i Jean-Marci Duplantier and Daniel Rakotondravony Abstract In Madagascar the rodent problem is linked to one species, the black rat (Rattus rattus). This chapter will describe its population dynamics in agro-ecosystemsand its impact in agricultural crops, in stored grain, on human health and on the endemic rodent community. The black rat has spread absolutely everywhere: from sea level to more than 2,000 m-in houses, fields and also in the forests. It represents more than 95% of rodent catches in the fields and inside houses. Reproduction of rats living in fields stops during the cold season when their maximum annual abundance is observed. Irrigated rice crops suffer the greatest damage with losses estimated at 2.5% of the harvest. Rodent damage is also important for pluvial riceand to a lesser 'fi-- degree for cassava, sweet potatoes and tomatoes. Damage to cacao and sugar I cane are important only in the small, poorly-maintainedpersonal plantations. Plague ,I is undeniably the most important disease linked with rodents in Madagascar. It is endemic to the centre of the island in rural areas located above 800 m and its 5: prevalence is increasing. Rodent control in Madagascar is extremely complex because of the economic difficulties facing the country and because the black rat has displayed such successful colonisation in absolutely all habitats. Keywords Black rat, conservation biology, Madagascar, plague, rice fields, rodent control, rodent damage ! In : <( Ecologically-based rodent management $h. - Eds : Grant Singleton, Lyn Hinds, Herwig Leirs and Zhibin Zhang ACIAR editions, septembre 1999 'h, c 441 o 1O026038 Ecologically-based Rodent Management INTRODUCTION years ago. Significant immigration occurred only 1,000 years ago. The human settlers are of both Asiatic (Indonesian) and African N MADAGASCAR,the rodent origin. A mountain range, 2,800 m high, problem is clearly linked to one divides the island into two from north to I species, the black rat (Rattus raffus), south (Figure 1).The east side of the country and concerns both agriculture and public is more abrupt than the west. The effect of health, as well as conservationbiology. the monsoon and the trade winds on this Eruptions of rat populations were reported relief determines the different climates and in 1916,1932 and 1965 (Rakotomanana 1965; different types of vegetation within the Ravoavy 1966; in Zehrer 1999). After the last island. Human activities have significantly eruption, black rats were declared a public changed the vegetation and now the calamityby the Malagasy state, and different climatic regions can be agricultural pest management of rodents characterised by their agricultural became state-controlled. With respect to landscapes. public health, the major disease problem is The east coast of Madagascar has no dry undeniably the plague (caused by the season and rainfall ranges from 2,000 to bacillus Yersìnia pestis). It spread from the 3,000 mm per year. The original type of seaports of Madagascar at the end of the last vegetation is rainforest. This type of forest is century and during the past 70 years in rapid regression, due mostly to 'slash- permanent rural foci have existed in the and-bum' agriculture. The centre of the- Ir central part of the island, above 800 m. island, called the highlands, has a high Another major issue is that Madagascar's altitude, tropical climate characterised by a endemic rodents are threatened with cold and dry season from May to October extinction as a result of competitionwith the and a hot, rainy season from November to black rat in addition to habitat loss. This April. Before human settlement, it was a chapter will examine how this situation mosaic of forests-savannah. Today, the arose, and describe the impact of the black landscape is totally modified by people, rat in agricultural fields, in stored grain, on dominated by rice-growingin the valleys human health and on the endemic rodent and by dry farming-on the slopes (mainly community in Madagascar. corn and cassava). The primary forests are Madagascar is the fourth largest island in extremely rare, but there are plantations of the world (after Greenland, New Guinea and pin$and eucalyptus. The drier, west coast is Borneo), with a surface area of 587,000 less populated, and is a mixture of square km.It is 1,600 km long from north to cult&vationand pasture. The south is semi- south and 580 km at its widest point. It has aridkith a 10 month dry season, dominated been separated from the African continent by spiny bush. It is a cattle-rearing region for 160 million years. The minimum distance with some small patches of cultivated land. to Africa is now 300 km. The first human settlements occurred approximately2,000 442 Rodent Problems in Madagascar Y NU t plague areas <200m 200-500m 1 500-1 OOOm >1 OOOm 120km Figure 1. Map of Madagascar: relief, localisation of plague foci, main towns and study sites. 443 Ecologically-based Rodent Management COMMUNITY THE RODENT IN the catches in the capital, Antananarivo MADAGASCAR (Rakotondravony1992), which is situated in the centre of the island, and today it has At least 23 species of rodents exist today in reached nearly 95% (Duplantier et al., Madagascar (Rakotondravonyand unpublished data). Recently, we trapped Randrianjafy 1998).Like all animal and plant some individuals in rice fields on the east groups on the island, this order is .coast, several km from the cities. characterised by a high rate of endemism. The house mouse is commonly found in All the endemic rodents belong to the same houses but is less numerous than the black sub-family, Nesomyinae, which is divided rat. It is also found in rice fields, savannas into 8 genera and 20 species. They live and swamp edges, but in low numbers. The almost exclusively in the forest and their date and method of its settlement of current distribution is limited to the Madagascar is not known. remaining primary forests. Brachyiiromys raniirohitra and Nesomys ..lfus are captured The black rat could have come to on farmland but only where this is close to a Madagascar with the first immigrants forest (Rakotondravonyand Randrianjafy approximately2,000 years ago, however its 1998).The destruction of primary forests in presence is confirmed only from the 11th Madagascar, well illustrated by Green and century from excavations of an Islamic Sussman (WO), threatens the extinction of a archaeological site in the north of great number of animal species. It is Madagascar (Rakotozafy 1996; Radimilahy particularly the case for endemic rodents of 1997).The shrew Stincus murinus, native to the Nesomyinae sub-family: not only do all Southeast Asia, must have settled in a of them live in the forests and will therefore similar way. Today, the shrew is found all suffer from habitat loss, but the over the island, but it is less abundant than fragmentation of these forests makes it easier the black rat. The black rat has spread for the highly competitiveblack rat to everywhere.It can be found from sea level to penetrate into the forest. Today, it is more than 2,000 m-in Kouses, fields and common to encounter this species in the also in the forests. In the highlands and in primary forests (Goodman 1995). the middle-west, R. rattus represents more In Madagascar, populated areas are the than 98% of rodent catches both inside and exclusivi domain of three introduced outside buildings (Duplantier et al., species, &e black rat (R. raftus),the Norway unpublished data). Rats$nanosika (1995) rat (Rat& norvegicus) and the house mouse quoted the same figure Gom the east coast (Mus musculus). R. noruegicus has the most coconut plantations. In the fields of the restricted distribution-it is only found in coastal regions of Tulear (south-west) and the seaports and the big cities. It has been Tamatave (east), Rafanomezana (1998a) located in the seaports since the 1930s, but found 97% of rodents to be R. rattus. In the the date of its spread to the highland cities is natural forest of Andranomay, in the unknown (Brygoo 1966). At the beginning of highlands, R. ratfusrepresented two thirds the 1980s, it represented more than 80% of of captures from 1981 to 1982 and the 444 Rodent Problems in Madagascar endemic genus Eliurus only one third Reproduction of the black rat (Rakotondravony1992). At the edge of the forests and within fields at Important studies have been undertaken Andranomay, Rakotondravony (1992) recently on the endemic rodents which are monitored the reproduction in the black rat the most threatened order of mammals in over two years (1981-1982) (Figure 2). Madagascar (Goodman1995). However, due Reproductionbegins before the rainy season to their restricted distribution and scarcity, (Novemberto April) with the maximum they are of minor importance to agriculture number of pregnant females occurring in the and probably also to human health. middle of this period. These data have been confirmed recently: in 1996-1997 there was an interruption to reproduction in the fields POPULATION OF THE BIOLOGY from May to August, with maximum BUCK RAT reproduction in January (Rafanomezana It is a paradox that the black rat is the 1999). number one problem of agriculture and In Mandoto, reproduction of rats living in public health but little research has been houses does not seem to be linked with conducted on this species. Different survey season (Figure 3; Rahelinirina and programs have been conducted by the Duplantier 1999). However, among the rats Department of Plant Protection (Ministry of trapped outside, no reproduction occurs Agriculture), but most of the results are still between July and December-thereafter unpublished except for some data on breeding increases until May and ceases reproduction (Rafanomezana 1999).In fact, abruptly in June.