WHY DO GREAT WHITE PELICAN CHICKS DIE SUDDENLY ON AREL ISLAND, BANC D' ARGUIN, IN MAURITANIA? A. J. CRIVELLI*

WHY DO GREAT WHITE PELICAN CHICKS DIE SUDDENLY ON AREL ISLAND, BANC D' ARGUIN, IN MAURITANIA? A. J. CRIVELLI* There re five mjor costl upwelling regions in the world : the Cliforni current off the USA, the Humboldt current off Peru, the Cnry current off Northwest Afric, the Benguel current off Southwest Afric nd the Somli current in the lndin Ocen est of Afric, in which bout hlf of the world's fish c:tches re mde. The cold, nutrient-rich wters of these regions fvour high primry production, leding to optiml reproduction nd survivl of fish nd providing n exceptionlly high fish production for mrine ecosystem (Scheffer, 1970 ; Cushing, 1971 ; Brber & Smith, 1981 ; Hrtline, 1980 ; Glntz, 1980). The most spectculr consequence of this high fish production is the presence of thousnds or even millions of sebirds which tke d v n tge of this bountiful food su pp! y (Crwford & Shelton, 1978 ; Duffy, 1983 ; Duffy et l., 1984 ; Schreiber & Schreiber, 1984 ; Duffy & Siegfried, 1987 ; Adms et l., 1992). Most of the costl upwellings re sesonl. Only the upwelling on the Peruvin cost is permnent but even this vries in intensity with the seson. Along the Muritnin cost (West Afric) there is lso sesonl costl upwelling (Wooster et l., 1976 ; Sevrin-Reyssc, 1993) which ffects the wters of the Bnc d' Arguin ( 19.45 N 16.16 W) from December to April. From the mon th of My, wrming of the wter column occurs, then in July wrm wter coming from Guine rrives nd remins until November. As in other res of upwelling, the Bnc d' Arguin lso supports lrge concentrtions of fish-eting sebirds (de Nurois, 1969 ; Mhé, 1985 ; Cmpredon, 1987) nd prticulrly Gret White Pelicns. The hevy nd spectculr mortlity of chicks in December-Jnury of the Gret White Pelicn (Pelecnus onocrotlus) nd of Cormornts (Phlcrocorx crbo lucidus) nesting together on Are! islnd bd been recorded s erly s the 1960s (de Nurois, 1969) nd ws gin noted in the 1970s by Trotignon & Trotignon ( 1981) nd Trotignon et l. ( 1980) in the 1970s nd finlly by Mhé (1985) nd Cmpredon (1987) in the 1980s. Up to 1080 ded chicks were counted in Jnury 1980 (Trotignon & Trotignon, 1981). These uthôrs lso noted hevy kleptoprsitism by pelicns on cormornts nesting on Are! islnd. Ali the uthors immedite! y concluded tht the dult Gret White Pelicns were no longer cpble of feeding their chicks nd tht these died from strvtion. But no-one could find rtionl explntion for this fct. We therefore propose to review the sttus of the * Sttion biologique de l Tour du Vlt, Le Smbuc, F- 13200 Arles. Rev. Ecot. (Terre Vie), vol. 49, 1994. - 321

Gret White Pelicn in Afric, nd prticulrly in West Afric, to study the phenology of pelicns nesting on Are! islnd nd ttempt to explin why lrge proportion of the Gret White Pelicn chicks htched on Are! islnd die suddenly from the beginning of the month of December. METHODS Two expeditions were mde to the Bnc d' Arguin, one in November 1980 nd the second in September 1981. The priority im on both visits ws to collect regurgittes from chicks, to ssess the breeding phenology of the species nesting on Are] islnd nd to crry out continuous observtions of pelicn ctivity on the islnd. The secondry im ws to determine the preferred feeding sites of pelicns on the Bnc d' Arguin nd the periods during which they fi shed. Trvelling over the Bnc ws done t high tide in Zodic, nvigting by compss. Observtions on feeding sites were lso crried out t night. RESULTS THE STATUS OF PELECANUS ONOCROTALUS IN AFRICA There re two distinct popultions of Gret White Pelicns (Pelecnus onocrotlus) : n Africn popultion nd Plerctic one. The size of the ltter hs been estimted t little over 10 000 pirs (Crivelli et l., 1991), nd the Africn popultion contins bout 75 000-80 000 breeding pirs (Crivelli & Schreiber, 1984). In our present stte of knowledge there is no indiction of ny exchnges between these two popultions. Three geogrphicl «sub-popultions» cn be considered to exist in Afric : western popultion (Muritni, Senegl nd Mli), centrl popultion (Chd nd Cmeroon) nd southem-estem popultion (Djibouti, Ethiopi, Keny, Tnzni, Zmbi, Botswn, Nmibi nd South Afric). The southem-estem sub-popultion is thriving. The centrl sub-popultion hs gretly declined, notbly with the disppernce of breeding Gret White Pelicns in Nigeri nd only few hundred breeding pirs remining in Cmeroon (Mhé, 1988) nd in Chd. The western sub-popultion hs chnged gretly over the lst twenty-five yers. With the exception of the regulr nesting on the Bnc d' Arguin nd t Aftout es Sheli in Muritni, no breeding by Gret White Pelicns hd been recorded in West Afric until 1972 when Jrry nd Lriguderie (1974) described the first ttempt t nesting by Gret White Pelicns t Djoudj in Senegl. Unfortuntely this ws unsuccessful nd it ws not until 1976 tht the first successful breeding by Gret White Pelicns ws observed t Djoudj (Dupuy, 1976). Since this dte Gret White Pelicns hve bred irregulrly t this site. In Mrch 1991, colony of bout 2 000 pirs ws observed (C. Perennou, pers. comm.). A second colony settled on snd bnk t Kllisye for few yers, but this colon y no longer exists. ln sorne yers up to 10 000 breeding pirs hve been counted in Senegl. Finlly, the Gret White Pelicn bred only once in Mli t Toguéré Koumbé, following exceptionlly hevy rins (Urbn, 1984). - 322 -

The first mention of the Gret White Pelicn on the Bnc d' Arguin dtes from Portuguese silors in the 15th century. They do not however stte whether the species ws nesting t this period. lt ws in 1957 (de Nurois, 1969) tht the breeding of Gret White Pelicns ws recorded for the first ti me in West Afric on Are! islnd on the Bnc d' Arguin. Since this dte breeding by Gret White Pelicns hs occurred regulrly on Are! islnd. Between 1957 nd 1969, 100 to 400 pirs were recorded (de Nurois, 1969) ; there ws th en n increse between 1977-1982 with 800 to 1 500 pirs (Trotignon & Trotignon, 1981 ; Mhé, 1985 ; this study ). Cmpredon (1987) confirmed tht this increse continued in 1984-85 with c. 3 000 pirs. The Gret White Pelicn hs only bred on Are! islnd t the Bnc d' Arguin. Of li the islnds of the Bnc d' Arguin this is the furthest from the cost. lt is never submerged even t equinoctil spring tides, nd is therefore vilble for breeding birds throughout the yer. In ddition, birds re completely protected from terrestril predtors such s jckls nd hyens. PHENOLOGY The Gret White Pelicn is totlly bsent from the Bnc d' Arguin from Februry to the end of June. The first individuls rrive t the Bnc in July nd the erliest lying hs been observed on the 17 August 1965 (de Nurois, 1969). The mjority of birds ly in September-November, but smll groups of nests with eggs cn still be observed between December nd Jnury. These lte clutches re probbly renesting ttempts. Becuse of the wide spred in breeding dte nd successive wves of lying, the breeding birds form very distinct cohorts. Within ech cohort li nests re synchronised, i.e. t the sme stge of development (± 5 to 10 dys). Between 17 nd 22 November 1980 7 breeding cohorts were counted, including 360 nests with men clutch size of 1.25 eggs/nest (Tble 1), crèche of 150 chicks ged 4-5 weeks nd nother crèche of 300 chicks ged 8 to 10 weeks, sorne of which were ble to fly. There ws significnt liner reltionship TABLE 1 Clutch size in breeding units counted between 17 nd 22 November 1980 on Aret islnd N of nests Stge Clutch size 41 eggs 1.24 Il eggs 1.00 106 eggs 1.35 60 htching 1.30 88 eggs 1.49 7 eggs 1.14 47 htching 1.21 Totl 360 Men ± S.D. 1.25 ± 0.16 Rnge (1-3 eggs/nest) - 323 -

between men clutch size per cohort nd the number of nests in the cohort (N = 7; r = 0.87, F = 13.96, P < 0.01). The lrger the size of the cohort the greter the clutch size (Fig. 1 ). The totl number of breeding birds ws estimted t between 800 nd 1000 pirs. At the sme dte 700 nests of Phlcrocorx crbo lucidus were counted, il t the egg stge. 0 o O o o 0 o o 0 o oo o 0 0 0 0 0 0 0 0 o oo o. o.o o o o o o o o o o 0 0 0 0 0 0 0 o o o o o o o o o o 0 0 0 0 0 0 Unit 3. 106 NESTS 0 o 0 o 0 0 o o. o 0 Unit 1. 41 NESTS Unit 2. 11NESTS Figure 1. - Clutch size in nests of 3 breeding units in 1980. Filled circles : nests with two eggs, open circles : nests with one egg. From 11-26 September 1981 three breeding cohorts of Gret White Pelicns were counted, totlling 350 nests, li t the egg stge. For technicl resons it ws not possible to determine the clutch size. At this time no cormornts were nesting on Arel islnd. A literture serch ws mde for li counts of ded Gret White Pelicn chicks on Arel islnd, to which were dded our own counts nd these hve been plotted ginst dte (Fig. 2). It cn be seen tht mortlity is negligible in October nd November, lthough mny chicks re present t this time, but mortlity becomes importnt from mid-december. Adults strt to leve the Bnc d' Arguin in mid-november nd by December-Jnury the mjority of dults hve left the Bnc nd heded south. The min «summering» sites (December-June) for Gret White Pelicns breeding in Muritni is presumed to be in Senegl nd Mli. FEEDING ECOLOGY The diet of Pelecnus onocrotlus breeding on Arel islnd is mde up of fish nd crustcens (Tb. Il), but prwns nd crb clws only mde up smli proportion of the food ingested. Most of the prey re of smli size (less thn 150 mm). - 324 -

.100 BOO e i9bo "' 800 u J: u loo O < w 0 20 e19b5 MONTHS.---WARM WATER ---41+---COL 0 WATER ----+ Figure 2. - Chick mortlity throughout the breeding seson on Arel islnd. TABLE Il The diet of the Gret White Pelicn Fish & Crustce Number of prey Rnge of prey fork species (% occurence)* length (mm) Syngnthide Syngnthus sp. 6 (16.6) 158-172 Serrnide Mycteroperc rubr 5 (16.6) 94-137 Dicentrrchus punctt 8 (33.3) 89-290 Pomdsyde Pomdsys rogeri 5 (16.6) 90-95 Spride Dentex sp. 2 (11.1) 172-255 Pomcentride Abudefduf nlogus 132 (94.4) 40-139 Gobiide Gobius pgnellus 26 (83.3) 20-112 Blenniide Mlcoctenus sp. 4 (16.6) 66-80 Mugilide Mugit cephlus 1 (5.5) 420 Atherinide Atherin sp. 8 (5.5) 38-71 Soleide Sole sp. 1 (5.5) 125 Peneide Peneus duorrum 52 (88.8) 60-65 * Number of regurgittes 18, collected in November 1980. 325

On sever) occsions Gret White Pelicns hve been observed ctively feeding t night in the shllowest wter in chnnels t low ti de or on the rising tide. On the 22 November t sunrise, Arel islnd ws completely deserted by dult pelicns, with the exception of few individuls tht still bd young chicks (less thn 15 dys). Ali rrivis nd deprtures bf dults were recorded until the end of observtions t 1400 h. The first birds strted rriving on the islnd from the feeding grounds from 0930 h, with pek of rrivis t 1100 h ; fter 1145 h no more rrivis were recorded (Fig. 3). No birds left the islnd before 1400 h ; the mjority preened themselves, slept or lofed fter feeding their young. The Gret White Pelicns breeding on Arel islnd cn go in serch of food s fr wy s Cp Timiris ((i5 km from Arel). The preferred feeding sites re round Arel islnd, in the Ajoueir-Ti dr region, the Sint-Jen by nd the re between Aoutif by nd Cp Tessit (Mhé, 1985 ; this study). N 250 200 r- 150 100 50 Low ti de y 0 6 7 8 9.--.--.-- r- - r- 10 11 LOCAL TIME.-- - High tide À 12 13 14 Figure 3. - Number of Gret White Pelicns returning to Are! islnd from their feeding grounds in ech 15 min period, in reltion to the stte of the tide. DISCUSSION The recent increse in the number of breeding pirs t Arel is certinly relted to the recent strt of breeding by Gret White Pelicns in Senegl. If this regulr breeding in Senegl continues, further increse in the number of breeding pirs on Arel islnd cn be expected. The men clutch size recorded on Arel islnd is prticulrly low (this study ; Cmpredon, 1987) compred to the vlue of 1.93 for Gret White Pelicns breeding in Greece (Crivelli et l., 1991b) nd 1.62 to 1.91 recorded in Est Afric (Brown et l., 1982). This low clutch size is ttributed to hevy predtion by Grey-heded Gulls (Lrus cirrhocephlus) nd Lesser Blck-bcked Gulls (Lrus fuscus). It is not surprising, therefore, tht the men clutch size in the lrger - 326 -

breeding cohort is greter thn tht in the smller cohorts, s it is likely tht there is less opportunity for gulls to tke n egg in lrge breeding cohort thn in smll cohort. Gret White Pelicn chick mortlity only relly occurs s from the month of December nd only becomes mssive in Jnury-Februry. It is indisputbly relted to the rrivi of cold wter (upwelling) on the Bnc d' Arguin t the strt of or mid-december. Although this mortlity occurs every yer it vries quntittively from yer to yer. When the mjority of breeding pirs strt breeding nd ly t the beginning of September, the number of chicks dying in December Jnury is lower thn when lrge number of birds strt breeding in October, since it tkes bout 100 dys from lying to fledging of the chicks. Preliminry nd limited results of our study of the diet of Gret White Pelicns in November, before the rrivi of upwelling, show clerly : ) tht the most bundnt species in the regurgittes in both numbers nd percentge occurrence is Abudedduf nlogus, fish typicl of wrm wter nd known to be bundnt in Senegl (J. Migret, pers. comm.) ; b) tht the mjority of the other species found in the regurgittes re species such s gobies, snd smelts, blennies nd pipefish, typicl of shllow wter. This lst point is supported by observtions of dult Gret White Pelicns feeding exclusively t low tide or on the rising tide in the shllowest prts of the chnnels, even if this mens feeding t night. The min dvntge for pelicns in feeding t low tide is tht the fish re concentrted in the chnnels nd the density is therefore much higher thn t high tide, mking the communl fishing of these birds more efficient. To our knowledge, this is the first time tht night-time feeding by Gret White Pelicns hs been recorded on regulr bsis (McNeil et l., 1993). In other res of Afric nd in the Plerctic night-time feeding ctivity hs only been observed ccidentlly, either on freshwters or costl hbitts. It should lso be dded tht it is unusul to observe Gret White Pelicns feeding in mrine environments. Unfortuntely, dt on the fish popultions of the Bnc d' Arguin re re still frgmentry, nd especilly so for the shllow wters (Cmpredon & Schrieken, 1989 ; J g er, 1993 ). Migret (1977) considered tht the rich re sources of the Bnc d' Arguin re essentilly mde of pelgie fish which come to this re to spwn. CONCLUSION The rrivi of the first Gret White Pelicns on the Bnc d' Arguin coïncides with the rrivi of wrm wter coming from the Gulf of Guine. Mssive mortlity of chicks still unble to fly nd the deprture of young cpble of flight nd of dults coïncides with the rrivi of cold wter (upwelling) which forces the wrm wter further south. This rther fst chnge of wter lso corresponds with drstic chnge in fish popultions, especilly in shllow wters, the preferred feeding site of Gret White Pelicns (Guillet & Crowe, 1981 ; Crivelli et l., 1991 b ; Crivelli, unpublished dt). In the cold wter period the fish popultion is composed minly of fish tht inhbit the deeper wters (Migret, 1977). The shllow wters re lmost devoid of fish nd only the cormornt is cpble of feeding here becuse of its bility to dive deeply. As the Gret White Pelicn only feeds t the surfce nd in shllow wter it is unble to cpture food, which cuses fmine mong the - 327 -

chicks still unble to fly nd forces dults nd fledglings to deprt towrds the south. At the height of the upwelling (Februry-Mrch) there re prcticlly no breeding fish-eting birds left on the Bnc d' Arguin ; only few Cspin Tems seem to breed t this seson (Mhé, 1985). Spwning by the fish of Bnc d' Arguin is observed t the onset of spring (Migret, 1977). From My onwrds, fish fry ppers in millions in the se-grss beds in shllow wter. It is exctly t this time of yer th t the l 0 or Il species of fish-eting birds (tems, gu Ils, Africn cormornts nd herons) strt breeding t the Bnc. The pek of the breeding seson for most species is in June (Mhé, 1985). Ail the fish-eting species feed only on fish of smll size nd cn only cpture fish in very shllow wter or t the se surfce ; they tke dvntge of the presence of these millions of fish fry to breed successfully. When the wrm Guine wter rrives the fry leves the se-grss beds nd withdrws to the north of the Bnc with the cold wter, nd retires to deeper wter. Agin, this phenomenon coïncides with the end of the breeding seson for the ten fish-eting species. Throughout the yer t the Bnc d' Arguin, there is therefore remrkble reltionship between the breeding phenology of the vrious species of fish-eting birds nd the presence of different fish popultions with vrying densities nd sptio-temporl behviour ptterns on which the feeding behviour nd fishing bilities of the fish-eting birds depend. SUMMARY The sttus of the Gret White Pelicn in Afric in the l980s is reviewed. During this period the size of the colon y of Pelecnus onocrotlus locted on the Muritnin cost t the bnc d' Arguin incresed ten-fold owing to n influx of birds coming from newly instlled colonies in Senegl. Gret White pelicns re bsent from the Bnc d' Arguin from Februry to June. The first birds instll on the Bnc in July, coinciding with the rrivi of wrm wters from the Gulf of Guine. The pelicns ly their eggs in successive wves from mid-august to the end of November. The clutch size is unusully low for the species (men 1.25 eggs/nest). There is positive reltion between clutch size nd the size of the breeding cohort (r = 0.87, P < 0.01). Hevy mortlity of chicks of il ges is recorded from mid-december onwrds, together with mssive deprture of dults towrds the south. This mortlity ppers to be due to the upwelling of cold wter which displces the wrm wter towrds the south : this hypothesis ws tested from supporting evidence. Observtions on the composition of chick regurgittes, the behviour of dults on the forging grounds (both during the dy nd t night, but exclusively t low tide) nd the timing of breeding of other fish-eting bird species confirmed this hypothesis. RÉSUMÉ Le sttut du Pélicn blnc en Afrique dns les nnées qutre-vingts est pssé en revue. Pendnt cette période l tille de l colonie de Pelecnus onocrotlus située sur l côte muritnienne u Bnc d' Arguin été multipliée pr dix grâce à un fflux d'individus provennt des nouvelles colonies sénéglises. Les - 328 -

Pélicns blncs sont bsents de février à juin sur le bnc d' Arguin. Les premiers s'instllent sur le bnc en juillet u moment où rrivent à ce niveu les eux chudes provennt du golfe de Guinée. Les pélicns pondent leurs oeufs pr vgues, de l mi-oût à l fin novembre. L tille de leur ponte est inhbituellement bsse pour l'espèce (1,25 oeufs/nid). Une reltion positive existe entre l tille de l ponte et l tille de l'unité de nidifiction (r = 0,87, P < 0,01). A prtir de l mi-décembre on observe une forte mortlité des poussins de tous âges et un déprt mssif des dultes vers le sud. Cette mortlité serit due à l remontée des eux froides (upwelling) repoussnt les eux chudes plus u sud : cette hypothèse est testée et étyée. Des observtions sur le contenu des régurgitts des poussins, le comportement des dultes sur les lieux de ggnge (de jour comme de nuit et exclusivement à mrée bsse) et l phénologie de reproduction des utres espèces d'oiseux piscivores confirment cette hypothèse. ACKNOWLEDGEMENTS This contribution is dedicted to the lte Professor Frnçois Bourlière. The expeditions to Muritni in 1980 nd 1981 were finnced joint! y by the Bnc d' Arguin Ntionl Prk nd the French Ministry of Coopertion. 1 would like to thnk Mr A. Touré, the former director of the Bnc d' Arguin Ntionl Prk, for his willing collbortion, Dr J. Migret for identifying sever! of the fish found in pelicn regurgittes nd Mr Erik Mhé nd his wife for their wrm welcome nd help t li times. REFERENCES ADAMS, N.J., SEDDON, P.J. & VAN HEEZIK, Y.M. (1992). - Monitoring of sebirds in the Benguel up_welling system : cn sebirds be used s indictors nd predictors of chnge in the mrine e ironment? In : Benguel tro P_ hic functioning A.I.L. Pyne, K.H. Brink, K.H. Mnn & R. HI1born (Eds). S. Afr. J. mr. Set., 12 : 959-974. BARBER, R.T. & SMITH, R.L. (1981). - Costl upwelling ecosystems. In : Anlysis of mrine ecosystems, A.R. Longhurst (ed.), pp. 31-68. Acdemie Press, Englnd. BROWN, L.H., NEWMAN, K. & URBAN, E.K. (1982). - Birds of Afric. Vol. 1. London, Acdemie Press. CAMPREDON, P. & SCHRIECKEN, B. (1989). - Fishes nd shrimps of the ti d] flts. ln : Report of the Dutch-Muritnin project Bnc d'arguin /985-1986, B.J. Ens, T. Piersm, W.J. Wolff & L. Zwrts (eds). RIN Rpport 89/6, Texel, 222-227. CAMPREDON, P. (1987). - L reproduction des oiseux d'eu sur le prc ntionl du Bnc d' Arguin (Muritnie) en 1984-1985. Alud, 55 : 187-210. CRAWFORD, R.J. & SHELTON, P.A. (1978). - Pelgie fish nd sebird interreltionships off the costs of South West nd South Afric. Biol. Conservtion, 14 : 85-109. CRIVELLI, A.J. & SCHREIBER, R.W. (1984). - Sttus of Pelecnide. Biol. Conservtion, 30 : 147-156. CRIVELLI, A.J., LESHEM, T. & JERRENTRUP, H. (l991). - Where do Plerctic Gret White pelicns (Pelecnus onocrotlus) presently overwinter? Rev. Ecot. (Terre Vie), 46 : 68-94. CRIVELLI, A.J., CATSADORAKIS, G., JERRENTRUP, H., HATZILACOS, 0. & MICHEV, T. (l991b). - Conservtion nd mngement of pelicns nesting in the Plerctic. ln : Conservtion of Migrtory birds, T. Slthé (ed.), ICBP Technicl Publiction, no 12 : 133-148. CUSHING, D.H. (1971). - Upwelling nd the production of fish. Adv. mr. Biol., 9: 255-334. DUFFY, D.C. & SIEGFRIED, W.R. (1987). - Historicl vritions in food consumption by breeding sebirds of the Humboldt nd Benguel upwelling regions. In : Sebirds, feeding ecolo gy nd rote in mrine ecosystems, J.P. Croxll (ed.), Cmbridge University Press, Englnd. DUFFY, D.C., HAYS, C. & PLENGE, M. (1984). - The conservtion sttus of Peruvin sebirds. ICBP Technicl Publiction, no 2 : 245-260. DUFFY, D.C. (1983). - Environmentl uncertinty nd commercil fishing : effects on Peruvin Guno birds. Biol. Conservtion, 26 : 227-238. 329

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