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

More documents

Recommendations

Info

$Wetenschap - \Nijverheid- Handel$

spend time in opening them. In contrast, soft-bodied prey are ready to eat. Ihey are also buried and must be searched for. but they are an easy prey for Oystercatchers when ihey come to the surface to feed themselves (Ragworms Nereis) or to defecate (Lugworms Arenicola). The extent to which various prey species provide a staple food for the Oystercatcher varies dramatically with season. Inland fields are heavily exploited by breeding birds in spring and summer, but only used as a supplemental food resource by mosl Ovsiercatchers in winter (Heppleston 1971. Daan & Koene 1981. Goss-Custard & Durell 1984). On the tidal Hats, Macoma is laken in early spring, whereas Nereis predominates in late spring (Bunskoeke el al. 1996). Both prey are only locally important. In contrast as the papers reviewed below show. Mussels and Cockles are universallv important winter foods. The fact that Shore Crabs are only taken in summer is easily explained by their migration to deeper water in autumn (e.g. Beukema 1991). However, (he other prev occur year-round in ihe same habitat, with many individuals growing for scv - eral years. We lake as a working hypothesis that the seasonal changes in the utilization of these prey by the Oystercatcher population are primarily due to seasonal changes in harveslability of the prey. i.e. the prey fraction lhat is both accessible and profitable (Zwarts & Blomert 1991, Zwarts & Wanink 1993). By definition, harvestability is negatively related to the effectiveness of Ihe morphological and behavioural anti-predator defenses of the prey. Since each prey species has different adaptations to reduce predation risk, we may also expect differences between prey species in the time of year when the defenses are most effective. The intake rate is defined as mg s' feeding, thus ihe quotient of weight of the prey and feeding time. Feeding time consists ol two components: searching and prey handling. Hence the intake rate is the product of two ratios: prey weight/handling time x handling time/(search + handling time). The first ratio, the intake rate during prey handling, is called the profitability. The second ratio is the relative handling time, the proportion of the feeding lime during which the bird handles the prey. PREY PROFITABILITY AND INTAKE RATE 176 ll is obvious that the iniake rate will increase when the prey are large, arc handled in a short time, and/or when the search time between prey is limited. Several studies (Hulscher 1976. 1982, Wanink & Zwarts 1985. Habekotte 1987, Goss-Custard
catchers to take only certain prey from a mixture of different size classes and prev species. Methods Studies The data presented in this paper have been taken from 57 articles. 6 student reports. 4 unpublished theses, but also from unpublished data files of Anne-Marie Blomert. Klaus-Michael Exo, Kees Hulsnmn. Cor Smit and the live authors: all sources are listed in the appendix. The studies were performed in 20 areas (Fig. 1), of which ten are siiualed in Great Britain and Northern Ireland, six in the Netherlands and one in Denmark. France. Morocco and Mauritania. All studies were done in the field on free-living Oystercatchers. except those indicated as C in column 'Cap' of the appendix which refer to caged birds. Captive birds were either taken to the mudflats where they were allowed to Iced in temporary cages (Hulscher 1976. 1982. unpubl.) or BUR = Burry Inlet CON = Conway River EXE = Exe estuary FOR = Forth estuary FRI = grassland in Friesland MOR = Moreeambe Bay 0OS = Oosterschelde esluary PAE = Frisian coast neat Paesens SCH = Frisian island Schiermonnikoog SKA E Skallingen SKO = Skokholm SOM = Baie de Somme STR = Strangford Lough TEX = Frisian island Texel TRA = Traih Melynog VLI = Frisian island Vheland WAS • Wash Bay YTH = Ythan estuary PREY PROFITABILITY AND INTAKE RATE they were offered food on artificial mudflats (e.g. Swennen et al. 1989), Captive birds thus led in an almost natural situation, hut occasionally the food supply was manipulated either bv erasins* surface tracks that might reveal the presence of ihe prey (Hulscher 1982). or by implanting prey at different depths i Wanink & Zwarts 1985. 1996). Prey size Size classes taken were known because prey remnants could be collected, and/or the prey size was estimated when ihe birds held the prey in the bill. In the latter case, bill length or the size of ihe colour ring could be used as a ruler of known si/e. Calibration experiments showed lhat observers could estimate prey size this way rather consistently (Ens 1982, Goss-Custard et al. 1987, Boates & Goss-Custard 1989. Baser al. 1996b). Such estimates were usually accurate. In others, errors could be corrected. For instance, comparison of the size frequency distribution of remnants of fiddler crabs Uca tangeri taken by Oystercatchers (Ens unpubl.) and Fig. I. Map of the study areas in NW. Europe indicated hy three letter codes [too •Old* areas vi ere situated in Africa: ihe Bay olDakhla, Morocco (formerly Western Saharal and the Banc d'Arguin. M.HIM : 177
Page 1 and 2:
WADERS AND THEIR ESTUARINE FOOD SUP
Page 3 and 4:
plia^ohi. WADERS AND THEIR ESTUARI
Page 5 and 6:
Waders and their estuarine food sup
Page 7 and 8:
WADERS AND THEIR ESTUARINE FOOD SUP
Page 10 and 11:
figuren: Dick Visser omslagfoto: Ja
Page 12 and 13:
15 Versatility of male curlews (Num
Page 15 and 16:
That science is making progress, ma
Page 17 and 18:
INTRODUCTION The remnants of brushw
Page 19 and 20:
When hcnlhic bivalves extend llien
Page 21 and 22:
the burrow depths and on the fracti
Page 23 and 24:
INTRODUCTION Ms,i invest 409 of (he
Page 25 and 26:
able lo sw itch 10 oiher prey which
Page 27 and 28:
Long-term, broadly-based research c
Page 29 and 30:
Chapter 1 SEASONAL VARIATION IN BOD
Page 31 and 32:
SEASONAL VARIATION IN BODY WEIGHT O
Page 33 and 34:
Tahle 1 Weight loss ('•- ± SE) m
Page 35 and 36:
Page 37 and 38:
Page 39 and 40:
i 60 50 40 30 20 10 0 • INFESTED
Page 41 and 42:
240- SEASONAL VARIATION IN BODY WEI
Page 43 and 44:
20 10 0 -10 -20h 2 3 4 5 6 7 8 9 se
Page 45 and 46:
a E 400 - S. plana 35 mm 320 240 16
Page 47 and 48:
Page 49 and 50:
Chapter 2 HOW THE FOOD SUPPLY HARVE
Page 51 and 52:
FOOD SUPPLY HARVESTABLE BY WADERS H
Page 53 and 54:
Methods The study sites were situat
Page 55 and 56:
less than that of bivalves, partly
Page 57 and 58:
I Fig. 3). Peak condition was reach
Page 59 and 60:
total biomass since most of those t
Page 61 and 62:
on the basis of the preceding and t
Page 63 and 64:
However, for obvious reasons, we ma
Page 65 and 66:
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
Page 112 and 113:
* ' 1 /-/ "».-^*«C
Page 114 and 115:
face and so expose themselves to a
Page 116 and 117:
surface in die containers was varie
Page 118 and 119:
50 OOF 310.00 I 5.00 ^ 1.00 3=" 0.5
Page 120 and 121:
Tahle 1. Macoma and Scrobicularia.
Page 122 and 123: siphon would not have to reach the
Page 124 and 125: known siphon weight and burying dep
Page 127 and 128: ACCESSIBLE PREY ARE OFTEN IN POOR C
Page 129 and 130: 1 2 3 4 burying depth (cm) Kin. I.
Page 131 and 132: I—1 • • : : : : ! - ! -|-r 0
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
Page 168 and 169: their gut is full? Do they reduce t
Page 171: PREY PROFITABILITY AND INTAKE RATE
Page 175 and 176: licult error of estimate arose if p
Page 177 and 178: Counts of feeding and non-feeding b
Page 179 and 180: PREY PROFITABILITY AND INTAKE RATE
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 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
Page 228 and 229:
. 1', L ! •
Page 230 and 231:
Introduction PREDICTING SEASONAL AN
Page 232 and 233:
PREDICTING SEASONAL AND ANNUAL FLUC
Page 234 and 235:
Page 236 and 237:
Page 238 and 239:
Page 240 and 241:
1000 r 1 II" 1 - r^Jan'80 PREDICTIN
Page 242 and 243:
Page 244 and 245:
Page 246 and 247:
Page 248 and 249:
Page 250 and 251:
Page 252 and 253:
IOO BO 60 40 20 0 PREDICTING SEASON
Page 254 and 255:
Page 256 and 257:
Page 258 and 259:
Page 260 and 261:
Page 262 and 263:
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.
Page 271 and 272:
fused, specimens larger than this w
Page 273 and 274:
50 100- s s I — f = S. plana, n=2
Page 275 and 276:
area is twice as large as the touch
Page 277 and 278:
10 15 lower size threshold (mm) Fig
Page 279 and 280:
lime (Hughes 1979). This would furt
Page 281 and 282:
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
Page 289 and 290:
20 30 VARIATION IN FOOD SUPPLY OF K
Page 291 and 292:
20 l i r'l ' i •o j^y^T n ^ ' " ^
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 and 334:
the rule: the observed lower limit
Page 335 and 336:
to locate the clams after they had
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
show all

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

Create successful ePaper yourself

Delete template?

Save as template?