Ill·
m.
tre ies ,he
or
or
~se
ion ied 79~
ved )rt·
vise bo
IOll,
1lri·
the lost ied,
the :cies :rial y is that s of
;uch
>wer eco- , the sses.
rried '.om-
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~ for
I and
·ds to Re.v.,
lcean.
Is for Black-
metal . Am.
3-206, dwar<l 29-32, lineral ,abirds 11/11r1·t.
a11dard Waler.
VaJl Aarde, R .. I. Voeding, /111bito1s11<1wke11r on vnortpla111i11g van die Wildehuis.kw (Fe/is cat11s Li111111e11.r, l 758) op Marionei/a11d.
MSc thesis, University of Pretoria. 1977.
Yan Zinderen JBakker, E.M . .Jr. Comparative avian ecology. In Marion and P,ri111'e haward lsl<11.cls, edited by E.M. van ZinJeren Bakker Sr., J.M. Winterbottom, & R.A. Oyer. 161-172. Cape Town, A.A. Buikema, 1971.
Vogel, A.I. A Tt•x1b11ok of' Qun11t1/(//i11e f11orga11il· A11a/ysis. London, Longmans, 1939.
Watling, H.R.. & Watling, R.J. Preliminary prern1ra1ion uf mollusc5 for trace metal analysis. FIS Special Rep .. 76. CSI R, Pretoria,
1975.
Williams, A.J. & Burger, A.E. Notes on non-breeJing seabirJ3 a,
lhe Prince Edward islands. Cor111ora11t, S, 11-14, 1978.
Williams, A.J., Siegfried, W.R., Burger, A.E. & Herruti, A. The Prince Edward islands: a sanctuary for seabirds in the southern oceans. Bia/. Comen•., 15, 59-71, 1979.
Williams. A .. 1., & Berru!i. A. Minernl and energy contributions of feathers of penguins, gulls and corn1-lrants to the M~1rion Island turrestrinl cco~y~te111. S. Afr. J. 411t11rr/. Rew., 8, 70·7:\, I 978.
Will/ams, A.J.. Burger, A.E. & Rerruti, t\. Mineral and energy contributions of carcasst!s of' selected species of seabirds 10 the Marion !slant! tcrrcstrinl ecu~ysl.:--n. S. Af,· . .I. A11/1,1r,·1. Rc,s., R, 52-58, 1978.
Williams, A.J ., Burger, A.E .. Bcrruli, A. & Siegfried, W.R. Ornitho- logical research on Marion Island, 1974-75. S. Afr. J. A111wd.
Re~., S, 48-50, 1975.
Mineral and energy contributions of carcasses of selected species of seabirds to the Marion Island terrestrial ecosystem
A.J. Williams, A.E. Burger and A. Berruti Percy FitzPatrick Institute of African Ornithology, University of Cape Town, Rondebosch 7700.
S11b-A11tarctic Marion Island 111111,wlly rccei\1es a11 estimated 125,9 t (dry weight) oj carcasses he/onging lo I] species <~/' seabil'ds. Tlu.1se carcasses m·e initin!/y tle1Josi1,:;d iv1thi11 m, area of 128 k111". 11/111ost all of whif'/1 is coastal lowlanrl. M11r- 1a/ity o/at/11/1 birds whilst hreeding is negligible. Adu/I pe11g11i11:i which die during their a111111al 111011/t-fast cv111rib11te so111e 46,9 I (dry weight) vf avian material to the ecosysle111. More tha11 165 000 chicks of the J 'l species die each year he/ore j/Nlgi11g. Th<'Y ('1)11trib111e 7tJ,7 t (dry weight) o.f material to the uosyste111. pn1g1,i11 chicks forming 99 Jiff cent of this. An area of 4 km• weceives 77 per cent of 1he pe11.r111i11 chick ('([rcaxs 111a1erial. Over 1/,e remaining 124 km" area in which chicks die. the average mmua/ i11p111 of chick carcass mtlferial is 1.5 /(g ha '. T.lie co11ce11tmtio11.1· of selected mineral elements (Ca, Cc/, C11, K, Nlg, Mn, N, Na, I', Sr, Z11) in the bodies o/' pcmg1,i11 c/zick.r were detern1irll'il, mu/ the Iota/ 111ass of' mineral e/1i111e11ts thus c1111trib11ted lo the e,·o.1·ysle111 calrnlated. The e1w1•gy contributed hy penguin chick cw·1·ass1•s alone <111101111/s
111 l,57>' 10" k.J per a,11111111.
Introduction
In many terre:strial ecosystems birds are important links in lrophic webs (Weiner & Glowacinski, 1975). Seabirds feed primarily or solely at sea. Any avian products - eggs, guano, feathers and carcasses - which seabirds deposit on land whilst breeding or moulting ashore, represent a net transfer
<lf material to the terrestrial ecosystem. Preliminary studies
of the role of seabirds as mineral element and energy trans- porters are being made on sub-Antarctic Marion Island
(46 54'S, 37"45'E) in the southern Indian Ocean (Siegfried,
1978).
This naper reports the mass of carcasses of adults and chicks of 12 s.pecles of surface-nesting seabirds which breed on Marion lsland, and t11e amounts oi energy ant'. ,d1:.1:.tt.~
mineral elements contai11e<l in the carcasses
or
chicks ol' four species of penguins. The spectcs concerne<l are: king nenguin.Ap1e11ot!y1es pa1r,go11ic11s: gentoo penguin, Pygoscelis papua:
macaroni penguin, Eudypte.v chryso/opl/11.1'; rockhoppor pen- guin. E. d1ry.1·om11w; wandering albatross, Dfolllt'dea ex11/a11s:
sooty albatross, Phoehefria /i1.1·ta: light-mantlec.l sooty albatross, P. palpehr(Jta; norLhern giant petrel, Macro11ectas ha/Ii: southern giant petrel, /VI. ;:igu11rc•11s: imperial cormorant. Phalt1cmcorax alhivt'nfer; sub-Antarctic skua, C'aflwracta a11tarctif'a: and kelp gull, Lams dumi11ic111111.1·.
Materials and methods
Studies of the breeding biology of sub-populalions of each species on Marion Jsla,,d provided Jata 011 gwwth in chick mass, chick mortality, and phenology l Berrnti, l 979;
Williams, Burger & Berruti, unpublished d:.ita). Most of the species a:re synchronised breeders and for these. seasonal calculations were based on the date by which 50 per cent of the chicks had hatched. Ge11100 and king nenguins are asynchronous breeders and allowance has been made for this in the calculations. Chick mortality in the king penguin could not be studied closely on Marion Island, nor are data on this topic available in the literature. We have assumed (from Williams & Burger, unpublished data) that 10 per cent
or
king penguin chicks die between hatching and the end of May at a mean massor
0,5 kg: a further JO per cenr die during the period June.September at a mean mass of J kg; amJ that a fw ther 5 per cent die between October and January at a mean mass uf 5 kg. Mortality of .idult penguins during inou It was estimated from field observations. The mass of adult penguins which starve to death during moultwas assumed 10 be the 5ame as the minimal individual mass for the species as reported in Lhe literature.
Tiu (w.:.ili.t.ate. the plottinl! of the distribution of avian
S. Afr. T, Antarkt. Nav., Deel 8. 1978
2 5 6 7 8 9 10 II 12 13 14 15 16 17 18 19 20 21 22 23 24 25
A B C D E F G H
J I<
L M N 0 p
Q
R
t
O 1 2 3
45 .
K ilometres
Fig. l. Breeding distribution of seabirds (species listed in Table I) on Marion Island. Light-mantled sooty albatrosses nest in the quadrats indicated by a+, albatrosses, giant P.!trels, sub-Antarctic skuas and kelp gulls in the quadrats marked by an X, and penguins, albatrosses, giant petrels, imperial cormorants, sub-Antarctic skuas and kelp gulls in the solid(}, shaded area.
The limit of the coastal plateau ( 150 m above sea level) is marked by a broken line.
Table 1
Annual production of hatchlings and the number and mass (kg wet weight) of chick carcasses of 12 species of seabirds on Marion Island.
King penguin Gentoo penguin Macaroni penguin N
B Rockhopper penguin Ai
B
Total all penguins Wandering albatross Sooty albatross
Light-mantled sooty albatross Northern giant petrel Southern giant petrel Imperial cormorant Sub-Antarctic skua Kelp gull
Total excluding penguins Grand total
'Siegfried el al. (1978).
No. chicks hatched' No. chicks which die Mass of chick corpses
138 400 55 570 140 890
2 390 I 660 750
1340 295 280
328 400 72 250 67 950
15 950 10 360 8 410
46 650 2J JJO 34 980
533 130 163 465 253 260
l 290 275 406
1 320 712 I 204
112 59 I JO
161 23 5
995 123 SI
432 178 128
669 231 82
272 200 62
5 251 1 802 2 048
538 881 165 267 255 308
2Eudyples penguins lay dimorphic eggs giving rise to chicks of dtlferent hatching weight.
978 $. Afr. J. Antarct. Fies., Vol. 8., 1978
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material. Marion Island was divided into a series of J km•
quadrats (flg. I). Siegfried et al. ( 1978) give details of lhe distribution of surface-nesting seabirds on the island. Chicks die close to their natal sites. and the majority or penguins moult al or near their natal colonies. ll was Lherefot·e assumed that carcasses of chicks and moulting penguins were distri- buted i.n the same way
as
breeding birds.Carcasses of penguin chicks used for chemical analyses were of birds known to have clied of starvation within 24 hours of collection in the field (older king penguins). or were birds specially killed for Lhis study, Marion island is a naLure reserve and only a Limited number of specimens could be collected. The chicks analysed included three king penguins, two gentoo penguins, two macaroni penguins and three rock- hopper penguins. The chicks were of known age. All carcasses were frozen within four hours of collecrioo and were stored in a deep freeze until processed.
Carcasses were weighed when taken from the deep freeze . They were cut into small pieces using a knife or axe, and then minced until .finely homogenised. In larger specimens the skin, feathers and subcutaneous fat were processed as a separate unit from the main body. The minceu material was oven-dried at 60 "C until a constant weight was attained.
Random aliquots of the dried mince were analysed to determine energy content and mineral element concentra- tions. Energy values were determined using a Gallenkarnp ballistic bomb calorimeter. The con~ntration of selected mineral elements was determined by means of a Varian Techtron AA-6 atomic absorption spectrophotometer using acetylene fuel and flame spectroscopy (Pringle et al. I 968), after the organic material had been treated as described by Walling and Watli.ng (1975). The following clement concentra- tions were determined: copper, cadmium, potassium, mag- nesium, manganese, sodium. strontium, and zinc. Total calcium was determined by EOTA titration using Erichrome Black T indicator (Vogel, 1939). Phosphorus concentraLions were determined by stannous chloride procedure (Taras el al.
l 971) and nitrogen by sl.andard Kjeldahl procedure (GroJ- zinski et al. 1975). In order Lo obtain a mean value three determinations were made on each sample .
Results
Number and mass of chick carcasses
The number of chicks hatched annually on Marion Island by the 12 species considered here is 538 380, of which an estimated 165 300 die before fledging (Table J ). The total fresh mass or these chick carcasses is 255 308 kg, of which penguin chick carcasses form 99 per cent
Chick carcasses occurred in l28 I km" quadrats, almost all on the coastal lowland. The 4 km' area which contained the five largest penguin colonies received 77 per cent of all penguin chick carcasses, the annual input from chick car- casses in this area bdng 152, I kg (dry weight) ha-•. Over the remaining J 24 I km2 quadrats the average input
or
chickcarcasses was 1,5 kg (dry weight) ha-1 yr--1•
Chick mortality was spread throughout ll1e year, though 44,6 per cent of the chick carcass mass was recorded in December-February and 43,7 per cent in June-September (Table 2). King penguin chicks died principally during the winter months, when they received scarcely any food; about 30 per cent of the chicks starved to death or. in a weakened state, were killed by predators (Williams & Burger, unpub- lished data).
56 $. Afr. T. Antarkt. Nav., Deel 8. 1978
Table 3
Number and mass (kg wet weight) of penguins which die on Marion lsland during the annual moult.
King penguin Gentoo penguin Macaroni penguin Rockhopper penguin
'Williams er al. (in press).
•Williams, unpublished data.
Minimum No. breeding birds No. non-breeding birds Total no.
mass adult
bird moulting' dying moulting~
9" 430470 2 150 274 500
44 2 690 13 2 760
3s 899 800 4500 891 900
J ,36 186 600 933 342 400
'Calculated using Mougia's co-efficients (Prevost, 1976).
'Williams et al. (1977).
Table 4
birds dying dying
2 750 490()
28 41
8 920 13 420 3 420 4 350
3Stonebouse (1960).
Total minimal mass of fresh corpses
44070 164 40 260 5 660 90154
Monthly production (kg wet weight) of carcasse!; of penguins which die on Marion Jsland during the annual moult.
Oct. Nov. Dec. Jan. Feb. Mar, Apr. May Jun.-Sep. Total
- - - -
King penguin'
breeding J l 370 3 790 3 790 18 950
non-breeding 7 540 17 590 25 120
Gentoo penguin•
breeding 15 21 15 SL
non-breeding 45 34 34 I IJ
Macaroni penguins
breeding 5 310 7 970 13 290
non-breeding 8 090 18 880 Z.6970
Rockhopper peng_uinz
breeding 606 606 l 2l0
non-breeding I 780 2 670 4450
Total l I 320 11 330 21 380 8 150 20 715 l.! 030 8 576 606 0 90154
% 12,6 12,6 23,7 9,0 23.0 8,9 9,5 0,7 () 100
'Barrat (1976). "Observations on Marion Jsland.
Table 5
Total weight and energy content of the annual crop of penguin chick carcasses on Marion Island
Dry weight Mean energy Total energy
(kg) content content
(kJ/g) (kJ) X 10~
King penguin
Pre-winter carcass 1 520 22,1 33,7
integument I 040 29,91 31,I
Mid-winier carcass 25 160 17,2 432.7
integumenl. 16 830 20,4 343,3
Post-winter carcass 4 900 22,l 108,5
integument 3 280 16,6 54,5
Gentoo penguin
Age 1-10 days wbole 37 20;2 0,8
Age 11-30 days whole 295 1S,:J 5,4
Macaroni penguin
Age l-25 days whole 9 730 21,8 212,0
Age 25-70 days carcass 5 820 20,2 ll7,5
integument 1 940 20,t 39,0
Rockhopper penguin
Age 1-10 days whole 280 18,J 5,t
Age l 1-30 days whole 760 19,5 14,9
Age 31-70 days whole 7 420 23,l l 71,4
Total 79 000 1570
'Chicks at this stage accumulate stores of sub-dennaJ lipid before the winter fast.
S. Afr. J. Antarot. Res .. Vol. 8., 1978
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57
Numbers and mass of adult ,carcasses
Few aduJt birds belongin,g to the 12 selected species die on Marion Island during the breeding season. Small numbers of pengufos are killed by giant petrels and some birds die from accidents. The only significant mortaJity of adult birds observed on Marion Island concerned penguins during their annual moult. Penguins cannot remain at sea during their moult, and are therefore unable to feed during the moulting period. Moult takes some 24-37 days in these species of penguins (Richdale, 1957: Warham, 1971; Stonehouse, J960).
Birds with insufficient food reserves may actually starve to death or be so weakened that they fall prey to giant petrels.
We have no detailed mortality data for lhis period of the penguins' cycle but estimate that O,S per cent of the population of adults which have bred in the same year, and J per cent of the immature birds, may die during moult. AduJI penguins which die during moult may therefore contribute 90 154 kg (fresh. weight) to tbe ecosystem of Marion Island each year (Table 3). At a minimal water content of 48 per cent in the carcasses of starved penguins (Williams et al. 1977) the total dry weight of these carcass,es would be 46 881 kg.
Moulting penguins are distributed over 74 km2 of the island (Fig. I) and 82,4 pe1r cent of the carcasses occurred in the 4 km2 area occupied by the five largest penguin colonies.
This area annually receives. an input of 96,6 kg ha-1 of adull penguin carcasses. Tile remaining 70 km' has an average input or 1,2.kg ha-• yr-• Differnnt species and age classes of pen- guins moult at different times, so that per\gui.n mou]L on Marion Island is spread over eight months, October-May.
Some 55,7 per cent of the fresh mass of adult penguin car- casses enters the ecosystem during December-February (Table 4).
Energy and mineral elemen1t contents of carcasses
The totaJ amount of energy contained annually in penguin chick carcasses is about 1.57 ~ I 09 kJ (Table 5). The concentra- tions of selected mineral dements (Table 6) and th.e known dry mass of penguin chjck carcasses (Table 5) enable calcula- tion of the total mass of 1the selected elements contained in the annual crop of chick ,carcasses (Table 7). Penguin chick carcasses potentially contribute 9,7 t of nitrogen and 2,4 t of calcium, as well as suli:>stantial amounts of some of the other selected elements, to the Marion Island ecosystem.
Carcasses of adult penguins which died during moult were not analysed as part of tlnis study. Nitrogen determinations were used by Williams et al. (1977) to calculate protein content in moulting mac:aroni and rockhopper penguins . These determinations indlicate that nitrogen forms about 5 per cent of the total fl·esh mass of penguins during the latter stages of moult. Applying this level of nitrogen content to the fresh mass or adult penguin carcasses, we estimate the nitrogen content of these carcasses to be 4 500 kg.
Discussion
There have been relatively few studies of the impact of birds on ecosystems, largely because of the methodological di.ffi- cullies involved. All previous studies h,\ve been made in the northern hemisphere and most have concerned energy flow (e.g. Kale, 1965; Odum et al. 1962). Few studies have assessed mineral contributions of birds (Weir. 1969; Sturges et al. 1974). As far as is kinown, the present study is the first attempt to assess the contribution or bird corpses to a terrestrial ecosystem in the southern hemisphere.
Our calculations are subject to a number of shortcomings.
58 S. Afr. T. Antar'kt. Nav., Deel 8. 1978
Table 7
Mass of selected macro-elements (kg) and micro-elements (g) corntaioed io the annual crop of penguin chick carcasses on Marion Island.
King Gen too
Element penguin penguin
Mncro-e/eme11ts
Nitrogen 6 102 37,90
Phosphorus 515 7,()4
Sodium 469 J,20
Potassium 307 3,67
Magnesium 79 0,26
Calcium I 867 9,SO
Micro-eleme11rs
Copper 713 0,99
Cadmium 25 0,04
Manganese 248
1,n
Zinc 6 733 32,94
Strontium 3 598 1,24
These are largely related to differences in phenology, and chick mortality and growth amongst the various specic:s chosen for study. lt is particularly difficult to calculate the total mass of chicks at death. Not only does mass chang,e rapidly with growth but also at any age the mass of a chick may vary greatly according to whether the chick was healthy and killed by a predator, or has starved to death. Our figure for the percentage of adult penguins which die during moullt is only a very rough estimate. Nevertheless, we feel that our calculations are of the correct order of magnitude and thus give a meaningful indication of the mass of material annually deposited on Marion fsland. in the form of carcasses c,f selected species. Our calculations of energy and mineral element contents of carcasses relate only to penguin cl1ick.s and our samples, two or three specimens per species, are minimal.
In comparison with other avian materials, such as eg~;, guano, and teathers, carcasses form large units and thei.r visual impact is enhanced by their slow rate of decomposition in the cool sub-Antarctfc conditions. This led the authors to anticipate that carcasses would be relatively more important in terms of mass than other avian contributions to the ecosystem. ln fact, the total dry weight of carcasses (125.9 It)
is a much smaller amount than the annual input of guano (Burger el al. J 978) and of feathers (Williams & Berruti, 1978) from the same species.
The bulk (67,2 per cent) of both chick and adult carcass~:s is deposited in a 4 km" area occupied by the five largest penguin colonies. whereas the remainder of the penguin carcasses are deposited within I 00 m of the sea. If the impact of carcasses on the Marion Island ecosystem was limited to this small area, the effoct of carcass material on the ecosystem would be reduced. Almost all carcass material is, however, consumed by predatory a11d scavenging species, primarily giant petrels, skuas, gulls and the losser sheatl1blll, Chionis mi11ol', buL also to a lesser extent by feral cats, fr/ifs cat1,s, and possibly mice, Mus 111usc11/11s. These animuJls frequently occur over inland areas of the island and there redistribute, as guano, eggs, feathers, faeces, urine and ca1·- casses, material derived from penguin carcasses. The overall importance of avian carcasses to the Marion lsland ecosystem will only be fully appreciated whe11 studies OJl other aspects of the island's ecosystem are conducted or completed.
Macaroni penguin
2460 160 114 111 24 272
152 I I 670 84 J 154
Rock.hopper penguin
l 156,0 95,J 92,6 55,6 21,4 291,5
86,4
0,7 45,0 1 156,0 1,2
Acknowledgements
Total
9 758,2 778,7 679,4 478,4 125,6 2 440,8
952,9 27,6 1964,4 8 007,6 4 754,6
Sdentific research at the Prince Edward islands is carried out under the allspices of the South African Committee for Antarctic Research. Fi11anciaJ and logistical support is provided by the Department of Transport. We thank K.C.
Davies, S.K. Frost. G.M. Crouse, L.D. Cwati, L.F.
Mansfield, H.G. Robertson, and Dr G.A. Eagle for their help.
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