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Wanink 1993). The energy content of the food offered has been determined in 8 of ihe 13 sludies and was estimated by us for the remaining ones (Table I). The daily consumption of Oystercatchers averaged for all studies is 728 kJ (SD 103); SD as percentage of the mean is 14.1*36 and thus marginally smaller than the variation in the daily AFDW consumption. (2) Digestibility of the prey A further reduction in the variation may occur were the digestibility of the food to be known so thai the daily metabolizable energy could be calculated. Digestibility in Oystercatchers feeding on Mussels was 85'< of the energy (Speakman 1987. Kersicn & Visser 1996a). whereas it varies between 659! and 8991 in various types of food pellet (Kersten & Piersma 1987. Exo & Freimiith unpubl). Even though a low digestibility might be expected for Leatherjackets because this prey has a thick skin. 83 to 89% of the energy is actually metabolized (Zwarts & Blomen 1996). The metabolized energy consumption. averaged for all studies, amounts to 605 kJ per day on average (SD = 93; relative SD = 15.4%). Thus, in contrast to expectation, the variation in consumption did not decrease when expressed as net, rather than gross. energy. (3) Thermoregulation The air temperature in most studies was above 10 °C. the critical temperature below which the costs of thermoregulation increase (Kersten & Piersma 1987). However, two Studies held birds at average temperatures of about 6 °C. The extra amount of energy needed to meet these additional thermoregulation costs is estimated to be 30 kJ for each °C below 10 C. using the regression equation and conversion factors given by Kersten & Piersma (1987). The thermoregulation costs of waders along the shore are more effected by wind force than by temperature alone iWieisma & Piersma 1994). The captive birds lived in sheltered cages, however, whereas the data for free-living birds were collected at air temperatures of > 15 °C. Hence there is no need to estimate the extra COStS due to wind flow. (4) Gaining or losing body weight Another source of variation is whether birds were changing body weight. However, body weight remained constant in most of the experiments, the exceptions being indicated in Table 1. We assume that if Oystercatchers gain, or lose. 1 g fresh body weighl per day. their net energy intake would be 20 kJ above, or below, the energy consump- INTAKE RATE AND PROCESSING RATE IN OYSTERCATCHER 222 460 480 body weight (g) rig. .1. The dailv consumption IkJ metabolized energy I as a func tion of body weighl in captive and free-living Oystercalchers ac cording to several dala sources given in Table I. The digit codes in ihe figure correspond with the source numbers in Table I. The grey field indicates the variation in daily energy expenditure of adult birds during the breeding season I Kersten I'796: Table S). The daily eonsiiiiipiinn was measured al constant hixly weight and under ther- monculral conditions, and it Ihis was mu so. a correction was made (see levl and Tahle I). lion required to keep their body weighl constant. Oystercaiclieis are able lo keep their body weight constant at a daily gross consumption of 36 g and a net consumption of 670 kJ (see below). They lose 30 g a day if they take no food at all (Kersten & Visser 1996b). Hence, daily fcxxl consumption (C, AFDW) is a function of ihe daily change in body weight (AW. g): C = 36-1.2 AW. A slope of 1.2 g AFDW was found indeed in captive ()v stercatchers by Kersten & Piersma 11987). After correction for weight changes (20 kJ for each gram change of body weight) and costs of thermoregulation (30 kJ for each degree below 10 °C). the maintenance metabolism in the birds amounts to. on average. 58S kJ day' (SD=85). The coefficient of variation is 14.5%, and thus still quite large. (5) The effect of body weight Body weight explains a
significant part of the variation in daily energy intake. The correlation of the linear regression is +0.59 and +0.61 on a log-log scale (Fig. 3) wilh an exponent of 1.49 (SE =» 0.32). The SD of the residuals from the regression line shown in Fig. 3 is 69. or still 11.7*96 of the average consumption. Ihe elleci ol the three remaining variables -activity costs, age and season- has been investigated after removing the effect of body weight hv analysing the residuals. (6) Activity costs The costs of feeding might vary between the studies, being higher for free-living birds (Blomert el al. 1983, Zwarts & Blomert 1996. Ens el al. unpubl.) than for captive birds. Within the captive ? INTAKE RATE AND PROCESSING RATE IN OYSTERCATCHER digestive bottleneck (CIRmsx) • required il feeding restricted to one period a day • ••Trr.. • • • • • birds, the feeding costs might differ too. being high it the birds had to feed on an artificial cockle bank (Swennen et al. 1989) or a mussel bank (Koene 1978). and km if the birds were offered opened bivalves illeppleston 1971. Hulscher 1974 & unpubl.) or pellets (Kersten & Piersma 1987, Goede L993, Bxo & Freimiilh unpubl.). Although the energy expenditure has not been measured, the possible costs of feeding might be derived from an increase in the metabolized energy consumption. However, ihc daily consumption did not differ among the four categories of studies distinguished (p = 0.811. nor when free-living and captive birds were compared (p = 0.89). 8 10 12 14 16 time spent on feeding area (h) digestive bottleneck (ClfWl 18 22 24 Fig. 4. A. Crude iniake rate (mg AFDW" s ' i as,, function of the time spent on the feeding area. A selection was made of the studies summarized in Rg. 2A. B and C: Zn = 370 studies. One curved line shows the highest potable crude intake rale such as determined by the digestive system (CIR^: Fig. I). The other line shows the iniake rale required to keep their body weight constant, assuming thai feeding is resincted to one feeding period a day. B. Average deviation of the crude iniake rate from C1R tset to IOO', I or Irom the required crude iniake rale daily feeding period (calculated from the dala given in panel A i: number of cases indicated. 223
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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
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 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 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
Page 267 and 268: 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
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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