Assessment of the Vulnerable Status of Kinixys homeana (Testudines: Testudinidae) for the IUCN Red List
ABSTRACT
The IUCN Red List status of Kinixys homeana is reassessed using interviews, field surveys, recent and old literature, and extrapolation of local trends (mainly in Nigeria). Available data indicate that numbers have declined drastically in recent years due primarily to habitat loss, hunting, and export for the pet trade. All these threats are still current and probably increasing, and we recommend change in status from Data Deficient to a minimum of Vulnerable A2cd.
Home's hinge-back tortoise, Kinixys homeana (Bell 1827), previously listed as Data Deficient by the IUCN Red List (IUCN 2003; assessed in 1996), was reassessed for its threatened status in 2003 and subsequently accepted for listing by IUCN as Vulnerable (IUCN 2006). This report formed the basis for the listing change.
Taxonomy
Order: Testudines. Family: Testudinidae. Scientific name: Kinixys homeana. Species authority: Bell, 1827.
Taxonomic Comments
All populations are considered to be homogenous and no subspecies of this taxon are currently considered valid.
Common Names
Home's hinge-back/hinged/hinged-back tortoise (E); Kinixys de Homme (F); Stutz-Gelenkschildkröte (G).
Countries of Occurrence
Liberia, Ivory Coast, Ghana, Togo, Benin Republic, Nigeria, Cameroon, Equatorial Guinea, and Democratic Republic of Congo.
Current Population Trends
Decreasing.
Major Threats
Subsistence hunting by local people in desperately poor economic conditions; agricultural and industrial expansion; deforestation; trade for the pet industry.
Previous (2003) Red List Status
DD—Data Deficient, assessed in 1996.
Proposed Red List Status
VU A2cd—Vulnerable.
Historic Distribution
Kinixys homeana is a forest tortoise with considerable range over the continuous Guinea-Congo West Africa rainforest region (Fig 1). The most reliable account of its distribution is provided by Iverson (1992), although comments are available also in later literature (e.g., Vetter 2002). However, for this species as well as for many Afrotropical reptiles, the picture of the distribution is based on an indiscriminate list of all the reliable locality records collected also during the colonial age (i.e., often in areas that have been drastically modified by humans during the last decades). As a result, these maps are often little more than “ideal maps,” a reflection of a species' previous distribution rather than its current status. Because of this, the distribution map of K. homeana (and virtually of all other medium- to large-size vertebrates) is a great overestimation of its real distribution.
Citation: Chelonian Conservation and Biology 5, 1; 10.2744/1071-8443(2006)5[130:AOTVSO]2.0.CO;2
Kinixys homeana is found in Liberia, Ivory Coast, Ghana, Togo, Benin Republic, Nigeria, Cameroon, Equatorial Guinea, and in the Democratic Republic of Congo (Fig. 1).
Liberia
Found throughout the country: known in the northwest provinces as well as in the extreme southeast, around Harper (Iverson 1992).
Ivory Coast
Recorded in the forests around Aboisso in the south (Iverson 1992).
Ghana
Reported to be widespread in the southern territories (Iverson 1992).
Togo
No localities are presented in Iverson (1992), but see below.
Benin Republic
No localities are presented in Iverson (1992), but see below.
Nigeria
Found only in the southern regions (Iverson 1992), in the continuous rainforest vegetation zone.
Cameroon
Found throughout the coastal regions and also in the Southern Province (Iverson 1992); its presence has also been well documented in the Southwest Province in recent years (e.g., Lawson 1993, 2000, 2001).
Equatorial Guinea
Found both on Bioko Island and in Rio Muni (Iverson 1992).
Gabon
Not recorded by Iverson (1992), but likely present because of a very few specimens exported in recent years to international markets.
Congo Kinshasa
Isolated populations are known from the easternmost forests, close to the political borders with southern Sudan and western Uganda (Iverson 1992). These populations should be accurately studied to understand whether they are an isolated subspecies or typical homeana.
Present Range
Liberia
No recent survey on the distribution of this species in Liberia has been published. Several specimens (>50) were found by our research staff in the bush-meat markets of Monrovia, Buchanan, and Gbarnga during July 2000. According to the sellers, the tortoises were captured in the nearby surroundings. We also captured (and marked) 14 specimens in the coastal forest around Greenville, in July 2002, during a period of 8 consecutive days of research (a total of 68 hours spent in the field). Kinixys homeana is reported by villagers to be locally common (e.g., around Gbarnga), and the pilot surveys in Greenville established an average sighting frequency of 1.75 tortoises/day, which is intermediate between those observed in southern Nigeria in i) a harvest area (0.84 tortoises/day) and ii) a nonharvest area (2.98 tortoises/day) (Luiselli 2003a). Based on interviews with local hunters and on our preliminary data, we believe that Kinixys homeana is still widespread in Liberia, although likely declining due to overexploitation by people. In particular, Liberia's recent civil war has had serious consequences for several populations of this species. Kinixys homeana became a common food item for people displaced into forests or bushlands to escape the fighting. Indeed, several interviewees confirmed that tortoises were one of the main protein sources not only for people escaping war but also for soldiers operating in forested zones.
Ivory Coast
No recent surveys made by ourselves or associates. Historical records (summarized in Iverson 1992) showed that it is found only in the south.
Ghana
Kinixys homeana has been found recently in Onyadze and Ony-Winn (two sites of Muni-Pomadze Lagoon, southern Ghana) in secondary forest and grass/thicket habitats (Raxworthy and Attuquayefio 2000). Our staff did not capture any free-ranging specimens of this species during pilot surveys conducted in 1995, 1996, and 1998 in the coastal bushland in the Great Accra region, but we did capture a single male in a bush-plantation area around Cape Coast (southwestern Ghana). Additional surveys in October–November 2003 in the markets around Accra and Koforidua (southern Ghana) indicated several specimens traded, and a very few specimens found in the field (which would likely mean a very low population density; see Table 1). Based on data provided by Raxworthy and Attuquayefio (2000), plus our surveys (and from comparisons with other geographic regions such as Liberia and Nigeria), and on interviews with local people, we consider this species to have become increasingly uncommon in Ghana. The numbers of free-ranging tortoises captured for the international pet trade should also be monitored, because it cannot be excluded that, as in Togo (Harris 2001), many traded specimens do not come from tortoise farms.
Togo
Found only in the remnant forests around the towns of Kpalime and Badou (southwestern Togo) (Harris 2001).
Benin
Although no records are available in Iverson (1992), the species is certainly present in Benin Republic, where it is heavily exploited (Table 1) and also exported to western countries (Table 2).
Nigeria
The current distribution is well known because the species has been studied intensively by ourselves and associates during the last ten years (e.g., Luiselli et al. 2000, 2003; Luiselli 2003a, 2003b, 2003c, 2005). This species has been observed by our staff in several states:
Lagos: presumably rare; several specimens were only found in the forest fragments and bush around Maryland and Lekki Lagoon.
Oyo: presumably declining (according to several interviewees); we found it in the forest patches around Ibadan, where it has been collected also in the past (Blackwell 1968), and is actively hunted (Butler and Shitu 1985).
Edo: locally common in mature forest fragments, but presumably extirpated from the many recently deforested areas. Based on random surveys throughout 13 potential sites of occurrence in 1999–2000, we verified its presence in only 4 sites (30.8%).
Delta: very endangered due to severe habitat loss (potential habitat for tortoises covers approximately 0.1% of the state area) and hunting for subsistence. For instance, it was found along the riverine swamp-forests of the Etiope River in 1982, but not found again in 2001 (Lea et al. 2003).
Bayelsa and Rivers: found in some swamp-forest patches of both these states (e.g., Powell 1993; Luiselli et al. 2000) and is locally common in a few areas where it is worshipped by indigenous communities (Luiselli 2003a). However it is actively persecuted for both subsistence and traditional medicine (“ju-ju”) in most areas, where it is very likely to be declining (see data in Luiselli 2003a). In addition, it is severely threatened by habitat loss (deforestation) due to expanding petrochemical development.
Anambra: extremely rare, it is found only in a few riverine forest patches in the southernmost part of this state and surrounding Oguta (in AGIP oil-field forest site). Most of the state landscape is characterized by plantations and cultivations, not suitable habitat for this tortoise.
Akwa-Ibom: severely fragmented populations are found in a few riverine forests (e.g., along the banks of the River Kwa-Ibo) and in the Stubbs Creek Forest Reserve; many specimens are traded for “ju-ju” and food in Uyo market, but it seems that a good proportion of them may have come from the adjacent Cross River State (Eniang, unpubl. data). In addition, it is severely threatened by habitat loss (deforestation) due to petrochemical expansion in coastal areas. More common at the border with Cross River State (surroundings of Itu).
Cross River: common in lowland forests (e.g., in the Ikpan Forest block, see Eniang and Luiselli 2002), it is replaced by Kinixys erosa in hilly and mountainous forests. In the Cross River National Park, for instance, it is much less common than K. erosa, but this is probably due to natural ecological constraints.
Cameroon
No recent surveys made by ourselves or associates. Lawson (2000) reported very strong hunting pressure on this species in the Western and South-West Provinces. Lawson (1993) recorded its presence in 7 different sites (Abat, Mundemba, Baro, Besingi, Ekundu Kundu, Pamol Palm Plantations, Nfainchang). Additional known localities are Bipindi, Dibongo, Jengwe, Kribi, Déhané, Nkolembembe, Nko'olong, and Akom II (van Dijk 1994; LeBreton 1999).
Equatorial Guinea
No recent surveys made by ourselves or associates.
Gabon
No recent surveys made by ourselves or associates. Its distribution is unknown but likely extremely reduced (for instance it was not found during two very extensive field surveys in the Monts de Cristal and in the Massif du Chaillu; see Pauwels et al. 2002a, 2002b), although very few specimens were traded and exported (Table 2).
Congo Kinshasa
No recent surveys made by ourselves or associates.
Habitat Preferences and Current Habitat Status
Most of the data available on the habitat preferences of K. homeana populations are based on anecdotal observations and not on sound data. It is reported that this species occurs in forests throughout its range, generally of a drier type than the forests inhabited by K. erosa (Ernst and Barbour 1989). According to Broadley (1989) it inhabits the lowland evergreen forest, and a similar habitat has been described in western Cameroon (Lawson 1993), where it is locally threatened by clearance of forest for cultivation (e.g., around Nfainchang; Lawson 1993).
The most detailed study on the habitat preferences of K. homeana was conducted in southern Nigeria. At a landscape scale, a statistical study (based on logistic regression of presence/absence data) revealed that Nigerian populations of K. homeana are habitat specialists, being linked to zones of secondary dry forest around mangroves and in zones with secondary swamp-forest (Luiselli et al. 2000). Considering that in the Delta states these habitat types have declined dramatically during the last decades, falling from 2% of state area in 1976–1978 to only 0.2% in 1993–1995 (Geomatics 1996) due primarily to petrochemical expansion, it may be inferred that habitat loss represents a very serious reason of decline for these tortoises at a global scale. This supposition is reinforced by evidence that K. homeana needs closed forest canopy and shady microhabitats to avoid overheating, and shows behavioral thermoregulation in its avoidance of overheating (Luiselli 2005), i.e., allowing only short periods of exposure to the sun during movements between sunlit and shaded areas (Hailey and Coulson 1998; Luiselli 2005). Another potential limiting factor for habitat occupancy by K. homeana may be a potential for interspecific competition for food with the closely related K. erosa, which exhibits a wide overlap in terms of spatial use (Luiselli 2003b).
At a local scale, Luiselli (2003a) demonstrated that the type of attitude of human communities towards tortoises may have very serious consequences on the habitat preferences of these animals, so that any generalization can be difficult. Luiselli (2003a) studied tortoise population ecology at six study areas with similar habitat characteristics in the eastern axis of the Niger Delta. In three areas, the tortoises had been worshipped by local communities for a long time as holy animals, whereas in three other areas, they were actively hunted for subsistence. The habitat use by tortoises varied depending on the type of treatment by the indigenous people (hunting vs. veneration): in the veneration areas the tortoises were frequently found in disparate habitats (i.e., dense dry bush, sparse dry bush, riparian vegetation, swamps, and plantations; Luiselli 2003a). In the hunting areas, the tortoises were found almost exclusively inside dense bush, and always avoided plantations. It seems likely that the different habitat usage reflects extirpation from easier hunting areas (Luiselli 2003a). This study may have important global consequences for this species' status because it demonstrates that wherever they are hunted for subsistence (which is a common occurrence in West and Central Africa, e.g., see Fa et al. 2000; Lawson 2000; Fa and Garcia Juste 2001; Luiselli et al. 2003), the habitat in which they are still found is just a fraction of the potential habitat. They are limited to forest patches with very dense vegetation where access for human hunters is difficult. Forest habitat loss is an enormous problem in West Africa because of the rate of destruction (Oates 1999), and concomitant with this, human overpopulation and increasing hunting pressure (e.g., Luiselli 2003a, c; Luiselli et al. 2003) means that the long-term viability of these tortoises is at high risk.
Clearance of forest for cultivation is also considered a cause of decline for K. homeana in Cameroon (e.g., around Nfainchang; Lawson 1993). Although we do not have quantitative data for other countries, it is obvious that the same is happening almost everywhere in the range of this tortoise, since in all these countries human population density is growing, forest loss is rapid, and hunting for subsistence is rampant (e.g., see discussion in Oates 1999).
Extent of Occurrence
According to our calculations, based on maps in Iverson (1992) modified by data reported in other sources published before 1992, and on original data made available to us (referring to distributions in 1980–1990), the entire range of K. homeana had a potential extent of occurrence of about 788,443 km2 in 1992 (Table 3). The country comprising the highest percentage of the potential range was Nigeria (23.4%), followed by Cameroon (20.3%).
Because Nigeria and Cameroon comprise the greatest proportion of this species' potential range (43.7%), they are appropriate to assess the current global status of K. homeana in the absence of firm data from the other countries.
Area of Occupancy
Because few fieldwork-based data on the area of occupancy exist for K. homeana, the area of occupancy is simply defined as 10% of the area of extent of occurrence as applied in the Red List Criteria (IUCN 2001), yielding an estimate of 78,843 km2. In Nigeria, where the human population density is expanding rapidly (currently about 120 million people) and where the remnant proportion of forests is very low (about 1% of that found in the 1950s; Geomatics 1996), it is almost certain that the current tortoise range is far less than the 10% of former range expected according to IUCN (2001) criteria. We would suggest that a more appropriate estimate of the current range of K. homeana in Nigeria is approximately 5% of that in 1992 (i.e., approximately 9235 km2, and this is certainly an overestimation). A current occupation of only 5% of the 1992 range would translate to an assessment, for the Nigerian populations, as Critically Endangered by IUCN criteria A2c. Of course, this does not include reduction in occupancy in other range states, and so we could not be sure about the soundness of any generalization of this assessment as CR. However, it has not been reported anywhere that the species survives significantly better in other countries, and there is little cause for optimism. Hence, based on these calculations, the status of K. homeana is clearly becoming vulnerable due to the considerable extent of habitat loss in addition to subsistence hunting.
Population Size and Density
There are no available data on the global population size and density of K. homeana at the continental scale. We therefore need to use the few data available on the density and home ranges of these tortoises from some specific localities to generate estimates of population size at the continental scale.
In the Niger Delta (southern Nigeria), during 1995–2002, we radiotracked 33 adults (20 males and 13 females) for 40 continuous days, and measured mean home range size (quantified via minimum convex polygon) of 0.37 km2 for males and 0.24 km2 for females, with some specimens (especially males) exhibiting home ranges as large as 0.46 km2. Lawson (2000) also stated that, in western Cameroon, male home range may exceed 0.5 km2; his data were very similar to our own despite the different study regions and environmental conditions. Moreover, both in Nigeria (Luiselli and Associates, unpubl. data) and in Cameroon (Lawson 2000), male tortoises are highly territorial and usually drive other males away from their core home ranges. Thus, the density of these tortoises is low in most places, even in highly suitable environments. Luiselli (2003a) presented some data on population structure and abundance of K. homeana that can be useful for calculating a rough density of these tortoises under natural conditions. During 20 consecutive field days of research in southern Nigeria (10 days in the wet season and 10 days in the dry season, from February 2001 to January 2002) 10 people independently searching a 20-ha area found an average density of 1.4 tortoises/ha at six localities. The density ranged from 0.15 to 0.9 tortoises/ha in harvest areas, and from 1.65 to 2.85 tortoises/ha in veneration areas (density values calculated from Table 1 in Luiselli 2003a).
Kinixys homeana is known to inhabit similar habitats across its entire range, and data from separate regions (Cameroon and Nigeria) showed a clear similarity also in home range size and territoriality. Hence, we may use the above population density of approximately 1.4 individuals/ha for K. homeana in Nigeria to extrapolate estimates for the whole species range. Calculating population size from the population density estimates (Luiselli 2003a), we expect approximately 140 tortoises in an area of 1 km2, which would give a figure of about 1,300,900 tortoises in all of Nigeria according to the most optimistic view (i.e., assuming that in 50% of the occupied sites there is veneration, and no hunting pressure). However, since our data show that veneration occurs in less than 1% of the occupied sites, the total tortoise population figure would be much lower. With an average density (calculated from Luiselli 2003a for harvest areas) of 0.53 individuals/ha this gives 53.33 tortoises/km2, and about 500,000 tortoises in all of Nigeria. This latter figure is probably a much more accurate population estimate. If we apply the above reasoning to the whole of this species' range we calculate a total population size for K. homeana of at best 4,205,000 tortoises.
Lawson (2000), studying the harvest rates of K. homeana in three protected areas of Cameroon (Korup National Park, Banyang-Mbo Sanctuary, Nta-Ali Reserve), estimated an overall mean annual harvest rate of 0.3 animals/km2 in these areas with good habitat conditions and relatively low human density. Then, if 100% of the species' range was protected and under relatively low human density, and extrapolating harvest data by Lawson (2000), the expected annual harvest rate would have been 236,532 tortoises, i.e., 5.6% of the total surviving tortoise population. However, the percent of protected territory is less than 3% of the species' range, and the human population density is much higher in several regions of the species' range than in the three protected areas of Cameroon studied by Lawson (2000), and hence we may conclude that the annual harvest rate is certainly much higher than the calculated 5.6%, but not quantifiable on the basis of current data. Also acknowledging the theoretical limits of our calculations, which are simply estimates, it is still very likely that the free-ranging populations of this species cannot sustain the current pressure (combination of continuing habitat loss and hunting) for more than 2–3 generations (sensu IUCN 2001), with each generation being about 15 years. Based on the above assumption, K. homeana meets at least the IUCN (2001) Red List criteria for Vulnerable status, but a case for an even higher category of risk can be made.
Reduction in Population Size
There are no data on the decline in population size for this species, even at a very local level. Robust calculations are therefore impossible; however, we can attempt extrapolations based on the same type of reasoning as above, again using Nigeria as a benchmark.
Assuming that i) the density of tortoises has remained constant in suitable habitats, ii) local hunting pressure has remained constant over the years (this is very unlikely, given that the human population has grown from about 35 million in 1959 to approximately 120 million in 2001 [Anonymous 1960; Nigeria Population Census 2001]), and iii) the suitable habitat for K. homeana has declined by at least 90% in the last 40 years, then it can be estimated that in 1960 (date of Nigerian independence) there were at least 5,000,000 tortoises in Nigeria compared to the estimate of about 500,000 today. Hence, using these estimates (i.e., a 90% decline in suitable habitat in the past 40 years, translating to a decline of roughly 40% per 10 years), K. homeana can be classified as Vulnerable A2cd according to IUCN (2001) criteria. In particular, if we assume the generation time for this species to be about 15 years, then the three generations to be considered for Red Listing encompasses the entire 40-year period and thus a 90% decline. This would qualify as Critically Endangered by criteria A2cd. Again, this is for Nigeria, not range-wide, but there is no indication that Nigeria represents an exceptionally bad case of decline (apart from its high human population size), more a best-studied case and indicative for most of the region. Similar extrapolations can be performed for the other countries as well, and all these calculations conclude that i) the population decline has been very rapid for K. homeana, and ii) there is no reason to predict that this trend will be reversed or slowed.
Although K. homeana is still found in nearly all the forest-zone protected areas in Nigeria (Table 4) and in Cameroon (Lawson 2000), there is no doubt that hunting is still rampant in all these protected areas, as testified by harvest data provided by Lawson (2000) and the observations of Luiselli (2003c) of hunted specimens inside two protected areas in the Niger Delta. Hence, a crucial point to be addressed by future studies is the impact that illegal hunting activities may have on populations of K. homeana inside formally established protected areas. At present, it is clear that protected area populations are not free from exploitation.
Major Threats and Conservation Measures
Major threats and disturbance factors are listed in Table 5. Conservation measures, both present and those needed, that are realistically achievable within the next five years, are listed in Table 6. Comments on numbered notes from Table 6 are discussed in the text below.
Note (1)
It is important to plan the management of this species by collecting as much information as possible on the cultural interactions between local human communities and tortoises, because it may be possible to create a mosaic of protected areas linking all the forested zones in which people traditionally worship tortoises. This strategy is certainly possible in some areas of southern Nigeria (Bayelsa State), e.g., around the towns of Sagbama and Brass.
Note (2)
Although K. homeana is on CITES Appendix II, thus banning the import of wild individuals into Europe (EC regulation number 338/97), it nevertheless seems necessary to develop further conservation legislation in favor of this species both at the international and national levels. At the international level (IUCN Red List), it seems necessary to list this species as Vulnerable and no longer as Data Deficient; at the national and subnational level, it is necessary to include this species among the protected fauna in all the countries of occurrence. At present, there is virtually no country that can reliably preserve this species, and we have seen several specimens traded for food or traditional medicine even inside protected areas (e.g., Upper Orashi Forest Reserve in Rivers State, southeastern Nigeria). Another serious problem is represented by the high rates of export of these tortoises to western markets from such countries as Ghana and Togo (e.g., see Lawson 2000). The exports of these specimens should be seriously controlled to prevent free-ranging specimens being taken, especially considering that it is often unclear how these specimens are obtained because tortoise farms are very underdeveloped in these countries. Harris (2001), for instance, found that most Python regius exported from Togo to Europe were claimed to come from farms but were actually newborns of wild-caught females (who were killed after oviposition). Close control should be exercised on these farms to prevent the tortoise trade from being conducted in the same way.
Note (3)
The field ecology of K. homeana has been studied intensively only in southern Nigeria and in western Cameroon. These studies should be continued in these two countries to achieve a very detailed dataset, but should also be urgently expanded into other countries of this species' range for comparative purposes. The same is true also for the studies on the relationship between humans and tortoises.
Note (4)
There is a strong need to establish protected areas that include populations of these tortoises, and perhaps a very promising initiative would be to create protected corridors by linking areas where local people traditionally protect tortoises.
Note (5)
Potential attempts at trade management have been undertaken (see Table 2). However, these should be developed more to reduce impact of export trade on wild-caught animals.
Conclusions
It is clear that K. homeana is currently experiencing a very serious decline in much of its range, due mainly to habitat loss and intensive harvesting for subsistence and traditional medicine (“ju-ju”), as well as for the international pet trade. It seems more than likely that these threats will continue to grow in the next five years, due to continuing rates of deforestation, overpopulation, and industrial development in some crucial areas (e.g., southern Nigeria). Therefore, it is warranted to change the Red List status of K. homeana from Data Deficient to Vulnerable. Concerted national and international conservation efforts are needed to save the species from further decline, and it is advised that these efforts must be based strictly on scientific criteria. Consultation with individual specialists and other relevant parties such as the IUCN/SSC Tortoise and Freshwater Turtle Specialist Group are encouraged at all times during the planning and implementation of conservation efforts.
Previously known localities (dots) (from Iverson 1992) and recently discovered sites of occurrence (open circles) of Kinixys homeana in West Africa. Arrows indicate sites of suspected decline or disappearance of this tortoise. Note that tortoises are especially threatened in coastal areas and much of the region remains unsurveyed. The isolated populations of the Democratic Republic of Congo should be studied to verify whether they are identical to the other populations of the species, or if they have diverged to achieve the status of different subspecies or species.
