NEW STRATEGIES OR OPPORTUNISM AMONG BIRDS : V

examples in the Sqhelian Region of West Africa

by Bernard W C A ORSTOM B.P. 1386 DAKAR S~NEGAL

I. INTRODUCTION.

Birds need a certain amount of food each day to satisfy their energy needs. To get this minimum amount of food, they have developped fishing, hunting and seed-gathering strategies. In the Sahel, major climatic variations greatly affect the amount of food qvailable, such as seeds, insects, etc. In recent times, humans have significantly altered the environnement. Birds have often had to adapt their feeding and reproductive behaviors to suit these ecological conditions.

Adaptation manifests itself either by oppartunistic behavior, i.e. birds promptly taking advantage of the abundant local resources, though this may not be in keeping with their usual behavior patterns. Similarly, they can also adopt new strategies related to feeding and reproductive behaviors or mpulting schedules.

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*" 22nd Intemational Ethological Conference

KYOTO (JAPON) 22-29 août 1991 I"

Compte-rendu

Plus de 500 participants d'horizons très divers ont discuté pendant une semaine de l'éthologie au sens large chez des groupes d'animaux aussi variés que les oiseaux, les primates, les insectes sociaux, les rongeurs, les poissons, les crustacés, etc. Les communications furent de très bon niveau.

Le matin, des séances plénières eurent pour themes : - Stratégies de reproduction ; - Ethologie appliquée ; - Economie du Sexe ; - Tactiques sociales des Primates ; - Evolution de la Sociabilité t - Prise die décision.

L'après-midi, les participants se partageaient selon leurs préférences entre les six salles où les sujets des conferenciers étaient encore plus variés. Voici quelques exemples des thèmes abordés :

- Stratégies de la reprodyction chez les oiseaux ; - Compétition interspécifiques chez les oiseaux ; - Comportement alimentaire ; - Problèmes liés a l'ecologie ; - Comportement humain : Analyse des Fonctions ; - Etho-pharmacologie ; - Ethologie appliquée ; - Groupes et Structures sociales chez les Mammifères ; - Stratégies de la reproduction chez les Arthropades

- Utilisation de l'Habitat chez les Poissons ; - Communication chimique ; - Interface Homme - Animaux ; - Comportement des Ptimates ; - communication acoustique ; - Développement du comportement ; - Prises de décision et Théories de Chasse ; - Apprentissage ; - Comportement génétique ...

marins

Un nombre important des sujets traités tendaient à déterminer les préférences des animaux selon les choix dont ils disposent : choix d'un partenaire pour la reproduction,

* 1 choix de la nourriture, choix de l'habitat . .. Ainsi les Tactiques ou les Stratégies développées par les espèces, consciemment ou non, furent abondamment discutées.

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Des expositions de nombreux posters sur les différents thèmes et discussions avec les auteurs, aux heures de repas, des projections de films vidéo/ le soir et des démonstrations de matériel de laboratoire ou de terrain complétaient cet emploi du temps déjà très chargé.

J'ai personnellement été fort impressionné par l'impeccable organisation japonaise. Les nombreux contacts que les participants ont pu prendre entre eux seront une suite très interessante de ce congrès. Je remercie 1'ORSTOM de m'avoir permis dfy asslster, et particulièrement la CS4 et le Departement MAA qui ont participé financièrement aux frais de ce voyage.

zz:z¿im j'ai pr6sinti.e intitulée "New Strategies birds : some xamples in siaheliari xegion of' West Africa" entrait dans le cadre des prdblhmes relatifs à 1'Ecologie. J'y montrais entre autres, l'adaptation du calendrier de mue ,et de reproduction du Canard

9 armé (Plectropterus gadensis) aux conditions d'environhement (comparaison entre delta du Sénégal et Delta central du Niger au Mali), ou les changements de zone d'hivernage des Barges a

a, queue noire (Limosa l ihosa) suite aux modifications du milieu.

Les communications orales seront publiées' dans les proceedings, mais en attendant, je peux mettre à la disposition de mes collègues qui m'en ont fait ou qui m'en feront la demande une copi'e des résumés des communications.

En marge de ce congrès, une excursion organisée le dimanche a permis à un gra'nd nombre des parqicipants de visiter l'aquarium d'OSAKA, le plus grand du monde, inaugure

' en août 1990. Le grand bassin central comprenant plus dè 5 O00 poissons est entouré d'aquariums plus petits, mais bien grands quand même, représentant différents milieux de la ceinture de feu du Pacifique. Les milieux sont très bien reconstitués, comme la forêt Bquatorienne, la grande barrière de corail, l'antarctique, les grands fonds du large du Japon ...

La prochaine conférence Internationale d'Ethologie se P tiendra à-Barcelone (ESPAGNE) en 1993.

The Sahel is just South of the great Sahara desert. Rainfall is very light (150 to 400 mm of rain per year). Birds can find, however., large flood zones where an. expense of rising rivers have sources further South. The three large flood zones are the Delta of the Senegal River (the border between Senegal and Mauritania), the Inner Delta of the Niger River (in Mali), ar;?a the Lake Chad Basin (the borders of Chad, Cameroon and Nigeiia).

Plants and animals have adapted to a short rainy (June ' to September) , a substancial vegetation and production, and a demographic ,explosion of all ki insects or other animals when conditions are favorable.

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season seeds

nds of

Map of Africa showing the Sahelian Region

III. EXAMPLES OF OPPORTUNISM.

A) ReDroductive onbortunism.

A study of the reproduction system of the Spur-winged goose (Plectropterus gambemis) in Senegal (TRECA, 1979 and TRECA, 1980) has shown that Spur-winged geese adjust their schedules for laying eggs and the number of eggs they lay to climatic conditions, i.e. the amount of rainfall and particularly the amount of grass growth. The differences can be significant according to the year. In 1978, hatching occured between November 2 and November 28, compared with October 17 to Nopember 1 in 1979.

Moreover, it is conceivable that years in which conditions were less favorable (1972 for exavple, when lack of rain prevented grass for growing more than a few centimeters high), Spur-winged geese did not reproduce at all. Thus, a gradual decline in the population can be seen. The loss of population growth can be overcome in a short period of time (TRECA, 1978) by significantly higher rates of reproduction during favorable years (up to 27 eggs per nest).

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€3) Feedins omortunism.

1) Black-tailed aoddit (Limosa limosa) The Black-tailed godwit is a bird whose long beak is

suitable for capturing animal prey in muddy soil. Moreover, in Europe, where it breeds, the godwit's diet consists almost exclusively of prey (BANNERMAN, 1931). It was quite surpr'ising to learn that godwits could cause a great deal of damage in African rice fields, where they make their winter quarters (CROOK, 1956 i TRECA, 1977).

* In fact, dietary studies (TRECA, 1984) show that

cultivated rice (Oryza sativa) and wild rice (Oryza breviligulata and O. barthii) make a substancial part of the

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Black-tailed godwit diet in the Delta of the Senegal River (See Fig. 1). A supplementary diet consists of seeds (primarily Graminae, Cyperacae, Nymph’eacae) and tubercles (Cyperacae). It was, thereforeteven more surprising that no trace of animal item has ever been found in the stomachs of some 207 godwits used in the dietary studies.

100% 90%

8 0 %

70%

60% 50%

40%

30%

20% 10%

0% J A S 0 . N D J F M A M J

tubercles

other seeds

00.breviligulata

Is Oryza sativa

Fig 1. Diet of the Black-tailed godwit in Senegal (N=207)

In captivity, we have been able to keep Black-tailed godwit by feeding them paddy rice (unhulled rice) and millet. The godwits took some grains of rice, then drank a little water to swallow the rice. In the wild, however, we have often observed Black-tailed godwits feeding on threshing areas where the ground is dry and very hard. Not having water nearby, did not seem to bother the birds.

The inadequate shape of the godwits' beaks for the kind of food they eqt is greatly compensated by the abundance of food they find locally, clearly an advantage. One should also note that like other species of migratory birds, the godwits from Europe are concentrated in bnly some spots along the Sahelián region after they make it across the Sahara desert, so food must be abundant for such a number of birds. Studies on the quantity of food available (ALTENBURG and van der KAMPF, 1985) show that there is less prey in the area frequented by the godwits in Sahelian Africa compared to that of their European feeding grounds. On the contrary, the seeds weigh 70 times

' more than preys in the Sahelian region.

2) Ruff (Philomachus pugnax). Tpe Ruff is considered very opportunistic. That is, it

will take advantage of every local food souce available (CRAMP and SIMMONS, 1983) J The Ruff has a wide range of food since his diet can be composed of nearly 100 per cent prey items (CRAMP and SIMMONS, 1?83), cultivated or wild rice (TRECA, 1990), and even peanuts as HÖTKER et al (1990) have recently indicated. The Ruff's feeding opportunism, as a result, becomes in fact a feeding strategy.

IV. E2CAMPLES OF ADAPTATION STRATEGIES TO LOCAL CONDITIONS.

A) Spur-winged geese (moulting in Senegal and Mali). Let us return to the Spur-winged goose (Plectropterus

gambensis) to study its moulting habits. In Senegal, most Spur-winged geese shed their flight feathers (primary and

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9 secondary) in August/September. They cannot fly at this time since moulting for most of the wing fegthers occurs almost simultaneously. They later regain their ability to fly by the beginning of the mating season which take place in September/ October/November. When the rice matures in November/December, Spur-winged geese are able to feed in the rice fields and sometimes greatly damage the rice.

On the other hand, in Mali, a neighboring country to Senegal (on the same latitude), the moult of the flight feathers for most of the Spur-winged geese occurs later, around December/January, so after the mating season (TRECA, 1983 ; TRECA, 1989). At the time rice is maturing, Spur-winged geese are, for the most part, unable to fly. For their safety, they keep their distance from the rice fields occupied by humans.

The reason for this change of schedule is simple. When the Spur-winged geese shed their flight feathers, they must be protected from their predators (including humans). The safest period occurs when the floqd reaches its highest level. This occurs around August/September in Senegal. In Mali, however, this event takes place only between October and december due to the delay caused to the advancing flood by the Inner Delta of the Niger River, a vast deltaïc basin some 50,000 km2. The moulting dates are, therefore, a strategy the Spur-winged

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geese adopt to deal with their environnement and to guarcintee their safety.

€3) Black-tailed godwits (changing winteP quarters) We have already established that the Black-tailed godwit

has a rice-based diet during a certain part of the year. Godwits have now become very dependent upon rice fields, according to ALTENBURG and van der KAMPF (1985). Yet,after a comprehensive census taken on the Atlantic coast from the

e south of Mauritania to Guiena Bissau, the above authors

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observed that of 125 to 140 thousand godwits counted, only

eight per cent of the birds were not in the rice fields. The figures derived for the Delta of the River Senegal show that in spite of an increase of the rice-cultivated surfaces, the number of Black-tailed godwits is decreasing. According to BEINTEMA and DROST (1986)/ the Delta of the Senegal River has lost its role of a major site for Black-tailed godwits. The latter seem to prefer the rice fields in the South of Senegal and Guinea Bissau. This is du$ to the continued improvement of rice farming in the delta of the Senegal River. The result is that godwits no longer find enough space to move around and feed among the rike plants.

V. CONCLUSION.

These few examples shQw that birds are equkped with certain adaptation skills in order to deal with varying local factors. This adaptation could mean using opportunistic behaviors to take advantage of certain surroundings conditions i.e. food availability. On the other hand, this adaptation

. could also mean adopting new strategies i.e. changing winter quarters in the case of the Black-tailed godwit and in that of the Spur-winged geese, changing their moulting schedules to guarantee maximum protection,

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As migration occurs among certain populations of the Spur- winged goose, for example, between the Delta of tfie Senegal River and the Inner Delta of the Niger River (in Mali), it would be of great interest to know whether or not the birds who fly from one delta to the other change their moulting schedules, or if they maintain the ones they were accustomed to previously.

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VI. BIBLIOGRAPHY :

ALTENBURG (W) et van der KAMPF (J) , 1985, Importance des zones humides de la Mauritanie du Sud, du Sénégal, dB la Gambie et de la Guinée-Bissau pour la Barge a queue noire (Limosa 1.limosa) UICN/WWF - projet 3096, CIPO-project 9238 Fondation néerlandaise pour la Protection des Oiseaux rapport RIN 1985-1, 117 pp.

BANNERMAN (D'A.), 1931, The Birds of Tropical West Africa with special reference to those of Gambia, Sierra Leone, the GOld Coast and Nigeria, Oliver and Boyd, Edinbugh and London, vol II, 428 pp.

BEINTEMA (A.J.) et DROST (N), 1986, Migration of the Black- tailed Godwit. G e r ' f a u t , 76 : 37 - 62

Africa, vol I, Academic Press, London, New York, 521 pp.

CRAMP S . et SIMMONS (K.E.L. ) , 1983, Handbook of the Birds of Europe, the Middle East and North Africa, The birds of the Western Palearctic, VOL. II, Waders to Gulls, London, Coutry Life LTD, 232 pp.

CROOK (J.H.), 1956, Gird damage and crop protection in West Africa, polygr.

FALL P. et TRECA B., 1990, Le Parc National des Oiseaux du Djoudj, effets de la sécheresse et de la construction du barrage de DIAMA sur l'inondationet la vdg&tation, mémoire de fin d'étude, école nationale des cadres

BROWN (L.H.), URBAN (E.K.) et NEWMANN (K.), 1982, The Birds of

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ruraux, 76 pp. HÖTKER H., BRUN H.A. et DIETRICH S . , 1990, ObservatiÒns de

chevaliers combattants (Philomachus pugnax) s'alimentant de cacahuètes. L ' O i s e a u et R.F.O. 60 (4) : 312 - 314.

du riz au Sénégal. Bull. IFAN 39, Ser. A (3) : 682 - 692

TRECA B., 1977, Le probl&me des oiseaux d'eau pour la culture

TRECA B., 1978, Evolution des populations d'anatidés éthiopiens et estimations des dégâts d'anatidés sur

Cah. ORSTOM, ser. Biol., vol XIXI n04 : 339 - 345

(Plectropterus gambensis), au Sénégal, Malimbus 1 (1) : 29 - 31 canard armé (Plectropterus gambensis) au Sénégal Malimbus 2 (1) : 25 - 28

in West Africa ? Discussion. Anntial Rice Review Meetinq, may 1983, W&DA/83/ARR- 31, 15 pp. ronéotypées.

TRECA B., 1984, La barge à queue noire (Limosa limosa) dans le delta du Sénégal : régime alimentaire, données biométriques, importance économique. L'Oiseau et R.F.O., 54 (3) : 247 - 262

TRECA B., 1989, Les risques de dégâts d'oiseaux sur les i rizières sahéliennes. c - in : Le risque en Agriculture, ELDIN M. et MILLEVILLE

t m le riz dans le delta du Sénégal,

TRECA B., 1979, Note sur la reproduction du canard armé

TRECA By, 1980, Nouvelles données sur la reproduction du

TRECA B., 1985, Do water birds really destroy irrigated crops

P. (Ed.), Ed. de 180RSTOM, coll. A travers champs, Paris : 167 - 175.

TRECd B., 1990, Regimes et préférences alimentaires d'Anatidés et de Scolopacidés dans le delta du Sénégal, étude de leurs capacités d'adaptation aux modifications du milieu, exploitation des milieux cultivés. Thhse de doctorat, Museum National d'Histoire Naturelle, Paris, 200 pp.