Alison J. Leslie

Diet of the Nile Crocodile (Crocodylus niloticus) in the Okavango Delta, Botswana

Abstract The analysis of stomach contents can shed light on patterns of prey availability and foraging habits of a predator; however, recent studies have shown the potential bias in dietary studies resulting from differential digestion rates of various prey items. The stomachs of 286 Nile Crocodiles (17–166 cm snout–vent length) were lavaged over a two-year period. Taking prey residence times into account, the contents were examined for prey eaten within 24 h. Crocodylus niloticus has a similar ontogenetic shift in diet to that of other crocodilians. Yearlings consumed primarily aquatic insecta and arachnida. As crocodile size increased (juveniles), the diet became more diverse including crustacea, amphibia, and fish. The largest size class (subadults) consumed primarily fish. Yearlings fed consistently throughout the year; however a higher proportion of empty stomachs occurred within the juvenile and subadult size classes during the winter months. Seven species of nematodes were found within the stomachs, four of which represent new geographic records.

Characterising ontogenetic niche shifts in Nile crocodile using stable isotope (δ13C, δ15N) analyses of scute keratin.

Nile crocodiles undergo a three to five order of magnitude increase in body size during their lifespan. This shift coincides with a change in resource and habitat use which influences the strength, type and symmetry of interactions with other species. Identifying size-specific crocodile groups displaying similar traits is important for conservation planning. Here, we illustrate how stable carbon (δ13 C) and nitrogen (δ15 N) isotope analysis of scute keratin, together with breakpoint modelling analysis can be used to characterise ontogenetic niche shifts. Using a sample set of 238 crocodiles from the Okavango Delta, Botswana (35–463 cm total length), we found prominent size-related changes in the scute keratin δ13 C and δ15 N profiles close to 40 and 119 cm snout-vent length. The first shift corroborated the findings of a traditional stomach-content study conducted on the same population at the same time, and the second conformed to known crocodile ecology. This approach can be used as a first approximation to identify size-specific groups within crocodile populations, and these can then be investigated further using isotopic or other methods.

Physical and Chemical Characteristics of Warthog (Phacochoerus africanus) Meat

The common warthog (Phacochoerus africanus) has been introduced to parts of South Africa outside of its known range. The species is considered an agricultural pest and a threat to the natural environment. As some farmers are employing a shoot on sight strategy, our study aimed to investigate the physical and chemical characteristics of warthog meat according to sex. Five muscles from male warthogs had higher shear force values (i.e. were less tender) compared to females. Allmuscles had a total protein content >20% and total lipid content ≤2.2%. The ratio of polyunsaturated to saturated fatty acids of the Longissimus lumborum muscle was <0.45. We also provide descriptive data on the characteristics of carcass yields and meat from juvenile sows and boars. It is suggested that warthog meat should be produced and marketed as whole muscle cuts and not as the typical commercial cuts used for domestic animals.

Living with predators: a focus on the issues of human–crocodile conflict within the lower Zambezi valley

Context Human–wildlife conflict is a global problem and increasing worldwide as people and wildlife compete for limited resources. Conflict between people and crocodiles, especially in Africa, is recognised as a serious problem. The people of the Chiawa Game Management Area are heavily dependent on the Zambezi River for several resources from potable water and irrigating fields to a source of food (subsistence and small-scale commercial fishing). Aims To assess the spatial and temporal scale of human–crocodile conflict (HCC) and identify associated factors, with a view to recommending mitigation measures. Methods A questionnaire survey and Zambia Wildlife Authority data were utilised to estimate the scale of HCC. Key results Between 2000 and 2009, there were 98 crocodile attacks on people, 62.2% were fatal. Most of the attacks occurred while canoe fishing (57.1%) and collecting water (29.6%). Crocodiles were disliked and seen as a ‘problem’ by the majority of the populace. Even though crocodiles are a charismatic mega-fauna species, being employed within the tourism industry had only a minor positive effect on people’s attitudes. The area is an important location for crocodile egg and adult harvesting, although the local population gains no financial benefit. An increase in the number of boreholes in the villages was suggested by the local people as the primary mitigation measure, as well as the removal of crocodiles by various means. Conclusions Although people displayed an understanding of the risks of crocodile attack, very few actually employed mitigation techniques or utilised protective barriers when at the river. Increased water-access points (and their maintenance) in the villages would reduce people’s dependency on the river. The negative attitude towards crocodiles is an issue that has to be addressed to allow successful implementation of long-term conservation strategies. Implications Understanding local people’s attitudes towards wildlife is an important aspect within any conservation management plan. Competition for limited resources by people and wildlife is guaranteed to cause confrontations. The existing mitigation for human crocodile conflict in Zambia is ineffective. The negative attitude towards wildlife needs to be addressed and a suitable response formulated. The most favoured type of mitigation suggested by local people was more boreholes and the removal of crocodiles. Photograph by Kevin Wallace.

Re‐evaluating the effect of harvesting regimes on Nile crocodiles using an integral projection model

Crocodile populations are size-structured, and for populations that are subject to harvesting, removal is typically size selective. For this reason, size-structured matrix models are typically used to analyse the dynamics of crocodile populations. The boundaries between the size classes used to classify individuals in these models are typically chosen arbitrarily. This is problematic because results can depend upon the number and width of size classes. The recent development of continuous character population models termed integral projection models (IPM) has removed the need to arbitrarily classify individuals. These models are yet to be applied to harvested animal populations. Using information obtained from the literature, we develop an IPM for crocodiles. We use perturbation analyses to investigate how altering size-specific demographic rates influences the population growth rate and the strength of selection on snout to vent length. We find that perturbations can lead to complex responses. Sensitivity analysis to population growth and fertility selection reveals that the smallest animals and the sizes of early breeding individuals and their eggs may have more influence on these population biology parameters than previously thought. Although our model is relatively simple, our results show that IPM can be used to gain theoretical insight into the possible consequences of altering size-specific demographic rates on the population and evolutionary ecology of harvested populations.

The influence of season and sex on the carcass yield of common warthog (Phacochoerus africanus)

The carcass yield and dress out percentage of the common warthog (Phacochoerus africanus) was investigated as influenced by season and sex. Season did not have a significant impact on carcass weight (P = 0.64) and dress out percentages (P = 0.28) of adult warthogs (n = 46). Males (n = 21) had heavier carcasses (35.24 kg ± 2.59) than females (n = 25) (27 kg ± 0.96) (P = 0.03) and had a higher dress out percentage (57.14% ± 0.91) than females (52.14% ± 0.91) (P < 0.01). Due to the imbalance in sampled populations age was not included as a variable in the final analyses. Warthogs have a favourable carcass yield and can be utilized for commercial game meat production.

Comparative analyses of the chemical and sensory parameters and consumer preference of a semi-dried smoked meat product (cabanossi) produced with warthog (Phacochoerus africanus) and domestic pork meat

The study compared the chemical and sensory characteristics and consumer preference of a semi-dried, cured meat product, cabanossi, produced with warthog meat and with domestic pork. The warthog and pork cabanossi had similar total moisture (59.0%±2.07 and 54.3%±1.26) and protein (26.3%±2.20 and 24.2%±2.15) contents, while the warthog cabanossi was lower in total fat content (6.9%±1.01) compared to pork cabanossi (13.7%±1.77, P=0.007). Descriptive sensory analysis found that the warthog cabanossi appeared darker red (P=0.001) and less fatty (P=0.001), while the pork cabanossi had a higher overall pork flavour (P=0.001). There were no differences in consumer preference of the appearance and taste between the two types of cabanossi, while the majority of consumers (91%) supported the use of game meat in meat products. The study concluded that warthog meat can be used in processed products without compromising the associated technical or organoleptic properties.

Population size and structure of the Nile crocodile Crocodylus niloticus in the lower Zambezi valley

Concern has been raised about the lack of population data for the Nile crocodile Crocodylus niloticus in the lower/middle Zambezi valley. This area is important for conservation as well as being a source of crocodile eggs and adults for the ranching industry. Two spotlight surveys, in 2006 and 2009, were used to estimate population size, structure and trends. A stage-structured matrix model was parameterized from existing literature and the expected predictions were compared to those observed. The survey data suggests a population increase since 2006. Crocodile density was greatest (3.1 km −1 ) in the areas of increased wildlife and habitat protection and lowest (1.4 km −1 ) in areas of increased human presence. The predicted population stage structure differed to that observed, suggestive of a population not at equilibrium. Data on offtakes of crocodile eggs and adults would be useful for examining why this is the case. Continued monitoring of the wild population is necessary, to evaluate the trend of an increasing crocodile population, and additional demographic data for modelling purposes would be desirable.

Ectoparasites of a Non-Indigenous Warthog Population, Phacochoerus africanus, in the Free State Province, South Africa

A population of the common warthog, Phacochoerus africanus, recently became established on several farms in the Free State Province, South Africa. The aim of the study was to record ectoparasite species that occur on this non-indigenous population and to compare the parasite abundance and prevalence at three different times during 2011. Forty-six warthogs were culled in autumn (15), winter (16) and spring (15). Each individual warthog was screened for ectoparasites for 7–10 minutes by 3–4 persons. Parasites were removed using forceps and stored in 70% ethanol. Ticks were identified by an expert taxonomist, while fleas and lice were identified using published books containing their respective taxonomic keys. A single flea (Echidnophaga larina) and louse (Haematopinus phacocheri) species and three tick species (Hyalomma truncatum, Rhipicephalus gertrudae and Rhipicephalus simus) were recovered from 46 warthogs. The louse and flea were the most abundant ectoparasitic taxa, while the ticks had lower mean abundances. This is the first record of the tick R. gertrudae on warthogs in South Africa. Temporal variation in parasite abundance was observed. The louse was most abundant during spring and summer, while the flea preferred cooler and drier winter conditions. Hyalomma truncatum and R. gertrudae both preferred warmer spring conditions. In general, parasite species richness in the non-indigenous host population was low, which could support the parasite release hypothesis.

Chemical Composition of African Savanna Buffalo (Syncerus caffer) Meat

African buffaloes (Syncerus caffer) are hunted for their trophies and the meat is seen as a secondary product. Little information exists on the chemical composition of buffalo meat or the effect that sex and muscle type may have thereupon. In the present investigation, eight male and four female buffalo that were found to be positive for tuberculosis (Mycobacterium bovis) were culled and the chemical composition of their meat determined. Although male buffalo meat had higher moisture and protein than females, these differences were small and it is debatable whether a consumer would notice such differences. The amount of fat (<2 g/100g) and ash did not differ between sexes. Similarly, the differences in the proximate composition of the Biceps femoris, Longissimus dorsi and Semimembranosus muscles were all also <1 g/100 g meat. Sex had no effect on the amino acid composition of the muscles but alanine, valine and histidine content differed between muscle types although the differences were <1 g/100 g protein. The fatty acid (FA) composition did not differ between sexes or muscle type. Oleic acid was the dominant FA followed by linoleic and palmitic acids. The FA had similar ratios of saturated FA (∼38%), mono-unsaturated FA (∼31%) and poly-unsaturated FA (∼29%). The low fat to protein ratio and a poly-unsaturated to saturated FA ratio of >0.7 indicates that buffalo meat is a lean, healthy and condensed protein source.