Spotted hyaena (Crocuta crocuta) feeding ecology and selectivity of large herbivorous prey in the Namib Desert
Fester, Karl (2022), Spotted hyaena (Crocuta crocuta) feeding ecology and selectivity of large herbivorous prey in the Namib Desert, Dryad, Dataset, https://doi.org/10.5061/dryad.w3r2280px
We have investigated the relationship between spotted hyaenas in the south Namib Desert and large herbivorous prey, and have summarized an updated overview of predator-prey relationships in this resource-limited arid environment. Over the 52-month study, we recorded the densities (#/km-2, + SE) of the four local large herbivorous prey species: gemsbok (1.229, + 0.50), springbok (1.352, + 0.48), ostrich (0.648, + 0.23), and greater kudu (0.343, + 0.00). A faecal analysis was performed on 146 collected spotted hyaena scats, and prey items were identified and hairs cross-follicle analysed to the species level. Spotted hyaena diet at the study area remained opportunistic with 240 identified prey items representing eight differing prey species being recorded, ranging from ostrich eggs to large ungulates. The Ivlev’s Electivity Index was used to determine which large herbivorous prey was most selected for. Although gemsbok had a higher representation of prey items in the sampled scats, all sampled large herbivorous prey species scored below 0, and are thus generally avoided in relation to their availability in the environment. If any prey preferences are expressed by spotted hyaena in the Namib, it can be presumed to be a non-sampled prey species. We therefore promote further detailed investigations into all other prey species present, and seasonal variations of prey densities and scat sampling, within the study environment.
Prey species density collection and processing:
Large herbivorous prey species densities were recorded by line-transect game census counts, performed twice weekly by open-backed vehicle at a speed between 25-40km/h and for a consecutive duration not exceeding 2.5hrs. A total of 508 transects were driven at lengths between 23 and 34km (mean=28.96km) using 100m sighting increments with the maximum sighting distance limited to 1,500m due to the openness of the environment and accuracy of measuring distances with a rangefinder. These transects used roads which traversed the entirety of the study area and allowed for sampling within all present landscapes and terrains.
Animal spotting was undertaken employing between five and ten volunteer observers per count, and only individuals or animal groupings within the borders of the study area were recorded. A perpendicular distance was recorded for each sighting by the two main authors on every census using a radial compass and a rangefinder. Due to a lack of game fences and confinement of the sampling area, means were calculated at the end of each sampling month for each species’ group size and perpendicular distances, and a base species density per km-2 was estimated using Distance 7.3 software with parameters of the sampling area.
Scat data collection and processing:
Spotted hyaena scats were collected between December, 2017 and March, 2020. A reference library of hair samples representing ten local wildlife species (gemsbok, kudu, springbok, klipspringer, black-backed jackal, polecat, bat-eared fox, yellow mongoose, aardwolf, and spotted hyaena) and five domestic species (cattle, sheep, goat, donkey, and horse) was created. Prey hair samples were opportunistically collected at the beginning of the study from local species’ carcasses when found in the field, as well as provided by local owners of domestic livestock.
Hikes to locate spotted hyaena scat were conducted twice weekly with five to ten volunteer observers walking several metres apart side-by-side. Distances hiked were between three and twelve kilometres, with an average 500m perpendicular viewing distance from ground level. Hikes were conducted from terrain or man-made features towards open areas, or visa-versa, as well as along the edges of terrain features and, when possible, following water course-ways and game trails up into elevated terrain. These transects were conducted throughout the study area and were non-consecutively re-walked at least three times during the study.
Scats were collected in individual sealable plastic bags, dated, and numbered. A maximum of three scats were collected from latrine sites and selected depending on the varying states of decay to represent the diets over the chronological use of each site. Scats were collected across a range of colourations; greener colouration represented recent scats (within two weeks) while those bleached white through to the core represented older, oxidized scats (up to one year). The outer appearance of the scat (e.g. firm or crumbling outer appearance) was also taken into account in determining the age of the scat collected.
Motion-sensor cameras were placed at each latrine site to confirm the hyaena species using the latrine. Spotted hyaena scats were differing slightly in size and spatial distribution within a latrine from brown hyaena, so differentiation between the two hyaenidae species could be determined. Careful identification during collection through descriptive and photographic references was undertaken, the possibility of misidentification of isolated scats outside of latrines remained, and this was accounted for by collecting only larger-mass isolated scats and avoiding those scats found in the general vicinities of where brown hyaena had been seen on the motion-sensor cameras.
Once collected, samples were air dried for a period of 30 days, and then finely crushed to extract hairs and biological artefacts such as bone fragments, ostrich egg fragments, and feathers. The crushed samples were then dissolved in clear water in fine-mesh cloth to further clean and extract hair samples. Samples from all hairs of differing size, shape and colour were extracted from each dissolved sample. Once dried, these samples were placed onto a microscope slide, numbered according to date and location, and secured under a cover slide. A microscopic cross-follicle analysis was performed against the hair reference library under a magnification of 160 (4/0.08 – 10/0.025) with an 8x eyepiece. Focus was given to the size and shape of the cuticle, and shape of the hair root during the cross-follicle analysis. Identification to the species level of all collected prey items from the scat was attempted.
Due to limitations in available equipment, gravimetric consistencies of prey items per scat were not recorded. Scat was not collected on a seasonal basis, as scats of varying ages were sampled for this dataset.
For the prey density dataset, greater kudu population data was not always consistantly available due to a low presence of the species during data collection.