Pastoralist’s livestock and settlements influence game bird diversity and abundance in a savanna ecosystem of southern Kenya Dana L. Morris1*, David Western2 and David Maitumo2 1
Department of Fisheries & Wildlife Sciences, 302 Anheuser-Busch Natural Resources Bldg., University of Missouri, Columbia, MO 65211, U.S.A. and 2African Conservation Centre, PO Box 62844, Nairobi, Kenya
Abstract We investigated the vegetation structure and density of game birds along a successional gradient created by varying intensity of human settlement in a pastoral community in Shompole group ranch in southern Kenya. We examined four habitat types including heavily-grazed grass in currently occupied settlements, short grass in seasonal settlements, patches of bushed woodland in settlement sites that had been abandoned up to 30 years ago, and tall grass in a wildlife sanctuary. Vegetation biomass was the highest in the sanctuary where livestock are excluded and the lowest in the vicinity of currently occupied settlements. Abundance of doves (Oena spp. and Streptopelia spp.) was best associated with moderate grazing and per cent green grass, which provide good foraging opportunities. Francolin and spurfowl (Francolinus spp.) were positively associated with vegetation biomass. Quail (Coturnix spp.) were positively associated with tree cover. These data reflect the importance of maintaining a balance of wildlife and livestock grazing with patches of ungrazed grasslands and bushed woodlands in providing a mosaic of habitats that support a diverse population of game birds. The results have wide application for an integrated management approach to livestock, wildlife and game bird management in the savannas. Key words: gamebirds, grazing, hunting, livestock, pastoralists
Re´sume´ Nous avons e´tudie´ la structure de la ve´ge´tation et la densite´ du gibier a` plume le long d’un gradient cre´e´ par la *Correspondence: E-mail: morrisd@missouri.edu
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variation de l’intensite´ des installations humaines, dans une communaute´ pastorale dans un ranch de Shompole, dans le sud du Kenya. Nous avons examine´ quatre types d’habitats: l’herbe fortement broute´e dans les installations qui sont actuellement occupe´es, l’herbe courte des installations saisonnie`res, les ˆılots de broussailles dans les anciennes installations abandonne´es parfois depuis 30 ans et les hautes herbes d’un sanctuaire de la faune. La biomasse de la ve´ge´tation e´tait la plus grande dans le sanctuaire d’ou` le be´tail e´tait exclu et la plus basse dans le voisinage des installations encore occupe´es. L’abondance des tourterelles (Oena spp. et Streptopelia spp.) e´tait plutoˆt lie´e a` un broutage mode´re´ et a` un pourcentage d’herbe verte qui donnent de bonnes possibilite´s de se nourrir. Les francolins (Francolinus spp.) e´taient positivement lie´s a` la biomasse de la ve´ge´tation. Les cailles (Coturnix spp.) e´taient positivement lie´es a` la couverture arbore´e. Ces donne´es refle`tent l’importance de conserver un e´quilibre entre les paˆturages de la faune sauvage et du be´tail et des ˆılots non paˆture´s et des broussailles, pour cre´er une mosaı¨que d’habitats qui accueillent une population varie´e de gibier a` plume. Les re´sultats peuvent largement trouver une application dans les approches inte´gre´es de gestion du be´tail, de la faune sauvage et du gibier a` plume en savane.
Introduction Communities over much of eastern and southern Africa are developing new wildlife enterprises in response to the devolution of opportunities and responsibilities for conservation opened up by political reforms and liberalization (Western, 2001). In Kenya, many new ecotourism lodges and private or community-run wildlife sanctuaries have been set aside over the last 10 years, offering a significant scope for conserving biodiversity in non-protected areas
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(Western & Waithaka, 2005). Shompole Group Ranch in the southwestern portion of Kajiado District, southern Kenya, is one of several communities that have developed wildlife enterprises. With the assistance of the African Conservation Center (ACC), Shompole struck a shareholder agreement with a tour operator, Art of Ventures, to build and manage a tourist lodge. In 1998, the ranch community set aside a 10,000 ha wildlife sanctuary for tourism and manages a staff of rangers to monitor and protect wildlife. The sanctuary and tourist lodge generate income for the community. Waithaka et al. (2002) have shown that plant and animal biodiversity has increased across the group ranch since its establishment, offering an important refuge for resident and migratory wildlife. The success of this venture led to the establishment of the Shompole Community Trust, charged among other functions with developing integrated land use plans for livestock and wildlife utilization. The Trust has set up a conservation committee to develop wildlife plans based on sound biological information. The plans will aim to utilize and conserve as much of the area’s rich biological heritage as it can. Like so many pastoral communities throughout eastern Africa, the question is whether livestock production and wildlife enterprises can be integrated successfully. To a great extent, the answers depend on understanding the interactions between livestock and wildlife and exploring ways for them to coexist to the financial advantage of landowners. The purpose of this study was to investigate one aspect of human-wildlife interactions that is poorly understood, namely, the effects of livestock grazing and human settlement patterns on game birds. Game birds hold considerable potential for diversifying and adding to wildlife incomes on community-run lands, but have been given little attention to date. In this study, we looked at the impact of livestock grazing pressure and settlement patterns on vegetation structure and its influence on game bird populations. Specifically, we measured game bird abundance and diversity among four grassland habitats along a vegetation successional gradient created by livestock grazing pressure, ranging from heavily used current settlements to lightly used seasonal encampments, abandoned settlements of varying age, and ungrazed areas in a wildlife sanctuary.
Materials and methods Shompole Group Ranch (elev: 500–1000 m) covers approximately 62,869 ha in the southwest section of the
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Magadi Division, Kajiado District (1 50¢–2 05¢S to 36 00¢–36 10¢E). It is bordered by the Nguruman Escarpment to the west, the rift wall to the east, and the alkaline Lake Natron to the south. The Ewaso Nyiro River bisects the group ranch, feeding a series of swamps in the southern portion of the ranch. Ambient temperatures are high (mean max. 34 C) and rainfall is low and bimodal, averaging 250 mm a year. The soils range from fine lacustrine soils around the swamp margins to stony poorly drained grumosols derived from basaltic rocks. The major habitat types include bushed grasslands, open grasslands and plains, open woodlands, riparian forest along the Ewaso Nyiro, and swamp. The community set aside 10,000 ha in the northwest section of the ranch in 1998 to serve as a wildlife sanctuary where grazing is prohibited except during times of extreme drought. Shompole Group Ranch straddles the rift valley on the Kenya side of the border with Tanzania. It supports a mixed migratory population of large ungulates, which move seasonally between wet season grazing grounds on the short grass plains to the woodlands and swamps bordering the Ewaso Nyiro River in the dry season. The pastoral communities traditionally follow a similar seasonal grazing pattern. The transient nature of pastoralism has a large impact on wildlife and biodiversity generally as a result of shifting livestock grazing pressure and large quantities of nutrients shifted around the landscape by short-lived cattle camps and settlements. Settlements typically consist of six to twelve dwellings surrounded by a protective thorn enclosure. Cattle are corralled within the circle of huts and sheep and goats within inner thorn enclosures. Settlements are occupied seasonally and seldom for more than 3–5 years total (Western & Dunne, 1979). The large dung deposits left in the corrals after they are abandoned has an impact on plant succession for up to a century. The nutrient enrichment effect of abandoned settlements creates islands of fertility clearly visible in the savannas. Plant succession on these nutrient hotspots creates a flush of grass that dominates the first 20–60 years post-settlement, followed by a heavy cover of shrubs and trees (Muchiru, 1992). The impact of shifting grazing and settlement patterns affected by seasonal rains and droughts sets up a mosaic of habitats within savanna ecosystems (Muchiru, 1992) and this is clearly visible in Shompole. Understanding the relationship between these historical patterns and the current grazing practices on wildlife populations is the basis for understanding the interaction of wildlife, livestock and game birds.
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From 7 to 26 June 2004, we surveyed birds and sampled vegetation in four successional habitats that included heavily-grazed grass near currently occupied settlements, short grass near settlements used seasonally, patches of bushed woodland in settlement sites that had been abandoned up to 30 years earlier according to local residents, and tall grass in the reserve or sanctuary. Although some amount of seasonal variation in vegetation structure and bird populations is to be expected, we chose to sample in June, just after the long rains, when most resident species are in breeding plumage, less transitory, and perhaps most detectable. The successional habitats were distributed patchily, driven by shifting patterns of livestock and settlement use over time. The dominant grasses included Sporobolus spp. R. Br., Setaria spp Beauv. and Cynodon dactylon L. Dominant trees and shrubs included Acacia nubica Benth., Salvadora persica L., Grewia spp. L., Cordia gharaf Ehrenb. ex Asch., Cadaba spp. Forssk and Boscia coriacea Paz. We chose seven to eight sites in each of the four habitat types in which to survey birds using 10-min flush counts. At each site, we walked or rode in the back of a pickup truck along two parallel 100 ¡ 50 m line transects separated by 50 m and spent 10-min recording birds seen or heard along each transect. Each sampling site therefore represents 10,000 m2 or 1 ha. The boma itself was included within one of the two transects. Each site was visited three times, twice in the morning between 06.30 and 11.00 hours and once in the late afternoon between 16.30 and 18.00 hours. We sampled vegetation within a 30-m radius plot in a subsample of the sites using a pin frame method following McNaughton (1979). We measured per cent cover, bare ground, green grass, grazed grass and grass height. We calculated total biomass for each 312-m2 plot by using an equation based on ground cover and height (Western & Lindsay, 1984). Within each plot, we divided the circle into four equal quadrats and within each quadrat recorded the number and species of trees and distance to the nearest tree >5 cm dbh. Detection rates or density (birds per ha) of individual species were calculated by averaging the number of detections over three visits to a site. Densities of game birds were evaluated by grouping related species into taxonomic groups. Several species of doves were grouped together (laughing dove, Streptopelia senegalensis; African mourning dove, Streptopelia decipiens; ring-necked dove, Streptopelia capicola; and Namaqua dove, Oena capensis), as they share similar habitat requirements and primarily forage on seeds
on the ground (Urban, Fry & Keith, 1986). Crested francolin (Francolin sephaena), and yellow-necked spurfowl (Francolin leucoscepus) generally scratch for seeds, corms, and insects on the ground (Madge & McGowan, 2002) and were grouped together as francolin for purposes of analyses. Black-faced sandgrouse (Pterocles decoratus) and chestnutbellied sandgrouse (Pterocles exustus) are two closely related species that are primarily ground-feeding birds of scrub and grasslands (de Juana, 1997; Madge & McGowan, 2002). The two species of quail (common quail, Coturnix coturnix; harlequin quail, Coturnix delegorguei) that were grouped together inhabit open to lightly wooded grasslands, tend to prefer thick ground cover, and forage mostly on seeds and invertebrates (Madge & McGowan, 2002). Because of small sample sizes, we were unable to develop and test models for densities of helmeted guineafowl (Numida meleagris). We developed generalized linear models on the basis of competing hypotheses that vegetation structure associated with foraging opportunities, cover, or vegetation biomass best describes variation in bird densities and species richness. A Poisson distribution was specified in all models to account for overdispersion associated with count data. Variables included in the models include % bare ground, % green grass and % grazed grass (FORAGING); distance to nearest tree and number of trees (COVER); and biomass (BIOMASS). We used square root transformations on the dependent variables (except for sandgrouse) to correct for non-linearity or unequal variances. We constructed a global model for each species that included all relevant effects (Table 1) and each global model was tested for goodness of fit against a null model with no effects. The global models fit the data (total, v2 = 16.8, df = 6, P < 0.05, n = 21; doves, v2 = 13.8, df = 6, P < 0.05, n = 21; francolin, v2 = 14, df = 6, P < 0.05, n = 21; grouse, v2 = 21, df = 6, P < 0.05, n = 21; quail,
Table 1 Candidate models for model selection Model
Parameters
GLOBAL
Sqrt (% grazed) + sqrt (% green) + sqrt (% bare) + distance + number of trees + log (biomass) Sqrt (% grazed) + sqrt (% green) + sqrt (% bare) Distance + number of trees Log (biomass)
FORAGING COVER BIOMASS
The same set of models was compared for total game bird abundance and for each species group.
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100
% Grazed
90
% Green
80
% Bare
70 Percent
v2 = 48.8, df = 6, P < 0.05, n = 21). We ran the generalized linear models using the GLIMMIX macro in SAS (SAS Institute, 2004) to obtain maximum likelihood estimates ()2loglikelihood). We then used Akaike’s Information Criterion (AICc for small sample sizes), calculated from the )2loglikelihood value multiplied by two times the number of parameters in each model, to rank each candidate model for each species group. We selected the most parsimonious model with the lowest AICc score and the highest Akaike weight (which is considered the weight of evidence for a particular model, given the full set of candidate models) to use for inference (Burnham & Anderson, 2002). Descriptive statistics such as mean ± SE and 95% confidence intervals are included for several vegetation parameters of particular interest and are estimated from the top models.
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60 50 40 30 20 10 0
Current
Seasonal
Abandoned
Reserve
Fig 2 Per cent grazed, green grass and bare ground in four stages of vegetational succession and human settlement in Shompole Group Ranch, Kajiado, Kenya
Results The vegetation structure of the boma sites varied with the successional stage and intensity of human settlement. Biomass of grasses was the highest in the reserve and at abandoned bomas (Fig. 1), while per cent bare ground and grazed grass was the highest in currently grazed settlements (Fig. 2). The number of trees per plot was the highest in the abandoned settlements and lower in occupied settlements (abandoned, 24.3 ± 2.9; reserve, 9.5 ± 2.2; current, 6.0 ± 1.3; seasonal, 5.3 ± 1.8). We detected sixteen species of game birds including several species of grouse, francolin, spurfowl, quail, doves, bustards and guineafowl. Mean species richness of game birds was the highest in abandoned settlements (Fig. 3), 1200
Biomass (g m–2)
1000 800 600 400 200 0 Current
Seasonal
Abandoned
Reserve
Fig 1 Biomass (mean, dot; SE, box; 95% CI, line) of vegetation surrounding three stages of human settlements: current (n = 8), seasonal (n = 8), abandoned (n = 8); and in a conservation reserve (n = 7)
No. species detected/visit
6 5 4 3 2 1 0 Current
Seasonal
Abandoned
Reserve
Fig 3 Mean species richness per site in three stages of human settlements: current (n = 8), seasonal (n = 8), abandoned (n = 8); and in a conservation reserve (n = 7). Shown are mean (dot), SE (box) and 95% CI (line)
while density of all species combined was the highest in seasonal and abandoned settlements (Fig. 4). However, patterns for each species varied. Dove densities were ten to twenty times higher than all other species (Fig. 4a). Francolin and spurfowl occurred at low levels in grazed habitats and increased sharply in the reserve, whereas quail did not occur altogether in grazed habitats such as current and seasonal settlements (Fig. 4b). Sandgrouse were in relatively low abundance across all sites. We detected no flocks of helmeted guineafowl during point count surveys, but they were occasionally detected in groups of 25–150 individuals in grazed grasslands with heavy shrub cover and widely dispersed trees. Because they congregate in large flocks that are extremely mobile, they are not easily detected by the line transect ⁄ flush method.
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Table 2 Results of model selection describing vegetational differences on density of game bird species
(a) 30 25 No. Birds/ha
Model 15 10 5 0 Current
(b) 2.5 2 No. Birds/ha
)2loglikelihood
K
AICc
DAICc
1.2 13.7 11.02 )1.4
4 2 3 7
11.70 18.37 18.43 21.22
0.00 6.67 6.73 9.52
0.93 0.03 0.03 0.01
6.3 16.4 15.4 4
4 2 3 7
16.80 21.07 22.81 26.62
0.00 4.27 6.01 9.82
0.85 0.10 0.04 0.01
11.3 13.4 19.6 6.6
2 4 3 7
15.97 23.90 27.01 29.22
0.00 7.94 11.05 13.26
0.98 0.02 0.00 0.00
92.7 92 95 96 113.7
1 3 2 4 7
94.91 99.41 99.67 106.50 136.32
0.00 4.51 4.77 11.60 41.42
0.83 0.09 0.08 0.00 0.00
)30.1 )19 )35.6 )18.4
3 2 7 4
)22.69 )14.33 )12.98 )7.90
0.00 8.35 9.70 14.78
0.98 0.02 0.01 0.00
w
20
Seasonal
Abandoned
Reserve
FRANCOLIN FRANOLIN SANDGROUSE QUAIL
1.5 1 0.5 0 Current
Seasonal
Abandoned
Reserve
Fig 4 Mean density of Doves (a) and yellow-necked spurfowl, crested francolin, black-faced and yellow-throated sandgrouse, and common and harlequin quail (b) in three stages of human settlements: current (n = 8), seasonal (n = 8), abandoned (n = 8); and in a conservation reserve (n = 7)
The FORAGING model was the best model predicting the density of all species combined (Table 2). There was a positive relationship between total density and per cent grazed grass (parameter estimate: 0.013 ± 0.003) and per cent green grass (parameter estimate: 0.014 ± 0.003), suggesting vegetation structure limits foraging opportunities for game birds. The FORAGING model was also chosen as the best model for doves (Table 2). There was a positive relationship between dove density and per cent grazed grass (parameter estimate: 0.17 ± 0.05) and per cent green grass (parameter estimate: 0.13 ± 0.03). As per Fig. 4a, doves occur in the highest densities in seasonal or abandoned sites where biomass, per cent grazed and green grass are at moderate levels. The BIOMASS model was chosen as the best model for francolin and spurfowl with an Akaike weight of 0.98 and with a positive relationship between francolin density and biomass (parameter estimate: 0.13 ± 0.04). The NULL model was the best model for sandgrouse, suggesting no effect of the variables, or
Total FORAGING BIOMASS COVER GLOBAL Doves FORAGING BIOMASS COVER GLOBAL Francolins BIOMASS FORAGING COVER GLOBAL Sandgrouse NULL COVER BIOMASS FORAGING GLOBAL Quail COVER BIOMASS GLOBAL FORAGING
)2loglikelihood, maximum likelihood estimate; K, number of parameters; AICc value, for small sample sizes; DAICc, change in AICc value between the model with the lowest AICc and the next best model; w = Akaike weight. Models are arranged in order of highest rank or importance for each species group.
perhaps we failed to measure relevant vegetation characteristics. For quail, the COVER model was the best model with a weight of 0.98 suggesting quail prefer trees interspersed within the grassland (parameter estimate for number of trees: 0.016 ± 0.003).
Discussion The reserve had the highest biomass of grasses and low levels of grazing. Settlement sites that were currently occupied were heavily grazed and had the lowest vegetation biomass. Sites that were used seasonally or had been abandoned for up to 30 years had higher biomass, were lightly grazed, and had less bare ground. Additionally, the
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abandoned sites had higher tree densities and had a more complex vegetation structure with an open canopy of trees, shrub layer, and high grass cover. These vegetation differences are in part because of the dung deposited by livestock on and around settlements, leading to elevated levels of organic carbon, nitrogen, phosphorus, and magnesium for up to 100 years post-occupation (Muchiru, 1992). Muchiru (1992) showed that biomass of herbaceous and grass species increases to a peak up to 20 years after a site is abandoned, at which Acacia tortilis Hayne trees may dominate. Differences in relative abundance between game bird species reflect their diverse life-history requirements. Doves require a mixture of bare ground and short grazed grass for foraging and trees for roosting sites (Goodwin, 1983). This combination of habitats was not specifically modelled. However, variables associated with foraging are included in the top model for doves and their abundance matches closely to moderate levels of bare ground, green, grazed grass (Figs 2 and 4a), and tree density. Francolin and spurfowl rely on ground cover for protection while foraging, nesting, and moving close to the ground, which is indicated by a positive relationship between high biomass and Francolinus spp. abundance. Similarly, others have shown that per cent ground cover and height of vegetation were important factors influencing the distribution and density of yellownecked spurfowl in Kenya (Eves, 1994) and redwing francolin (Franolinus levaillantii) in grasslands in South Africa (Jansen et al., 2001). Similarly, Jansen, Little & Crowe (1999) showed that their densities were limited by grazing intensity and frequency of burning in South Africa. Our data from Shompole reveal no relationships between vegetation characteristics and sandgrouse abundance. In contrast, others have shown that sandgrouse populations seem to be limited by proximity to waterholes in Spain (Ferns & Hinsley, 1995) and annual variations in rainfall in South Africa (Little, Crowe & Villacastin-Herroro, 1996); variables we did not measure. As an interesting aside, Njoroge et al. (1997) showed that black-faced and chestnut-bellied sandgrouse breeding seasons correlate closely with patterns of rainfall and seedset in Kenya. Njoroge et al. (1997) also showed that hunting seasons in southern Kenya overlap with breeding seasons of sandgrouse (but not other species) from July through October. However, if proximity to water sources and dependency on rainfall limit sandgrouse, it would be advisable for wildlife managers to consider hunting seasons that are disjunct from the rains and sandgrouse
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breeding seasons in southern Kenya to maintain healthy viable populations. Quail were not detected in more heavily grazed habitats such as current and seasonal settlements. COVER was the best model related to their abundance, suggesting that they were attracted to areas with high biomass and close proximity of tree cover, which is indicated for harlequin and blue quail, but is not typical of common quail, which prefer open grasslands (Madge & McGowan, 2002). Unlike highly mobile species like sandgrouse and doves, many species of quail and francolin may require feeding, roosting, cover, dusting, nesting and brooding sites within a small range. Additionally, natural high mortality of nests and hatchlings caused by predation and drought keeps productivity of these species low (Brennan, 1994; also see Elphick, Dunning & Sibley, 2001; Urban et al., 1986). Therefore, we suggest maintaining areas with a mosaic of habitats with high biomass of grasses interspersed with trees and moderate grazing to maximize quail productivity. However, populations will probably vary significantly on an annual basis, given fluctuations in local rainfall and migratory movements that are not well understood. It appears that shifting locations of settlements in space and the high turnover of new and abandoned settlements over time is a major factor influencing the heterogeneity of habitats, and in turn the diversity and abundance of game birds on Shompole Group Ranch. Our results concur with several recent studies that have demonstrated the importance of a matrix of diverse habitats for gamebirds (Dorgeloh, 2000; Ratcliffe & Crowe, 2001; Jansen & Crowe, 2002). Maintaining the mix of habitats, current bird diversity and their resilience to droughts will, therefore, depend heavily on continued seasonal movements of livestock and rotational use of settlements. As the seasonality and flexibility of livestock in the face of patchy rainfall and episodic drought are the key to production and survival of pastoral economies (Western & Finch, 1986), there is good reason to retain flexible grazing and corral patterns in future group ranch management plans. Such flexibility will not only retain the resilience of pastoral herds in arid lands such as Shompole, but also reduce competition with wildlife and expand the prospects for wildlife income. Shompoleâ&#x20AC;&#x2122;s 10,000 ha wildlife sanctuary associated with a lodge and camping grounds has already diversified the communityâ&#x20AC;&#x2122;s livelihood and generated significant revenues. Furthermore, the wildlife sanctuary can double as a grass bank for livestock during harsh times, adding to their drought resilience.
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The income and resilience the Shompole community derives from a mixed and shifting pattern of livestock and wildlife use stands to gain further from game bird management. As we have shown, this pattern of land use naturally lends itself to a diverse and abundant game bird population. Game birds could, therefore, be managed within an integrated livestock and wildlife management framework based on habitat management and drought resilience. Without further evaluation of population densities in Shompole, conservative harvest rates of 25% of coveys or standing densities are recommended for francolin, spurfowl, and quail (Little & Crowe, 1993; Simiyu & Bennun, 2000). It will be necessary to separate hunting from breeding seasons (in association with local rainfall) to maintain a diverse and healthy population of game birds. This could be done on the basis of an integrated monitoring program incorporating game bird assessments with counts of livestock and wildlife population numbers and distributions in relation to habitat and range conditions.
Acknowledgements We thank members of the Shompole Group Ranch for allowing us to conduct this study and for providing information about the history of settlements and J. Mungee for organizing meetings with local residents. We also thank P. Porneluzi and an anonymous reviewer for helpful comments on the manuscript. This project was funded by the African Conservation Centre.
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