WADERS (CHARADRII) AND OTHER WATERBIRDS AT LANGEBAAN LAGOON, SOUTH AFRICA, 1975–1986

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WADERS (CHARADRII) AND OTHER WATERBIRDS ATLANGEBAAN LAGOON, SOUTH AFRICA, 1975–1986L. G. Underhill aa Department of Mathematical Statistics , University of Cape Town , Rondebosch,7700, South AfricaPublished online: 11 Oct 2010.

To cite this article: L. G. Underhill (1987) WADERS (CHARADRII) AND OTHER WATERBIRDS AT LANGEBAANLAGOON, SOUTH AFRICA, 1975–1986, Ostrich: Journal of African Ornithology, 58:4, 145-155, DOI:10.1080/00306525.1987.9633896

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OSTRICH Vol. 58, No. 4

December 1987

WADERS (CHARADRII) AND OTHER WATERBIRDS AT LANGEBAAN LAGOON, SOUTH AFRICA, 1975-1986

L. G. UNDERHILL

Department of Mathematical Statistics, University of Cape Town, Rondebosch, South Africa, 7700

Received Augurt 1986

SUMMARY

UNDERHILL, L. G. 1975-1986. Osrrich

1987. Waders 58: 145-155.

(Charadrii) and other waterbirds at Lange baan Lagoon, South Africa,

Lan ebaan Lagoon was surveyed for waterbirds at midsummer and midwinter between 1975 and 1986. The med?an number of birds counted in summer was 37 500, of which 34 500 were waders (93 % of the waders bein Palaearctic migrants). Curlew Sandpiper (59,2 %), Gre Plover (10,5 %), Sanderling (8,3 %), Knot (8,1$0) and Turnstone (5,7 %) were the major com onents oJthe summer wader population. The median number of birds in winter was 10500, of which 4900 were flamingos and 4000 waders. For Palaearctic waders, the median winter population was 1 1 3 % o f the median summer population, but vaned between 2,5 % and 30,1%. For species of wader which breed in the Taimyr Peninsula, Siberia, a three-year cycle in the numbers of birds overwintering was detected, with large numbers in 1977, 1980, 1983 and 1986. Birds feeding on invertebrates consumed 126,9 kJ m-2 yr- ' , or 24 % of the total production of invertebrates. Greater Flamingos have a major impact on energy cycling at Langebaan Lagoon, accounting for 73,3 % of the winter energy consumption by the avifauna. Lan ebaan Lagoon is the most important wetland for waders in South Africa, accounting for about 10 % o!the coastal wader population of South Africa. At midsummer, about 0,5 % of the total wader population of the East Atlantic Flyway is at Langebaan La- goon, which ranks about 20th in importance for waders on the flyway.

INTRODUCTION

Langebaan Lagoon (33 S; 18 E) is a sheltered inlet from Saldanha Bay, on the Atlantic coast of the Cape Province of South Africa (Fig. 1). It is approximately 15 km long and averages 3 km wide (Day 1959). Because of its size, early descriptions of the composition of the avifauna at Langebaan Lagoon were based on surveys of small areas (Gill 1934; Liversidge et al. 1958; Pringle & Cooper 1975). A survey over four consecutive days in March 1956 was fairly comprehensive (Rudebeck 1963). It was not until 1975 that the first comprehensive and synoptic survey to count the number of birds took place. Since then there have been surveys each summer and winter. An analysis of the numbers of waders over the period 1975 to 1980 showed stable summer populations, but large year to year variations in the proportion of Palaearctic migrants that overwintered (Robertson 1981). In this paper, summer and winter counts of both waders and non-waders at Langebaan Lagoon between 1975 and 1986 are analysed.

Energy consumption by waders in relation to food supplies at Langebaan Lagoon, described for a single summer and winter by Summers (1977), is re-examined using 12 years' data. Energy consumption by non-waders is considered for the first time.

Langebaan Lagoon was proclaimed a National Park on 30 August 1985. This paper documents the significance for waders of the conservation of Lan- gebaan Lagoon in the national and international context.

METHODS

Seasons refer to the austral seasons. Langebaan Lagoon and an adjacent sandy beach facing the Atlantic Ocean (Fig. 1) were surveyed each summer (January or February) and winter (June or July) between winter 1975 and winter 1986, yield- ing census data for waders over 11 summers and 12 winters and non-waders over nine summers and 10 winters (Underhill 1986a). Both summer and winter surveys were made at a stage in the annual cycle at Langebaan' Lagoon when no known large-scale movements of birds occur (Pringle & Cooper 1975). As in Summers (1977), the summer counts have been taken as representative of the period September to April (242 days), and the winter counts refer to the period May to August (123 days). Seasonal counts by Pringle & Cooper (1975) support this assumption. Counts were made at high tide when waders congregate to roost on saltmarshes and sandspits. Up to 12 observers simul- taneously counted the birds in areas of between 50 and 100 ha each. Sanderlings fly across the Don- kergat peninsula to roost on the Atlantic beach (Pringle & Cooper 1975; Summers et al. 198%) and were counted there (Fig. 1). Because cormorants did not in general congregate to roost at high tide, counts for these species are incomplete, and they have been excluded from this analysis. Fur- ther details of the surveys are given in Summers (1977) and Robertson (1981).

To prevent very large or small counts from dominating results, medians were used in prefer- ence to means to summarize the summer and win-

145

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146 UNDERHILL: WATERBIRDS AT LANGEBAAN OSTRICH 58

FIGURE 1

The East Atlantic Flyway for waders, showing positions of major wetlands (see Table 5for names of wetlands A-Z, a-c.). Inset shows Langebaan Lagoon, southwestern Cape, South Africa.

TABLE 1 &DUN COUNTS, BIOMASS AND DAILY ENERGY EXPENDITURE OF BIRDS AT LANGEBAAN LAGOON AND ADJACENT SHORE, MID-

SUMMER AND MIDWINTER, 1975-1986

summer Winter Mass DEE Biomass DEE Biomass DEE

specjes g kJ/dsy No. kg xlWWlday No. kg x 1IY Wlday

P n L u r C t i c W d C r S T\lmstoae 117 215 1976 231.2 424.3 736 86.1 158.2 A~Mlioinurpra RingcdPlover 55 136 242 13.3 32.8 0 C-hialiCUla Sand Plover 62 146 3 0.2 0.4 0 chamddwk&naullii Grey Plover 217 313 3615 784.4 1130.1 520 112.8 162.7 PlvvioLirqvcrrprdcr M 138 20672 1 157.6 2836.1 1 132 63.4 156.2

24 62 303 7.3 24.8 3 0.1 0 2 ColidrismLucto Knot 143 243 2808 401.5 681.2 167 a 7 45.4 ColidricMwrrc

Ruft 106 202 10 1.1 2.0 0 Philomachul pugMx

% ! z r ~ E

b&p& 55 136 2847 156.6 386.3 209 11.5 28.4

L&kStlOt

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1987 UNDERHILL: WATERBIRDS AT LANGEBAAN 147

TABLE 1 (cont) Summer Winter

MESS DEE Biomass DEE Biomass DEE Species g W/day No. kg xI@kJ/day No. kg x I@ kJ/day Terek Sandpiper 75 163 78 5.8 12.8 3 0,2 0.5 Xetuucinereus Marsh Sandpiper 72 160 5 0.4 0.8 0 Tringa s t a g d i s Greenshank 200 297 443 88.6 131.8 110 22.0 32.7 TMga ncbuklricr Bar~ailedGodwit 291 374 199 57.9 74,4 32 9.3 12.0 Limara fapponica curlew 769 675 137 105.4 92.4 18 13.8 12.2 Nwrvnicrtarquata Whiibrel 409 460 441 180.4 202.7 135 55.2 62.1 Nwncnivr phaeopus Total Palaearaic waders 33 779 3 191.7 6032.9 3 CV3.5 401.1 670.6

“Resident” waders African Black Oyster- 685 629 83 56.9 52.2 95 65.1 50.2 catcher Haematopus moquini Whtefronted Plover 49 126 386 18.9 48.8 281 13.8 35.4 CharadrilLtma

Charadriur pallidus KiIUiQ’r Plover 39 110 111 4.3 12.2 127 5 ,o 14.0 Char&uspecuarius Threebanded Plover 32 98 1 0.0 0.0 7 0.2 0.7 Charadnus rricollalir Blacksmith Plover 171 270 25 4.3 6.8 35 6.0 9.5 VaneUurarmorur Ethiopian Snipe 128 226 0 2 0.2 0.5 Gdinago nigripennis Avoat 324 399 45 14.6 18.0 175 56.7 69.8 Recwvirostra avosetta BlackwingcdStilt 167 267 20 3.3 5.3 81 13.5 21,6 Himantopur himonroptu Total “resident” waders 726 104.3 149.1 880 163.3 209.8 Total waders 34 505 3 2%,0 6182,O 3965 564.4 880.4

Chertnutbande%i%r 36 10s 55 2.0 5-8 n 2.8 8.1

Non-waders White Pelican Pekcanus onocrotalus Grc Heron A r d a cinerea

L X % Y E e r o n Ardca mrlanocephala Littlc Egret E n~garzetra B Y ack Stork Ciconia nigrcr

*Sacred Ibis Tlrrakionrir aethiopicus

+Africans P,ataka P b i l 1

#Greater Flamingo Phoenieoptenu tuber Lesser Flamingo Phocnicoprenu minor E tianGoose A $ k e n a e g y tiaws

+South African &el- duck Tadoma cana

+Cape Shoveller Amsmithii YeUowbillcd Duck AMSUndULUa

+CapcTeal Amcapemis African Marsh Harrier Circus rMivonu

+Kelp Gull Lonu dominicanus

+Hadaub’s Gull Lonu hartlaubii Caspian Tern

* % E S ~ c t i c T e r n S t e m hirundolparadisea Antarctic Tern Sterna vittata

‘Sandwich Tern Sterna san&vicenu Swift Tern Sterna bergii

*LittleTem Stcmadbi ON p i 4 a n J L ccrvle nrdir

10 500 1440

870

1 390

500

3000

1586

1790

3400

1900

2 130

1322

661

992

441

518

900

296

570

138

138

251

200

100

83

3306

988

727

%l

519

1544

1048

1128

1666

1 169

1253

938

615

788

485

531

742

378

562

237

237

342

297

195

174

5

18

0

0

50

1

mi 18

313

0

12

4

0

101

24

1

637

506

8

868

0

51

5

1

1

52.5 16.5

25.9 17.8

25.0 268

3.0 1.5

318.8 210.6

32.2 20.3

I 064.2 521.3

25.6 l5,O

5.3 3.8

100.2 79.5

10.7 11.6

0.5 0.5

573.3 472.9

149.8 191,O

4.6 4.5

119.8 206.1

0

10

1

1

58

0

392

24

4280

Mo 16

0

12

28

40

2

750

652

5

24

51

0

2

0

4

14.4

0.9

1.4

29.0

621.7

43.0

14 552.0

570.0

34.1

7.9

27.8

17.9

1 .o 675,4

193.0

2.9

3.3

7.0

0.4

0.3

9.9

0.7

1 .o 30.1

410.8

27.1

7 130,s

350.8

7 -4

22.1

19.4

1.1

556.5

246.5

2.8

5.7

12.1

0.6

0.7

Totalnon-waders 2825 2 525.4 1818.2 6652 16803.4 8 855.9

Totdinvertebrate feeders 36208 5 450.3 7 613.5 10 115 16 675.3 9 278.6 GrandTolal 37 330 5 821.4 8000.2 10617 17376.8 9 736.3 - -

+I waders are invertebrate feeden: for non-waders, # = Invertebrate feeder, ’ = Palacarctic migrant, as classified by Siegfned (1981), with the exwp ~onofKelpGullwhichftcdsmostlyoninvertebratesat LangcbaanLagoon(P A.R. Hockeypcrs. mmm.)

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148 UNDERHILL: WATERBIRDS AT LANGEBMN OSTRICH 58

ter counts for each species. The sum of the medians for each species was used to estimate the typical population size and composition. Biomass (kg) was computed using mass data for each species obtained from Summers & Waltner (1979), Siegfried (1981), Maclean (1985) and Underhill (1986b). Daily energy expenditure (W/day) was computed using the formula DEE = 11,87.M0.608, where M is the mass of the species in grams (Wals- berg 1980).

RESULTS

Population size and composition, biomass and daily energy expenditure

All species with a median count greater than unity in either summer or winter are included in Table 1 which also lists scientific names. The waders in this table thus occurred in at least six of either the summer or winter counts and the non- waders in at least five. The total population size (sum of the medians for each species) was c. 37 500 in summer, and c. 10500 in winter (Table 1). Waders formed 92 % (37 %) of the total summer (winter) population, 93 % (78 %) of these being of Palaearctic origin (Table 1). Five species accounted for 92% of the summer wader population: Curlew Sandpiper (59,9 %), Grey Plover (10,5 %), Sanderling (8,3 %), Knot (8,1%) and Turnstone (5,7 %) (Table 2). There are approximately 1 750 ha of inter-tidal sandflats and 600 ha of saltmarshes (Summers 1977), so that the average density (birdsha) was 15,9 in summer of which 14,7 were waders, and 4,5 in winter, of which 1,7 were waders.

The total biomass in summer (5821 kg) was a third of that in winter (17368 kg), when Greater and Lesser Flamingos formed 87 % of the biomass (Table 1).

Species with the largest population DEE were Greater Flamingos (7,13 x 10" kJ/day) in winter, and Curlew Sandpipers (2,84 x 10" kJ/day) and Grey Plovers (1,13 x 106 kJ/day) in summer. The

TABLE 2 &MPosmON OF WADER POPULATION AT LANGEBMN LA- GOON IN SUMMER (s) AND WINTER (w), COMPUTED AS PER- CENTAGE MEDIAN NUMBERS, BIOMASS AND ESTIMAlED EN- ERGY REQUIREMENTS. SPECIES WITH A VALUE EXCEEDING

0,5 % IN ANY COLUMN INCLUDED IN TABLE.

Species s w s w s w Numbcrs Biomass Energy

B k k Oystercatcher h t o n e Rin@ Plover Whtefronted Plover Chestnutbanded Plover Kittlitr's Plover Grey Plover Blacksmith Plover Curlew Sandpiper Little Stint Knot Sanderling orcenshank BartailedGodwit curlew

0.2 2.4 1.7 11.5 0.8 5.7 5.7 18.6 7.0 15.3 6.9 18.1 0.7 0 0.4 0 0.5 0 1.1 7.1 0.6 2.4 0.8 4.0 0.2 1.9 0.1 0.5 0.1 0.9 0.3 3.2 0.1 0.9 0.2 1.6

10.5 13.1 23.8 20.0 18.3 18.6 0.1 0.9 0.1 1.1 0.1 1.1

59.9 28.5 35.1 11.2 45.9 17.8 0.9 0.1 0.2 0,O 0.4 0.0 8.1 4.7 122 4.7 11.0 5.2 8.3 5,3 4.8 2.0 6.2 3.2 1,3 2.8 2.7 3.9 2.1 3.7 0,6 0.8 1,8 1.6 1.2 1.4 0.4 0.5 3.2 2.4 1.5 1.4

Whimbrel 1.3 3;4 5;s 9;s 3;3 7.1 Avocet 0.1 4.4 0,4 10.0 0.3 8.0 BLsdrwin edStilt 0.1 2.0 0.1 3.4 0.1 2.5 m c r w An 0.2 0.3 0.0 0.0 0.3 0.0

total DEE in summer was 8,OO x l@ kJ/day (77,3 % waders and 6,5 % flamingos), and in winter was 9,73 X 106 kJ/day (9,0% waders and 73,3 % flamingos). Averaging over both the sandflats and the saltmarsh, the estimated DEE was 0,34 kJm-*day-' in summer and 0,41 kJm-2day-' in winter. However, flamingos forage partially in the sub-littoral zone (NOME 1982), Greater Fla- mingos feeding from the benthos (to an estimated depth of 0,5m), and Lesser Flamingos from the water column (Maclean 1985). About 500ha of Langebaan Lagoon has a depth at low tide of less than 0,5m. If, as a first approximation, it is as- sumed that Greater Flamingos obtain about one quarter of their food from the sub-littoral zone, and Lesser Flamingos are excluded, the DEE of the avifauna of the inter-tidal sandflats and saltmarsh remains 0,34 kJm-2day-1 in summer but should be revised downwards by 22% to 0,32 kJm-2day-' in winter.

Annual and seasonal fluctuations in population size, biomass and daily energy expenditure

The summer counts for the more abundant Pal- aearctic wader species for each year have been expressed as a proportion of the median, and plotted

l.*. 7. 77 7. 7. I 0 I 1 a2 a1 a4 a. a.

FIGURE 2

Fluctuations, relative to the median, in the summer populations of selected species of waders

(Charadrii) at Lmgebaan Lagoon, 1976-1986.

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CURLEW 8 A N O P l P C R ( 2 0 0 7 2 )

100

0 *MI

; Sir-- 0 / \

S A N O E R L I N O ( 2 0 4 7 1

W M I Y O R C L ( 4 4 1 )

60 O I

0

FIGURE 3

The winter populations of selected species of Palaearctic waders (Charadrii) expressed as a per-

centage of the median summer population.

on a logarithmic scale, so that increases or de- creases of the same magnitude are represented by equal deviations from the median (Fig. 2). For these species, winter counts in each year were expressed as a percentage of the median summer count (Fig. 3).

The Palaearctic wader population in winter was, on average, 11,5% of the summer population (Table 1). However this figure vaned between 2,5 % and 30,1%, and for Turnstones, Curlew Sandpipers, Grey Plovers, Bartailed Godwits and

possibly Knots, shows a fairly consistent three- year pattern, with large overwintering populations in 1977, 1980, 1983 and 1986 (Fig. 3). The population of non-waders increased by 250 % in winter. A few other species displayed marked seasonal changes. Palaearctic terns were largely absent in winter. The flamihgos, migrants from within the subcontinent (Berry 1975), increased on average tenfold in winter, but fluctuated greatly (Tables 1, 3). In addition, their length of stay at Langebaan Lagoon vaned considerably from year to year (Western Cape Wader Study Group unpubl. data) but from April to August large numbers of flamingos were usually present (Liversidge et al. 1958). Antarctic Terns wintered in small numbers along the Atlantic coast, rather than within the lagoon itself. Avocets and Blackwinged Stilts occurred in greater numbers during winter than in summer. One adult Avocet, ringed in April 1983 at Langebaan Lagoon, was recovered 288 km to the northeast (31 17 S; 2011 E) near Calvinia in November 1985 (SAFRING unpubl. data).

The annual variation in numbers, biomass and DEE of the avifauna was smaller in summer than in winter. Much of the variability in winter was attributable both to large fluctuations in the number of non-waders, particularly flamingos, and to three-year cycles in the abundance of certain Pal- aearctic waders (Tables3,4; Fig. 3).

Annual energy consumption The average annual energy expenditure for all

birds (except cormorants) at Langebaan Lagoon was estimated to be 3 141 x 106 kJ, or 133,6kJm-2 yr-'. Of this, the waders accounted for 1604 X 106 kJ or 68,2 kJm-Vr-', and all birds feeding on invertebrates 2 983 x 106 kJ or 126,9 kJm-2yr-'. Put- tick (1977,1978,1979,1980) has estimated that the mean annual production of invertebrate species in the uppermost 60mm at Langebaan Lagoon is 705 kJ m-2yr-1. Assuming an assimilation efficiency of 75% (Hockey 1984), the invertebrate feeders removed 3977 x 106 kJyr-' (169,3kJm-2 .yr-'), or 24% of the total production of invertebrates. Waders removed 2138 x 106 kJyr-' (91,O kJm-2yr-'), or 13 % of the total production.

D I s c u s s I o N

Population size, composition andfluctuations The species composition reported here (Table

2) conforms quite closely with the results of earlier surveys (Liversidge et d. 1958; Pringle & Cooper 1975; Summers 1977; Robertson 1981). Martin & Baird (1987) observed that prior to about 1950 there were more Curlews than Whimbrels in

TABLE 3 NUMBERS OF FLAMINGOS AT LANGEBMN LAGOON, MIDWINTER, 1973-1986. COUNTS FOR 1973 AND 1975, WESTERN CAPE

WADER STUDY GROUP (UNPUBL. DATA), REMAININGYWRS, UNDERHILL (1986)

Year 1973 1975 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986

Greater Flamingo 217 1071 38 1057 5308 8'724 4500 4 110 5631 4090 4451

Lesser Flamingo 97 124 0 0 183 1209 443 430 300 500 307 5000

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TABLE 4 NUMBERS, BIOMASS AND DAILY ENERGY EXPENDITURE OF PALAEARCIYC AND “RESIDENT” WADERS AND NON-WADERS AT

LANGEBMN LACOON, SUMMER AND WINTER, 1975-1986

Waders Non-waders All birds Numbers

Palae- resi- =tic dent Biomass DEE No. Biomass DEE No. Biomass DEE

Summer 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 Winter

8 36234 53s 3 3% 6431 36 769* 3 3%. 6 431. - _ _ - - _ _ - - _. __ 37 896 648 3 817 ioSi 8 38544’ 3 8ii* iGi* 38 933 628 3688 6971 1 949 762 769 41 510 4450 7740 35 103 983 3131 5966 3408 1603 1528 39494 4734 7494 34 447 673 2955 5 827 3 864 2841 1922 38984 5796 7749 38 849 1% 3 938 7 281 5 593 3 8S1 2994 45 178 7189 10281 _. - _ _ .. __.

30860 888 3104 5764 5256 6 % 4264 33004 9846 10028 27 441 570 2553 4904 3 647 4 360 2 715 31 658 6913 7 619 33 495 973 3304 6 163 5 809 2815 2397 40277 6 119 8560 32 595 892 3399 6232 13030 3963 4419 46517 7362 10651 37345 1187 3 798 7071 7695 3 745 3052 46040 7543 10 123

1975 1 2 2 3 1 108 353 538 2 331’ 353. 5381 - _ _ - _ _ _ --- --- - _._ _ _ _ 8 1976 3 822 509 523 833 4 331’ 523’ 833’

1977 3 437 71 1 657 983 2 829 4958 2795 6977 5 615 3 778 1978 852 1479 383 538 1471 1446 1060 3802 1 8 9 1598 1979 6 936 927 834 1497 3 276 5 671 2981 11 139 5 965 4478 1980 9840 746 1180 2073 7929 19184 10259 18515 20964 12332 1981 2 322 961 526 763 13017 33 817 17558 16300 34 343 18 321 1982 2 513 966 532 793 8 146 18059 9654 11 625 18591 10447 1983 9060 728 1113 1935 7688 16862 9 104 17467 17975 11 039 1984 2 983 1283 622 958 9 167 22 120 11 667 13 433 22742 12625 1985 2 768 1266 5 14 823 8533 17782 9779 12567 182% 10602 1986 10 397 840 1241 2206 10230 19961 11 308 21 467 21 202 13514 ’ non-waders not counted

southern Africa. Evidence of this at Langebaan Lagoon is that Gill (1934) in April 1934 recorded Curlews but not Whimbrels, whilst in March 1956, in the areas surveyed, there were about 100 Whim- brels but only a few Curlews (Rudebeck 1963). The population of Knots in southern Africa is be- lieved to have increased during the decade 1%5 to 1975 (P. A. Clancey in lift. to M. Waltner; Waltner 1985). Quantitative evidence for this increase is that in March 1956 there was one Knot per 340 Curlew Sandpipers (Rudebeck 1963), compared with an average ratio of 1 : 7,4 in summers between 1976 and 1986 (Table 1). There is no evidence to suggest that the increase has continued in the past decade (Fig. 2).

In March 1956, the total number of Palaearctic waders counted at Langebaan Lagoon was 20 OOO of which 17000 were Curlew Sandpipers (Rude- beck 1963). It is not possible from the descriptions of the areas investigated to determine precisely the coverage achieved, but probably more than 65 % of the intertidal area was surveyed, suggesting a maximum Palaearctic wader population of c. 3OooO (25 000 Curlew Sandpipers) in late summer 1956. These estimates are comparable with the summer populations between 1976 and 1986. In contrast, the estimates of the total Palaearctic wader population obtained by extrapolating from partial counts (41 OOO in March 1973,46 % of inter- tidal area surveyed, 55000 in March 1974, 55 % surveyed) (Pringle & Cooper 1975) are higher than the total counts of any comprehensive summer census between 1976 and 1986. During this period, between 50 % and 72 % of the Curlew Sandpiper summer population was observed in the area surveyed in March 1974, when 20784 Curlew Sand- pipers were counted. Thus it is likely that Pringle

& Cooper’s (1975) estimated total population of 38000 Curlew Sandpipers in March 1974 was not an overestimate, but a result of a population build- up between 1969 and 1973. Of these five breeding seasons, only in 1972 did breeding fail in the Tai- myr Peninsula (Underhill 1987), with 1%9 being an exceptionally successful breeding year (Sib- son 1970; Stanley & Minton 1972). In contrast, for the 11 breeding seasons between 1974 and 1984, Curlew Sandpiper breeding success was poor in eight years (Underhill 1987). This was possibly responsible for the steady decrease in Curlew Sandpiper numbers from 26 000 in summer 1976 to 17000 in summer 1985 (Fig. 2). The successful breeding season in the boreal summer of 1985 (Moser 1985; Parslow 1986; Underhill 1986c; Spearpoint 1986) corresponded to an increase in the Curlew Sandpiper population at Langebaan Lagoon to 21 W i n summer 1986.

Following breeding seasons with high productivity and adult survival, many first-year birds “overflow” from British and Dutch estuaries further south to, for example, western France, to estuaries which are not extensively used in years of low wader numbers (Baird et af. 1985; Pienkowski & Evans 1985). The implication is that the northern estuaries are approaching the limits of the numbers of waders they can support, and that population sizes in southern estuaries should fluctuate widely. Baird et al. (1985) identify Langebaan La- goon as an example of a wetland at the southern end of a migration route with a large year-to-year variation in numbers. However, between 1976 and 1986, the summer population of Palaearctic waders at Langebaan Lagoon has fluctuated within fairly narrow limits (22 % below the median to 11 % above) (Table 4; Fig. l ) , although there is

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evidence of larger populations in 1973 and 1974. This analysis of the abundance of waders provides no conclusive evidence that Langebaan Lagoon is an “overflow” locality for first-year waders dis- placed from further north.

Similarly, the generalization of Baird et af. (1985), based on observations in western Europe, that first-year waders migrate no further south than necessary, stopping at the first suitable locality, is simplistic. If this were the case, Lange- baan Lagoon, at the southern end of the East At- lantic Flyway, would receive an influx of first-year birds only in years of extremely high breeding productivity and adult survival. Langebaan Lagoon, in fact, receives an influx of first-year birds every year, including years of low breeding productivity (Summers etaf. 1987b; Underhill 1987).

A correlation between breeding productivity of Dark-bellied Brent Geese Brunru bernicfa bernicfu and Curlew Sandpipers was noted by Robertson (1981), who attributed the relationship to weather conditions in the Taimyr Peninsula, Siberia, where both species breed (Cramp & Simmons 1977, 1983). Longer series of data have revealed a synchronized three-year cycle in the fluctuations in breeding productivity of these species (Summers 1986; Underhill 1987), as well as for Turnstones (Summers et af . in prep.) and Sanderlings (Sum- mers et af. 1987). Because most overwintering Pal- aearctic waders at Langebaan Lagoon are first- year birds, it is likely that Grey Plovers, Knots and Bartailed Godwits display the same three-year cycle in breeding productivity (Fig. 3). All seven species breed on the tundras of the Taimyr Penin- sula (Cramp & Simmons 1983). Recoveries there of Curlew Sandpipers (Elliott et al. 1976) and a Sanderling (Summersetuf. 1987b) ringed at Lange- baan Lagoon, and recoveries of Turnstones and a Grey Plover on the Black and Caspian Seas, on the Great Circle route to the Taimyr Peninsula (Sum- mers et af. 1987a), provide evidence of the breeding origins of these species. Recoveries of Knot north of the equator are along the east Atlantic coastline, between Mauritania and Norway, and along the Baltic and White Seas, with none from the breeding areas (Waltner 1985). Using the tech- niques of Roselaar (1983) to separate subspecies, Waltner (1985) indicates that both the nominate race canuhcs which breeds in the Taimyr Peninsula and Severnaya Zemlya, northern Siberia, and the race islundica which breeds in northern Greenland and the Axel Herbert and Ellesmere Islands in northern Canada (Cramp & Simmons 1983) are present at Langebaan Lagoon.

Years of high breeding productivity of tundra waders, as measured by overwintering first-year birds at Langebaan Lagoon a year later, occurred when lemmings Dicrostonyx torquutus and Lem- m u sibiricus were abundant on the Taimyr Penin- sula; 1976, 1978, 1979, 1982 and 1985 (Dorogov 1983; Summers 1986; P. Tomkovich in firt. to R. W. Summers; Fig. 3). The probable causal fac- tor linking the three-year lemming cycles to breeding productivity is Arctic Foxes Afopex fagopus and other predators which prey on lemmings when they are abundant, but subsist on the eggs and

young of ground-nesting waders and waterfowl in years of lemming scarcity, severely reducing breeding success (Larson 1960; Roselaar 1979; P. Tomkovich in Pienkowski 1983; C. S. Roselaar in Cramp & Simmons 1983; Summers 1986; P. Tom- kovich in fin. to R. W. Summers). By contrast, the proportion of overwintering Greenshanks and Whimbrels which breed in the temperate zone (Cramp & Simmons 1983) shows relatively little fluctuation, indicating a more uniform breeding success each year.

The number of Turnstones at Langebaan La- goon in winter has exceeded 75 % of the median summer population in 1974 (Pringle & Cooper 1975), 1977,1980,1983 and 1986 (Fig. 3), and was larger than the previous summer’s population in 1974 and 1977. All these winters immediately fol- lowed boreal summers of high breeding productivity. The large populations during these winters are possibly enhanced by movement of first-year birds from the exposed and storm-prone open shores of the western Cape to the sheltered feeding areas in Langebaan Lagoon (Pringle & Cooper 1977; Sum- mers et al. in prep.). There are, however, no ringing recoveries to support this hypothesis, and further research on this point is required.

Energy expenditure and consumption The appropriateness of Walsberg’s (1980) for-

mula for bird populations at Langebaan Lagoon receives support, for Curlew Sandpiper at least, from Puttick’s (1980) estimate that the average daily energy intake of Curlew Sandpipers was 180 kJ/day (determined from direct observations of prey items and foraging). With an assimilation efficiency of 75 %, the assimilated energy intake would therefore be 135 kJ/day. The average DEE (based on observation of activity budgets) was 125 kJ/day (Puttick 1980). Walsberg’s (1980) formula estimates the DEE of Curlew Sandpiper to be 138 kJ/day (Table 1).

Puttick (1980) estimated that Curlew Sand- pipers alone consumed 86,7 kJm-2yr-1, but based her calculations on a summer population of c. 28 OOO increasing to 37 390 in March, and a winter population of 13 300 birds. These population figures were based largely on the partial surveys of Pringle & Cooper (1977), and, although probably close to reality for this period (see above), are considerably higher than median counts over the period 1975 to 1986. Revising Puttick’s (1980) calculations, using summer and winter population figures from Table 1, and the estimated monthly energy intakes estimated by Puttick (1980: Table 2), her estimate of annual energy intake by Curlew Sandpipers is reduced by more than 50% to 42,3 kJm-*yr-l. This figure is close to the estimate of 40,O kJm-2yr-’ obtained using Walsberg’s (1980) formula.

Baird et af. (1985) claimed that total energy consumption by all birds feeding at Langebaan La- goon was 142kJm-2yr-’, using the data of Summers (1977) and estimating total energy consumption at 5 x BMR. However, the data of Sum- mers (1977) relate only to waders and not all birds; the multiple of 5 x BMR is possibly an overesti-

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mate (Ebbinge er al. 1975). Baird et al. (1985) also appear to have excluded the area of saltmarsh from their calculations. Summers (1977) used 4 X BMR to estimate total energy consumption of waders to be 87,6 klm-vr-’, very close to the estimate of 903 kJm-Yr-’ obtained in this paper.

NOME (1982) and Engelmoer et al. (1984) con- sider that the waders at the Banc d’Arguin, Mauri- tania, consume nearly all the available prey before emigration, and exist on very narrow foraging margins. In contrast, waders at Langebaan La- goon removed 12 % of the total production, and all birds feeding on invertebrates removed only 24 %. The percentage of production removed by other predators of invertebrate (crabs and fish) is un- known, but it seems unlikely that Langebaan La- goon is at carrying capacity with respect to waders.

The impact of flamingos on energy consumption at Langebaan Lagoon has not previously been rec- ognised, and requires further research. Flamingos move to the coast during the dry winter season that prevails over much of the interior of southern Africa, and breed in years when conditions are suitable, mainly at Etosha Pan, Namibia, and Makgadikgadi Salt Pans, Botswana, but excep tionally at localities such as De Hoop Vlei, Cape, Van Wyksvlei, Cape, and Lake St. Lucia, Natal Uys ef al. 3963; Porter & Forrest 1974; Berry 1975; Broekhuysen 1975; Robertson & Johnson 1979). Brooke (1984) summarizes other attempts at breeding by flamingos in South Africa. Thus, since the eastern and southern African populations of flamingos are thought to be separate (Berry 1975; Brooke 1984), the flamingos at Langebaan Lagoon probably breed in Namibia or Botswana. There are however no ringing recoveries to support this idea.

Langebaan Lagoon is unusual in that it is an example of a wetland at which the DEE in midsummer and midwinter are approximately equal. In summer, 75 % of the DEE is attributable to Pal- aearctic waders, in winter 73 % to flamingos, intra- African migrants, and most of the remainder of the DEE is attributable to resident species. This con- trasts with the situation in the Banc d’Arguin, where the energy requirement of the flamingos is 35 % of that of the wader population, but where flamingos and waders are supported simul- taneously during the boreal winter (NOME 1982). However, flamingo numbers at Langebaan La- goon have been observed to increase from midsummer onwards (Western Cape Wader Study Group unpubl. data), perhaps due to drought in the summer rainfall areas. Thus the greatest prey consumption may occur during March and April, the pre-migration fattening period for waders (Summers & Waltner 1979). Dietary overlap po- tentially exists between waders and Greater Fla- min 0s (Cramp & Simmons 1977, 1983; NOME

mine if food resources are limiting at this time of year.

The national significance of Langebaan Lagoon for waders

The wader population of the South African

198 1 ), and further research is required to deter-

shoreline and coastal wetlands between the Orange River estuary and Kosi Bay is approxi- mately350000 (Underhill &Cooper 1984a, 1984b, 1984c; Summers et al. 1987a). Langebaan La- goon thus supports c. 10% of the wader population on the coast of South Africa.

The wader population at Lake St. Lucia (13 500 waders, Ryan et al. 1986) which is the second most important wetland for waders between the Orange River estuary and Kosi Bay (Underhill & Cooper 1984b) is only 40 % of that at Langebaan Lagoon. Other coastal wetlands at which more than 5 OOO waders have been recorded are the Orange River estuary (7000), Olifants River estuary (7500), Rocher Pan (5000) , Berg River estuary (9500), Rietvleihfilnerton Lagooeaarden Eilandvlei (10 500), Strandfontein Sewage Works (5 OOO), Kleinmond LagoodBotriviervlei (5 000), Swart- kops River estuary and adjoining saltpans (6 OOO) and Richards Bay (lOO00) (Ryan et al. 1986; Underhill & Cooper 1984b; Summers et af . 1987a). Langebaan Lagoon emerges clearly as the most important wetland for waders in South Africa.

The international significance of Langebaan La- goon for waders

The East Atlantic Flyway for waders (NOME 1982) embraces all waders that spend the nonbreeding season south of the Arctic Circle in Nor- way and Iceland, in the remainder of western Eu- rope, and in Britain, Ireland, the Mediterranean basin eastwards to Italy and Tunisia, and the At- lantic coast of Africa (Fig. 1). Most of these waders breed between 70 W (Ellesmere Island, Canada) and 110 E (Taimyr Peninsula, Siberia). The estimate of the wader population using the flyway is about 7,l x 106 (NOME 1982; Engelmoer et al. 1984) of which Langebaan Lagoon thus supports c. 0,5 %. In spite of the fact that Langebaan Lagoon supports only 0,5 % of the wader population along the East Atlantic Flyway, there are only about 20 known wetlands on the flyway that regularly support larger populations of waders than Langebaan Lagoon during the boreal winter (Table 5; Fig. 1).

The Ramsar Convention on Wetlands of Inter- national Importance especially as Waterfowl Habitat, to which South Africa is a signatory (Smart 1976), lays down criteria for the number of birds of each species that qualify a wetland as internationally important. Of the Palaearctic migrants, Langebaan Lagoon has internationally important populations of Turnstones (median summer count 1976; qualifying criterion 500), Grey Plovers (3615; 800), Curlew Sandpipers (20672; 20000) and Sanderlings (2 847; 150). The populations of Knots (2 808; 3 500), Greenshanks (443; 500) and Whimbrels (441; 500) exceed 80 % of the criteria for these species.

The influence of distance from the breeding grounds on overall annual survival is poorly under- stood (Myers et al. 1984). Langebaan Lagoon is the southernmost wetland of significance for waders on the East Atlantic Flyway. The only comparable wetlands south of the Kunene River are Walvis Bay Lagoon and Sandwich Harbour

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TABLE 5 WETLANDS ON THE EAST ATLANTIC FLYWAY WITH AVERAGE NUMBERS OF WADERS EXCEEDING u)OOo DURING THE BOREAL

WINTER. L ~ R S INDICATE LOCATlON OF WETLANDS ON FIG. 1

Wetland Average number of waders in boreal Reference

International Wadden Sea, Denmark, Germany, The Netherlands A 580 OOO Smit & Wolff 1981

Dclta, The Ncthcrlands B 100 OOO Leeuwis er al. 1984 The Wash, England C 132 OOO Anon. 1978 Humber estuary, En land D 41 OOO Anon. 1978 Lindisfame. Englanj E 34OOO Anon. 1978 Firth of Forth, Scotland F 52 OOO Anon. 1978 Solway Firth, England, Scotland G 105 OOO Anon. 1978 Morecambe Bay, England H 179 OOO Anon. 1978 Ribble estuary, England I 63 OOO Anon. 1978 Mersey estu , England J 38 OOO Anon. 1978 Dee estuaryyn land, Wales K 73 OOO Anon. 1978 avern estuary, ingland. Wales L 70 OOO Anon. 1978 Shannon, Ireland M 43 OOO Prater 1981 Baic du Mont St Michel, France N 138 OOO Prater 1981 Golfe du Morbihan, France P 46OOO Prater 1981 Ansc dc 1 ’Ai uillon, France 0 106 OOO Prater 1981 OlcronNcnfee, France R 49 OOO Prater 1981 Rio dc Vigo, Spain S >36 OOO Smit & Wolff 1981 Aveiro, Portu a1 T 3oOOO Prater 1976 Tejo estuary, 8ortuBal U 59 OOO Bijlsmaetal. 1985 Gulf of Gabcs, Tulusia V 241 500 VanDijketal. 1984 Merja Zerga, Morocco W 45 OOO Kersten & Smit 1984 Banc d’Arguin, Mauritania X 2 247 OOO NOME 1982, Engelmoeretal. 1984 Saloum Delta, Senegal Y >110 OOO Dupuy & Verschuren 1978 Archipel des Bijagos, Guinea-Bissau Z “several hundredsof thousands” Fournier & Dick 1981 Walvis Ba La oon, Walvis Bay Enclave a 30 OOO Whitelaw eral. 1978 Sandwich karkur , Namibia b 3oOOO Whitelaweral. 1978

winter

Langebaan Lagoon, South Africa C 35 500 thisstudy

(Fig. 4). Waders at Langebaan Lagoon thus rep- resent the extreme strategy for migration and moult on the East Atlantic Flyway. For example, Turnstones breed in a very narrow circumpolar la- titudinal range in the Arctic, but spread out in the nonbreeding season across most coastal regions south of the Arctic Circle (Cramp & Simmons 1983). T h e primary moult of adult Turnstones at the Wash, England, occurs between early August and late October in about 80 days (Branson et at. 1979), but between late September and early Jan- uary in about 100 days in southern Africa (Sum- mers etal. in prep.). Also, between November and February, Turnstones in Britain average c. log heavier than in southern Africa (Feare & Summers 1985; Summers et al. in prep.). The additional (Pienkowski et al. 1979). Elliot et al. (1976) compared strategies of Curlew Sandpipers wintering in different parts of Africa, but had limited data from outside the southwestern Cape. A similar study has been made of Sanderlings in California and Peru (Myers et al. 1984), but no other direct com- parisons between birds spending the non-breeding season both north and south of the equator have been published. Langebaan Lagoon’s situation near the southernmost extremity of the flyway thus gives it added importance and interest.

ACKNOWLEDGMENTS

D. Abemeth , G. Avery, A. L. Bosman, R. K. Brooke, M. A. zonnor, J. Cooper, J. Graham, P. A. R. Hockey, A. Hunt, P. D. Morant, H. Pfister, J. S. Prin le, H. G. Robertson, P. G. Ryan, M. Schramrn, R. 8. S ummers, G. D. Underhill, B. C. Vanderwalt,

M. Waltner, D. A. Whitelaw, A. J. Williams and others articipated in the surveys. The South African Bird

Lnging Unit (SAFRING) provided information on the ringing recoveries. The Southern African Ornithologi- cal Societ the Foundation for Research Development of the C.&I.R., the South African Museum, the Percy FitzPatrick Institute of African Omitholog of the Uni- versity of Cape Town and the National Paris Board are thankedforsup r, R. K. Brooke, P. A. R. Hockey, H. G. r obertson, h?W. Summers, M. Waltner and D. A. Whitelaw commented on earlier drafts. This

aper is a contribution of the Western Cape Wader E tudy Group.

rt. J. Coo

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REVIEW

CODY, M. L. (ed.). 1985. Habitat selection in birds London: Academic Press., xvi & 558 pp., 83 text figures, 1 black & white plate.

This book is the twenty-second in the Physio- logical Ecology series by this publisher and, as al- ways, a credit to them. The 18 chapters in the book by some 22 authors look at habitat selection in birds from every possible angle. The introductory chapter forms the first part of the book and is in- tended to whet one’s appetite for the subject; this is to some degree successful although some topics such as “Habitat structure” are touched on too lightly. The second part of the book deals with specific species or taxonomic groups such as the Pied Flycatcher Ficedula hypoleuca and Old World sylviine warblers. The habitat selection in raptorial birds was very interesting and thought- provoking, mainly because the chapter is largely based on new, unpublished data. The chapters in the third part of the book cover habitat selection from the point of view of certain habitat types. In this section I particularly enjoyed the chapters on habitat selection in grassland and open-country bird by Cody and schrubsteppe birds by Wiens. These two chapters are in sharp contrast, taking different views of habitat selection in habitats where easily identifiable patterns (by humans) in

the habitat are difficult to find. From the other chapters in this section it is also quite clear that the scale of analysis is important when considering habitat types in habitat selection studies. The studies in temperate and tropical forest are interesting reading and make one fully realize that the hun- dreds of bird species which occupy the Amazon forest are a major challenge to studies on habitat selection in this habitat.

In Part IV, entitled “A variety of approaches to habitat selection in birds”, the subject is dealt with from the physiological, morphological, behavioural and migratory viewpoint and to me the first seven chapters were by far the most interesting in the book. The habitat-consumer interactions in frugivorous birds treated by Herrera is an excel- lent paper which shows that birds as seed-dispers- ers can probably improve their habitat to a large extent. The last chapter in the book considers sOme theoretical aspects of habitat selection and Rosenzweig develops a few useful but very diffi- culty models to follow.

Overall, a very useful book for anyone interested in habitat selection. The vast number of references alone makes the book worthwhile.

Roy A. Earlk

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Documents

WADERS (CHARADRII) AND OTHER WATERBIRDS AT LANGEBAAN LAGOON, SOUTH AFRICA, 1975–1986