJ g : fresh weighl being equivalent to 25.8 Id g"' AFDW. Goede (1993 25.1 kJ g ' AFDW Ibrdifferenl kind ol food pellets, BM>& lieimiilh I unpubl. I 19.9 kJ in ihe pellets they used. Heppleston (1971) 22.56 U g' 1 AFDW in Mussels. Merck (1983)20.7 and 21.9Ug" 1 AFDW in Cockles and Mussels, icspcelively. laken hv the buds studied by Ens (unpubl.), Blomert tt /wan- itinpuhl.i 24.5 U in Leathcriackeis in the same area where Ens collected his data (same month but later years). Zwarts I unpubl. I 22.2 U for Scnihieularia laken b) the bird studied by Blomen «•; al. (19831, and /warts & Blomert (1996) 22.9 kJ for Lealherjackels in April, ll is assumed that in the remaining five Studies the average energy contenl of Mussels was 2' kJ and kles 22 kJ g ' AFDW; column xkJ' gives ihe average energy content (kJ g ' AFDW; printed in italics if estimated). Column 'Q' gives the digestibility and 'kJQ ' the metabolized energy consumption ikJQl corrected for weight change and thermoregulation costs (see text). Each mcasurcincni concerns an individual bird, except Kersten A: Piersma 11987) and Goede (1993) whose measurements averaged 6 and 12 birds, respectively. Studies 32 lo 34 concern ihe same siv individuals being weighed each week Alter a selection was made of weeks with a temperature > 10 C and constant body weights. Ihe average consumption was calculated separately for three categories ol body weight 27; (1996) observed some breeding pairs from sunrise un- til sunset in April, in the week before egg-laying, and measured prey fragments in the droppings to recon- .i.n.i prey weights. Second, ii is possible to tstimate nocturnal fcxxl consumption in nesting birds from weight changes recorded on an clccinunc balance placed under the nest (Kersten & Visser 1996b. Ens. Dirksen. Nieuwenhuis & Smit unpubl. and Exo & Scheiffarth unpubl.). The relation between weight change and consumption was calibrated by comparing weighl changes to measured food consumption during ihc day. Compared to these few field Studies, many studies have measured daily consumption in captive buds (Table 1). With daily, consumption expressed as AFDW. the variation is large. The average gross con sumption is 323 g AFDW with a SD of 5.1 g, or 15.8% of the mean. This large variation is not due lo daily variation in consumption, since the data in Table 1 for captive birds all refer to studies that averaged the consumption over longer periods, and in some cases over several individuals. We therefore first investigate to what extent this variation was due to differences in i I i energy contenl of ihe prey. (2) digesiihilnv ol ihc prey, (3) costs of thermoregulation, (4) weight changes, (5) body weight. (6) activity costs. (7) age and (8) season. This will then allow us to assess whether a difference in food consumption occurs be tween captive and free-living birds (1) Energy content of the prey The captive Oyster catchers were fed artificial food pellets. Cockles or Mussels. The four field studies refer to breeding birds feeding mainly on Cockles (Ens et al. unpubl.) and Lealherjackels iZwarts & Blomen 1996, Ens et al. un publ.) and to a non-breeding bird feeding on Scrobicu laria (Blomen et al. 1983). As different prey types contain different amounts of energy, this diversity of food types makes it likelv lhat the variation in daily consumption would be less if it was expressed as gross energy intake. Hulscher 11974) found thai three Oys- letcatchers alternately offered Cockles and Mussels, consumed, on average, per day 37.4 g AFDW if Cock les were taken, but 33.2 g, or 11*36 less, if their food was Mussels. The energy content of both prey was not measured, but other studies have found that the energy content of Mussels is 5-1095 higher than that of Cock les iChambcrs & Milne 1979. Merck 1983. Zwarts &
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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
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
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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 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
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Page 230 and 231: Introduction PREDICTING SEASONAL AN
Page 232 and 233: PREDICTING SEASONAL AND ANNUAL FLUC
Page 240 and 241: 1000 r 1 II" 1 - r^Jan'80 PREDICTIN
Page 252 and 253: IOO BO 60 40 20 0 PREDICTING SEASON
Page 265 and 266: 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
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Pekkarinen M. 1984. Regeneration of
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lion of Mussels Mytilus edulis hy O
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lulal Dal esiuanes: a comparison of
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