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

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(7) Age All studies dealt with adult birds, but Heppleston (1971) worked with a yearling and Exo & Freimiith (unpubl.) with two subadults three years old. The few dala available suggest no reason to assume that the consumption is different for the age classes w hen birds of similar body weight were compared (p = 0.87). (8) Season There is also no seasonal variation in the consumption al thermoneutralily (p - 0.31). In conclusion, the daily consumption of Oyster catchers with constant body weight and living in thermoneutral conditions greatly depends on their body weight but not on whether they live in captivity or in the wild. Oystercatchers in Ihe wild weigh 520 g during most months of the year. From Fig. 3, their daily net energy intake can be estimated at 672 kJ, which is equivalent to a gross consumption of 790 kJ or 36 g AFDW. Crude intake rate and the digestive constraint Although the amount of focxj consumed increases wilh the amounl of time spent on the feeding area (Fig. 2), ihe rate at which fcxxl is taken nonetheless decreases. This is illustrated in Fig. 4A, where the crude intakerales are plotted againsi feeding lime, using the data from Figs. 2A. B and C. The curved lines in Fig. 4A show CIRm> and the required crude intake rate, assuming thai the birds need 36 g a day at thermoneuiraliiy and take all this fcxxl during one feeding pericxl a day. It is clear from Fig. 4 that, under these conditions, ihey cannot meet their daily energy requirements in less than 11 h. The highest crude iniake rate ever observed was 16 mg AFDW s' and was measured in a hungry Oystercatcher. offered opened Mussels, that fed for 13 min (Hulscher unpubl.). This bird must have filled up its digestive tract completely during this short feeding bout. The three other studies with crude intake rates exceeding 5 mg s ' concerned birds foraging for less than 30 min. Even so. these extremely high iniake raies still lie below CIRnux. But as Fig. 4A also shows, even though the observed crude intake rates decrease with the lime spent on the feeding area, they do not all fall below CIRmi>. perhaps because of errors of estimation. In fact, the observed crude iniake rales follow, on average, the ClRm.ix curve over the feeding time range of 3 to 5 h. To show this, we turned all crude iniake rates INTAKE RATE AND PROCESSING RATE IN OYSTERCATCHER 224 into deviations from predicied C3R and plotted the hourly average deviation from CIRm v againsi rime (Fig.4B). Figure 4 shows that if the birds forage less than 3 h. the CIRin.ii is so high, lhat the achieved crude iniake rale usually remains far below this maximum, ln other words, the rate at which prey are found and eaten determines the intake rate. The consumption is also usually less than CIR when the birds are able to feed s nun for longer than 11 h. because they have time enough to consume the 36 g they need. However, when low water feeding areas are exposed only for during 3-5 h. the average crude intake rate is equal to CIRmix (Fig. 4B). On these occasions, the birds consume, on average, as much food as the digestive system allows. Feeding activity and the digestive constraint What do wild Oystercatchers do if the digestiv e sv stem sets a limit lo their consumption? Do ihev Iced ai ihe low level of 0.66 mg s" 1 , set by the processing rate, throughout the feeding pericxl, or do they feed more quickly and slop feeding intermittently to resume feeding later on? The relationship between average iniake rate and feeding activity over the entire feeding period in relation to the duration of the feeding period will be analysed in the next section, using the same data as shown in Fig. 4. However, to know what birds do as their digestive tract is filling, we need data on the change in intake rate and feeding activity within the feeding pericxl. We therefore reanalysed the data of Zwarts & Drent (1981) who. over many days, counted Ihe number of feeding and non-feeding Oystercatchers on a mussel bank each quarter of an hour. We restricted Ihe analyses io counts made in late summer and autumn, since those from spring and early summer partly refer to breeding buds that visited the mussel banks during short bouts of only 1 h. Figure 5 shows that the Oystercatchers arrived on the mussel bed between 3 and 2 h before low water and left between 2h 30" and 3 h after. The average Oystercatcher was present on the mussel bank between 2h 45' before low water until 2 h 52' after low water. making a total of 5h 37". On the digestive bottleneck hypothesis, the highest possible consumption over this lime span would be 24.16 g (Fig. I) and so CTRmi> would be 1.20 mg s 1 . on average. The average feeding activity was 81%. Hence, ihe average iniake rate must
- 4 - 3 - 2 - 1 0 1 2 3 time (h relative to low water) tig. 5. Average feeding activity i'7 of Ov stercatchers feeding) OO a mussel bank over ihe low water period and (he average total nunihers ihirds ha ') al which Ihey occurred. Data of Avails Ol .£ 70 1 •2 65 60 55 50 • • • • • • • • • • • • • • • • r • * V, • • • • • c • • • • • .*< S-S-, s #•/ •
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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
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)
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 218 and 219: Wanink 1993). The energy content of
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
Page 269 and 270: 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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