Biodiversity and Conservation9: 527–539, 2000.© 2000Kluwer Academic Publishers. Printed in the Netherlands.

Trends in the use of a small coastal lagoon bywaterbirds: Muni Lagoon (Ghana)

YAA NTIAMOA-BAIDU 1,2,∗, SAMUEL K. NYAME2 and ALI A. NUOH2

1Zoology Department, University of Ghana, Legon, Accra, Ghana;2Ghana Wildlife Society, P.O. Box13252, Accra, Ghana;∗Current address: World Wide Fund for Nature, Avenue du Mont Blanc, GlandCH-1196, Switzerland;∗Author for correspondence (e-mail: yntiamoa@wwfnet.org)

Received 25 August 1999; accepted in revised form 30 September 1999

Abstract. This paper presents data from a twelve-year (1986–98) monitoring of waterbird populations atMuni Lagoon, and discusses the ornithological importance of the lagoon and trends in the use of the site bywaterbirds. The small brackish lagoon forms part of the Muni-Pomadze Ramsar site situated on the Ghanacoast. A total of 48 species of waterbirds were recorded at the site comprising of 29 species of waders,eight species of terns, two species of gulls, seven species of herons and egrets, one species each of duck andcormorant. The most abundant waterbirds species recorded on the site were the Curlew Sandpiper, RingedPlover, Greenshank, Black-winged Stilt, Common Tern, Black Tern, Royal Tern and the Sandwich Tern.Three species of waders, Black-winged Stilt, Pratincole and Little Tern were observed to breed at the site.The highest numbers of waterbirds occurred on the site in the period September to March. The site remainsan internationally important wetland site by virtue of supporting internationally important numbers of fourspecies of terns: Royal Tern, Sandwich Tern, Common Tern and Black Tern. The value of Muni lies morein its use as a feeding/staging site for migrating waders that spend the non-breeding season in Ghana orpass through to winter further south, and as a roosting site for terns which feed mainly at sea. The use ofthe site by waterbirds has increased by some 400% between 1986 and 1998. This is attributed to improvedprey availability resulting from the opening of the lagoon into the sea during the 1994 floods, and reduceddisturbance of feeding and roosting birds. This would imply that the value of the site as waterbird habitatcould improve considerably with appropriate habitat management interventions and continued protection.

Key words: Ghana coastal wetland, seasonal trends, waterbirds

Introduction

The importance of the Gulf of Guinea coast for migratory waterbirds using the EastAtlantic Flyway is well documented (Altenburg et al. 1983; Altenburg 1987; Tyeand Tye 1987; Zwarts 1988; Smit and Piersma 1989; Ntiamoa-Baidu 1991; Schepersand Marteijn 1993; Nicole et al. 1994). However, despite the extensive studies thathave been done on migration and wader populations using this Flyway, Smit andPiersma (1989) identified several major gaps in our knowledge, including lack ofdata on numbers and population fluctuations of waterbirds wintering in coastal areasof West Africa. Since the review by Smit and Piersma, our knowledge on popula-tions of waders wintering and staging on coastal sites in the sub-region has improved

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considerably. The extent of knowledge, however varies: a few large sites are wellknown e.g. the Banc d’Arguin in Mauritania (Zwarts and Piersma 1990; Piersmaet al. 1990) and the Volta Lagoons in Ghana (Piersma and Ntiamoa-Baidu 1995;Ntiamoa-Baidu et al. 1998), while many small sites are relatively unknown.

The Muni lagoon is one of the 13 sites along the Ghana coast which were selectedfor long term waterbird population monitoring under the Ghana Save the SeashoreBirds Project1 in 1986 (Ntiamoa-Baidu and Hollis 1988; Ntiamoa Baidu 1990). In1992, the lagoon and its catchment together with four other sites were designatedas Ramsar sites (i.e. Wetlands of International Importance) on the basis of theirinternational importance for migratory and resident waterbirds (Ntiamoa-Baidu andGordon 1991). The waterbird population monitoring was continued by the GhanaWildlife Society and provides a unique data set for West Africa. Such long-term dataare critical for better understanding of the ecology of the coastal wetlands and theirimportance in the life cycles of migrant waterbirds that use the sites. In this paper,we analyse the importance of Muni Lagoon as a waterbird habitat, and trends in theuse of the site by waterbirds based on count data spanning over a twelve year period(1986–1998).

Survey site and methods

The Muni lagoon, its surrounding floodplains and the adjacent sandy beach on theseafront are located on the outskirts of the Winneba township in the Central Regionof Ghana and constitute the southern portions of the Muni-Pomadze Ramsar Site (seeFigure 2 Gordon et al., this volume). The name Muni was derived from “Boni” inEfutu language which means hard or bitter (personal communication Nana Ayirebi-Acquah, late Chief of Winneba). The lagoon is a shallow, saline, semi-closed coastallagoon, with a surface area of ca. 300 ha. Reports indicate that the lagoon fills upcompletely and spills over to flood the surrounding areas about every ten years duringthe rainy season. At such times, the villagers dig a canal to open the entrance to the seaand the excess water is released to prevent inundation of the village houses situatedon the sand-bank between the lagoon and the sea. One such flooding occurred duringthe 12-year bird survey period in 1994. The lagoon is heavily fished during the leanseason for marine fisheries and also on Tuesdays, which is a “no sea fishing day”.Fishing is forbidden in the lagoon on Wednesdays.

The Muni waterbird surveys were undertaken as part of the waterbird populationmonitoring in key wetland sites along the Ghana coast initiated under the SSBP-G(Ntiamoa-Baidu 1991). Monthly waterbird counts were carried out at the site on oneday in the first half of every month from February 1986 to July 1998 (and is stillcontinuing). The count was done by two to three persons on foot using binocularsand 20×60 telescopes. The survey team would normally start at the eastern bank and

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move northwards to the inlet of the two rivers that feed the lagoon, and then return tocover the southern banks. All species seen were counted and tallied and the total foreach species were pooled at the end of the count.

Results and discussion

Species and numbers of waterbirds occurring on the site

Table 1 gives the list of waterbirds and maximum count of each species recordedat any one time at the site. Forty eight species of waterbirds were recorded at thesite during the 12-year survey. This comprised of 29 species of waders, eight spe-cies of terns, two species of gulls, seven species of herons and egrets, one specieseach of duck and cormorant. Of the waders, only nine species, Curlew Sandpiper(scientific names of all species mentioned in the text are given in Table 1), RingedPlover, Greenshank, Black-winged Stilt, Little Stint, Sanderling, Grey plover, MarshSandpiper and Spotted Redshank, occurred with any degree of frequency. The ninespecies together accounted for 94% of the total of 72 860 wader sightings on the siteduring the survey period. The most commonly sighted species was the Curlew Sand-piper, the species is by far the most abundant migrant wader species recorded on theGhana coast. Another 13 species together contributed 5% of the total sightings. Therarest species on the site (sighted less than ten times throughout the survey period)were the local residents Senegal Thicknee and the African Jacana, and the Palearcticmigrants Dunlin, Eurasian Oystercatcher and Broad-billed Sandpiper. The AfricanJacana and the Eurasian Oystercatcher are not uncommon on the Ghana coast buttend to be restricted to specific sites. For example, over 98% of the total sightingsof Jacanas on the Ghana coast during the 12-year survey came from two sites, Ketalagoon and Sakumo lagoons, while the Oystercatcher was sighted only at estuarinesites with sandy substrate (Ntiamoa-Baidu, unpublished data). The remaining threespecies Dunlin, Broadbilled Sandpiper and Senegal Thicknee are uncommon on theGhana coast.

Five of the eight tern species recorded at the site: Common Tern, Black Tern,Royal Tern, Sandwich Tern and Little Tern occurred commonly. All five are verycommon on the Ghana coast during the non-breeding season (August to April). Thesite also supports the rare Roseate Tern, a total of 925 sightings of the species wererecorded in the survey period, with the maximum recorded at any one time being80 birds. Two other species, the Caspian Tern and Sooty Tern were sighted only onceeach throughout the period, both species are relatively uncommon on the Ghana coast.The most common egret/heron species on the site were Little Egret and Western ReefHeron, both of which are common on the Ghana coast.

The maximum numbers of the different groups of waterbirds recorded at any onetime on the site were 3530 waders, 345 herons/egrets and 16 925 terns. Based on

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Table 1. Waterbird species and relative abundance at the Muni lagoon (1986/98).

Maximum Maximumrecorded at any recorded in % peakone time at entire coastal Ghana

Common name Scientific name Muni counts in Ghana count

WadersEurasian Oystercatcher Haematopus ostralegus 2 45 4.4Black-winged Stilt Himantopus himantopus 475 23 695 2.0Avocet Recurvirostra avosetta 50 3745 1.3Senegal Thicknee Burhinus senegalensis 1 25 4.0Collared Pratincole Glareola pratincola 65 1700 3.8Ringed plover Charidrius hiaticula 640 14 865 4.3White fronted Sandplover Charadrius marginatus∗ 35 500 7.0Kittlitz’s Sandplover Charadrius pecuarius 60 1940 3.1Grey Plover Pluvialis squatarola∗ 210 2060 10.2Senegal wattled Plover Vanellus senegalensis∗ 5 28 17.9Knot Calidris canutus 35 2360 1.5Sanderling Calidris alba∗ 485 4840 10.0Little Stint Calidris minuta 425 21 580 2.0Curlew Sandpiper Calidris ferruginea 1700 52 135 3.3Dunlin Calidris alpina 2 8 25.0Black-tailed Godwit Limosa limosa 50 4295 1.2Bar-tailed Godwit Limosa laponica∗ 30 480 6.3Whimbrel Numenius phaeopus∗ 35 290 12.1Curlew Numenius arquata 10 358 2.8Spotted Redshank Tringa erythropus 180 13 415 1.3Redshank Tringa totanus 15 450 3.3Marsh Sandpiper Tringa stagnatilis∗ 150 1955 7.7Greenshank Tringa nebularia∗ 870 12 090 7.2Wood Sandpiper Tringa glareola 15 1035 1.4Common Sandpiper Actitis hypoleucos 25 385 6.5Turnstone Arenaria interpres∗ 30 515 5.8Broad-billed Sandpiper Limicola falcinellus 1 20 5.0Afican Jacana Actophilornis africana 1 530 0.2Spur-winged Plover Vanellus spinosus 2 8 25.0

Terns & GullsCaspian Tern Sterna caspia 1 440 0.2Royal Tern Sterna maxima∗∗ 3200 11 405 28.1Sandwich Tern Sterna sandvicensis∗∗ 2230 13 830 16.1Roseate Tern Sterna dougallii∗ 80 1080 7.4Common Tern Sterna hirundo∗∗ 8210 36 735 22.3Little Tern Sterna albifrons∗ 940 6885 13.7Black Tern Chlidonia niger∗∗ 6570 34 420 19.1Sooty Tern Sterna fuscata 1 70 1.4Black-headed Gull Larus ridibundus 3 255 1.2Lesser Black-backed Gull Larus fuscus 20 940 2.1

Herons, egrets & othersBlack Heron Egretta ardesiaca∗ 12 170 7.1Green-backed Heron Butorides striatus 2 530 0.4Western Reef Heron Egretta garzetta gularis 78 1920 4.1

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Table 1. Continued.

Maximum Maximumrecorded at any recorded in % peakone time at entire coastal Ghana

Common name Scientific name Muni counts in Ghana count

Little Egret Egretta garzetta garzetta 269 12 055 2.2Yellow-billed Egret Egretta intermedia∗ 6 40 15.0Great White Egret Egretta alba 16 1860 0.9Grey Heron Ardea cinerea 16 2500 0.6White faced tree Duck Dendrocygna viduata 45 53 130 0.1Long-tailed Cormorant Phalacrocorax africanus 16 1360 1.2

∗ Species occurring in nationally important numbers (5% of the peak total coastal count).∗∗ Species occurring in internationally important numbers.

maximum numbers of each species recorded at any one time, Ntiamoa-Baidu andGordon (1992) estimated total population of waterbirds using the Muni site to bearound 23 000. It is considered however, that the number of bird days spent annuallyon the site provides a better picture of the use of the site by waterbirds. Annual birddays spent at the site by terns and waders ranged from a minimum of 206 000 in the1991/92 season to around 1, 852 000 in 1997/98 season.

Three of the waterbird species known to be partial migrants, the Black wingedStilt, Collared Pratincole and Little Tern, breed regularly at the site, the breedingseason being May to July. The value of the site, however, lies more in its use as afeeding site for migrating waders and as a roosting site for terns which feed mainlyat sea, and/or follow beach seines to the shores.

Relative importance of the wetland as bird habitat

The Muni Pomadze site provides feeding, roosting, breeding and moulting habi-tats for 48 of the 88 waterbird species recorded on the Ghana coast (Grimes 1987;Ntiamoa-Baidu, unpubl. data). Nationally, the Muni wetland is the fifth most im-portant site on the Ghana coast for waterbirds, after the Keta, Songor, Sakumo andDensu Delta Ramsar sites. The site was designated as a Ramsar site on the basis ofthe total waterbird populations supported and the population of Black-winged Stiltthat occurred on the site, based on Smit and Piersma’s 1989 1% criteria estimatesfor waterbirds. At the time of designation, the waterfowl population threshold for asite to qualify for Ramsar designation was 10 000, while the estimated 1% populationthreshold for the Black-winged Stilt was 60 (Mathews 1993; Smit and Piersma 1989).

With increasing availability of data on waterbird populations, these thresholdshave been revised to 20 000 total bird population on a site and the 1% thresholdfor Black-winged Stilt to 1000 birds (BirdLife International 1996). Thus the num-bers of Black-winged Stilt supported by Muni is no longer internationally important.Muni, however, still qualifies as an internationally important wetland by virtue of

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supporting internationally important numbers of four species of terns. These are: theRoyal Tern (1% Threshold, 500; Peak count at Muni, 3200), Sandwich Tern (1%Threshold, 1500; Peak count at Muni, 2230), Common Tern (1% Threshold, 8000;Peak count at Muni, 8210) and Black Tern (1% Threshold, 1700; Peak count at Muni,6570). The maximum count of 80 birds recorded for the rare Roseate Tern is equiv-alent to some 15% of the British and Irish breeding population of the species (Avery1987). The maximum count of waterbirds recorded at any one time at the site inthe twelve-year survey was around 19 000 (recorded in September 1997). There is,however evidence that the site is also used as a staging area by many more birdsspending the non-breeding season further along the south-western coasts of Africa.

Nationally, Muni supports important numbers (defined as 5% of the peak countrecorded at any one time for the entire Ghana coast) of 17 species of waders thatoccur commonly on the Ghana coast (Table 1). In terms of Global importance forterrestrial birds, the site supports 24 species of conservation concern, including 23species restricted to the Guinea-Congo forest biome and one species restricted tothe Guinea savanna biome (Ntiamoa-Baidu et al., this volume). These observationsconfirm the global importance of the site as a bird habitat and justify the need tocontinue the ongoing protective and management activities to ensure the maintenanceof the ornithological value of the site.

Seasonal patterns of occurrence of waterbirds at Muni Lagoon

Figure 1 gives the seasonal patterns of wader occurrence on the site based on month-ly counts over the twelve-year period. The highest numbers of waterbirds occur atthe site during the period September to March. Wader numbers at the site begin toincrease with the influx of migrant birds in September. The pattern of occurrencevaried from one year to the other. In some years (e.g. 1986, 1989, 1990 and 1991),numbers increased rapidly to a peak in the period October to December and thendropped rapidly, leaving very small numbers on the site through the northern winterand spring. In other years (e.g., 1988, 1995, 1996), numbers remained relatively highup to March/April. The peak month for waders also varied from year to year. Peaknumbers occurred in December in four out of the 12 years, in January or February intwo of the years and once in September, October, November and March. The lowestcounts were recorded in the period May/June to July. The proportion of waders re-maining on the site during the northern summer months varied from a minimum ofunder 1% to a maximum of around 9% of the peak autumn count. Common specieson the site during the northern summer months are the Black-winged Stilt, Pratincole,Whimbrel, Grey Plover and Greenshank.

The pattern of tern occurrence at the site is similar to that of waders in termsof time of arrival of migrant terns and period of maximum tern occurrence on thesite. However, unlike the wader species that remain on the site all day feeding/roost-ing, terns used the lagoon mainly for roosting. The greater proportion of terns would

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Figure 1. Seasonal patterns in occurrence of Waders at the Muni lagoon.

normally leave the roosting sites on the lagoon (islands within the lagoon) at dawnto feed at sea and return to the roost after dusk. Only small numbers of terns remainon the lagoon during the daytime, in particular small numbers of Black terns and

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Little terns may be seen feeding in the lagoon during the day. On days of intensivefishing activity along the beach, large numbers of terns follow the fishing nets andare attracted to the beaches as the nets are pulled ashore. Numbers of terns roostingon the site and tern activity along the beach therefore fluctuate greatly depending onthe fishing activity going on along the beach and time of count. As such, day-timecounts do not reflect the true numbers of terns using coastal sites in Ghana (Ntiamoa-Baidu 1988). Seasonal patterns of tern occurrence on the site are therefore presentedas “likelihood of tern occurrence” on the site based on the monthly occurrence in thelast ten years of study, expressed a fraction of 1 (Figure 2). There is a 50% likelihoodof finding 200 terns on the site in eight months of the year, August to March, with thehighest chance in August to December. The likelihood of finding a 1000 terns on thesite reaches 50% in only two months of the year, September and December, and thereis a 10 to 30% likelihood of finding 5000 terns at the site in the same period. Thepeak period of tern numbers at Muni is clearly the months of September to January.

Herons, egrets and other species of waterbirds occurred in relatively low numbersand do not present as clear seasonal patterns as terns and waders. The Little Egretand Western Reef Heron occurred in low numbers at the site throughout the year, butslight increases in numbers were observed in some years in October to December andin April/May.

Trends in the use of the Muni lagoon by waterbirds

Figures 3A and B present the inter-year differences in the use of the Muni lagoonby waders and terns over the 12 year period from July 1986 to June 1998, basedon the total number of bird days on the site in each year. The figure shows clearlythat the use of the Muni site by waterbirds has increased several times fold since thebeginning of the survey and there is indication that the increase is continuing. Thenumber of days spent on the site by waders dropped between 1987/88 season and1989/90, then remained stable through to 1993/94 season, increasing sharply fromthen on to a level in the 1997/98 season which was over twice the 1987/88 peak. Thenumber of tern-days at the site remained fairly stable, showing only slight fluctuationsfrom the 1986/87 season up to 1994/95, and then rose very sharply in 1995/96 andcontinued to rise up to the 1997/98 season when the total number of tern-days spentat the site was some 400% the numbers recorded in the early years of the survey. Theincrease in the use of the Muni site by waterbirds may be attributed to several factorsincluding:

(i) Global increases in waterbird populations. The waterfowl population estimatesproduced by Rose and Scott (1997) is perhaps the only global attempt to estimatewaterbird populations and trends. Most population studies tend to be limited to spe-cific sites and/or individual species and focus mainly on breeding success, with veryfew studies on long term population trends. The indications, however are that thetrends are variable, several species are decreasing, others show stable or fluctuating

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Figure 2. Likelihood of tern occurrence at the Muni lagoon.

numbers, while a few species show slight increases in numbers (Smit and Piersma1989; Gunther 1999; Mawby 1999). Of the species of waterbirds occurring com-monly at the site and for which data are available for the East Atlantic Flyway

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Figure 3. Inter-year differences in the use of the Muni lagoon by waders (A) and terns (B).

population, the Ringed Plover, Grey Plover, Black-winged Stilt and Sandwich Ternare increasing, Curlew Sandpiper, Greenshank, Little Stint, Sanderling, Royal Ternand Black Tern are stable, while the Little Tern is decreasing (Rose and Scott 1997).

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Thus the increases observed in numbers of birds using the Muni site are unlikely tobe attributable to global increases in waterbird populations.

(ii) Decrease in the health of the major coastal wetland sites on the Ghana coast(e.g., Keta Lagoon, Songor Lagoon, Densu Delta etc.), resulting in a shift in some ofthe birds using those sites to sites that are normally less productive. A large portionof the Densu Delta Ramsar site on the outskirts of the city of Accra has been lost inthe recent past as a result of housing developments and expansions in the salt miningindustry that initially covered only a small portion of the site. There is, however,no evidence of decline in the numbers of waterbirds using this site (Ntiamoa-Baidu,unpub. data).

(iii) Improvement in the health of the Muni lagoon in terms of water characteris-tics and availability of invertebrate prey items. The results of limnological and aquaticinvertebrate studies carried out at the site in 1993, and more recently in 1997 tend tosupport this. Surveys carried out in 1994 showed that the lagoon was hypersaline (sa-linity values up to 165h) with practically no invertebrate life (Gordon 1994). In June1994 the lagoon and its surroundings were flooded with subsequent breaching of thesandbar in July which allowed exchange between the lagoon and the sea resulting inre-colonisation of the lagoon by invertebrate species. A recent survey shows reducedsalinities and greatly increased invertebrate counts of over 30 000 specimens per m2

(Gordon and Ankrah 1999). Increasing prey availability would certainly attract morefeeding waders and would explain the increases in the use of the site by wading birds.

(iv) Increased protection of the site. The Ghana Coastal Wetlands ManagementProject (CWMP) was established in 1993 to manage five coastal Ramsar sites withfunding from the Global Environment Facility. Site rangers were deployed to theMuni Ramsar site in 1994 and spent a considerable amount of time on protectiveactivities in an attempt to stop wader and tern trapping at the site. Prior to the estab-lishment of the CWMP, there had been considerable educational activities carried outby the Save the Seashore Birds Project-Ghana. The villages along the Muni beachwere included in the key target sites for intensive education when in August 1987,we found a fisherman who had been trapping terns for several years and had 33 met-al rings and 9 colour rings which he used as a bracelet and also for decorating hishair braids. It is possible therefore, that the observed increases in use of the site bywaterbirds is due to increased safety for feeding and roosting birds as a result of theincreased awareness and increasing effectiveness in the protection of the site.

We attribute the observed increases in waterbird use of the Muni lagoon to a com-bination of increased food availability and reduced disturbance at the site. The en-richment of the benthic and fish fauna as a result of the opening of the lagoon tothe sea in the 1994 floods would benefit some waterbird guilds more than others.Waterbird guilds that would benefit in this case would include visual surface-forag-ing, tactile surface-foraging and pelagic foraging waders, as well as herons, whichfeed mainly on invertebrates and fish (Ntiamoa-Baidu et al. 1998). The increasedprotection and related decrease in human disturbance at the site would benefit both

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waders and terns. These observations would imply that the value of the site as wa-terbird habitat could improve considerably with continued protection and appropriatehabitat management interventions. One such intervention which has been advocated(e.g., Tumbulto and Bannerman 1995) is the creation of a permanent opening to thesea. This would reduce the high salinity that characterise the lagoon in the dry seasonand facilitate exchange of life forms between the lagoon and the sea, resulting inincreased prey availability for birds and improved fisheries in the lagoon.

Acknowledgements

The long-term waterbird monitoring undertaken on selected coastal sites in Gha-na was initiated in 1986 as part of the research activities under the Save the Sea-shore Birds Project-Ghana (SSBP-G), and is continued by the Ghana Wildlife Society(GWS). The support of the Royal Society for the Protection of Birds (RSPB UK) forthe SSBP-G initially, and currently for the GWS is gratefully acknowledged. Theauthors are grateful for the assistance of Messrs. David T. Daramani and SamuelAdu, of the Ghana Wildlife Society, for their assistance in the bird counts at varioustimes in the survey period.

Note

1The Save the Seashore Birds Project was a collaborative venture between the Ghana government, theRoyal Society for the Protection of Birds, UK and BirdLife International, established to protect sea- andshorebirds and their coastal wetland habitats.

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