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

Notes lo appendix:
PREY PROFITABILITY AND INTAKE RATE
1: \H)\\ ol Anuiliir.i taken was 3.1IK) me. bill 56'. of the
prey could not he eaten completely, due to klepiopamsjtism
hv oilier hird species. Since Swennen estimated thai 74:
in these case-, .ui overage. 10% of the flesh was eaten, the
weighl of the average prey laken was estimated to be 1637 76-77:
mg.
2-3: Since the birds also look Maennia and Wren, a selection
was mode of 5 nun periods during which AjWTtiCoUi was
the dominant prey.
4: Cockle height ha- been convened lo lengih using Table 5 81:
m /wails i 19911. ash assumed to he 20 r ' (being ihe average
winter level: Zwarts 1991).
5: The intake rale varied between 1.4 and 2.2. mg s ' during 82:
six different winter months. The dala were pooled since
the observation nine- were limned.
8-15: Since the birds also took Msiilus. a selection was made ,if
5 min periods with Cerastoderma as dominant prey. 83:
25: Feeding area was exposed 5 h during daylight in January:
iiii-1- equivalent to 6.5 h per low water period. Goss-Custard
(1977) noted lhat the avarage prey weight was overestimated
since small prey were probably missed and flesh 85-87:
also remained in ihe shell.
26-29: Ash assumed to be I3"3f in summer (being the average
summer value; /.warts 19911
31: The flesh remaining in the -hell has been measured 94-112:
(14.8% relative to lotal AFDW). 117-126
33-38: The same dala are given separately for individuals by
Swennen etal. (1989). 127-132
52-54: Since the birds also took Tt/iula. a selection was made of 5
min period- .luring which eanhworms were Ihc dominant 134-161:
prev.
55: It l- assumed lhat the bird- took ihe average prey present.
56: It i- assumed lhat the ash content i- 40 'he same
area in later years; Blomert & Zwarts unpubl.).
57-64: Ash of Littorina in winter is assumed lo be 10% (Chambers
& Milne 1979). 164-165
65-69: Since the birds also took Nereis, a selection was made of 5
min periods during which Macoma was ihe dominant
prey-
70: Since the birds also took Cerastoderma. a selection was
made of 5 min periods during which Macoma was the
dominant prey. 167:
71-72: The estimation of the consumption per low water feeding
period is based upon measuremenLs of the feeding rate in 182:
colour-marked non-breeding birds (study 71) and breeding
birds (study 72). but Ihc feeding activity and mean 184-191;
prey weight were based on counls and prey collection, respectively,
in which breeding and non-breeding birds
could not be distinguished. That is why a calculation of the
209
low tide consumption |41 g AFDWi would be too high for
ihe non-breeding, even if ihey remained 6 h on ihe feeding
area, since presumably iheir feeding activity would be
lower than for ihe breeding birds.
Intake rate of captive birds averaged for two experimental
conditions lera-ed and "
A pair of individually marked Oystercatchers visited tidal
mudflats adjacent lo their nesl during short feeding bouts:
Studies 76 and 77 give ihe averages for Ihe week before
and after eggs were laid, respectively: feeding role already
given hy Hulscher (1982: Kig. 2" I
Since the birds also took Macoma, a selection was made
of 5 min periods during which Nereis was ihe dominant
prey.
The birds usually only look the siphon. This partial consumption
did not cause an overcsliiiiation of the consumption,
since the llc-li taken was estimated from Ihe si/e of
the pieces of flesh extracted from the shell.
The birds look small Mya in one jerk, taking Ihe siphon
bul leaving o pan ol the body behind in the shell. When
this was imitated in the laboratory 22', of Ihe llesh remained
behind. Tin- was laken as a correction factor.
Study 85 and 86 give same data as Body 87-93 averaged
lor all months and split up for slabbers, dorsal and ventral
hammerers. Iniake rales are given hv Boatea 11988). Exposure
nine according li. Goss-Cusuud (unpubl.).
details in Cayford (1988)
Summary of Ihe data are published by Kns 11982). Ens &
(ios-Cusiard 11984), Suiherland & Ens < 1987).
Since the birds also took Cerastoderma. a selection was
made of 5 min periods with Msiilus as dominant prey.
The majority of the data arc given in Goss-Custard er al.
1984. Goss-Custard & Durell 1987 & 1988. The intake
rate- were recalculated, however, from the actual
AFDW/mussel length relationships measured mi the mussel
bed. month and year in question, whereas ihe original
paper gave siandardi/cd intakes rales
Ash assumed io be 20'. in winter. Observations were restricted
to 5 h around low water, and give according to
Hepple-lon (1971) an overesiimation when exlrapolated
to the extreme long exposure limes in October (stud)
I64i. when the birds were less active al Ihe end of the
feeding period.
Hungry, captive Oystercatchers were offered shelled
Mytilus.
The llesh remaining in the shell has been measured (7.6%
relative to lotal AFDW).
The intake rates deviates Irom those orginally published
(Zwarts & Dreni 19811. due to recalculation. Exposure
lime of ihe musselbed in May was. as in the other months.
6-6.5 h. but the watched adults were breeding birds and