Elephant distribution and density within the Associated Private Nature Reserves as derived from GPS-telemetry data

Transcription

1 Elephant distribution and density within the Associated Private Nature Reserves as derived from GPS-telemetry data Steve Henley Save the Elephants South Africa December 2009

2 This brief report was produced in response to a request from the Scientific Committee of the Associated Private Nature Reserves (APNR) for maps of elephant density within the four Private Nature Reserves (Balule PNR, Klaserie PNR, Umbabat PNR and Timbavati PNR) that constitute the APNR. Because the use of these density maps will depend on the objectives defined by the needs of the APNR Reserve Managers, we have not focused on the interpretation of these maps. However, in addition to these maps the report presents additional information and maps that place the telemetry data in its appropriate spatial, temporal and social context to assist in their relevant interpretation. This report is divided into six sections each with one or more associated maps: 1) collaring locations and the spread of telemetry data over time; 2) the demographics of the APNR elephants and the extent of their distribution data; 3) the distribution of bulls and cows within the APNR; 4) the distribution of senior adult, adult and subadult bulls within the APNR; 5) density plots of cows, senior adult bulls, adult bulls and subadult bulls within the APNR; 6) seasonal utilization distribution plots of the study animals. Save the Elephants South Africa (STE-SA) reiterates its commitment to working with the APNR for the effective conservation of elephants and their habitat. The STE-SA biologists are available to assist the Reserves in the use of these data and addressing future issues.

3 1. Temporal spread of telemetry data and study area The first four collars deployed by Save the Elephants (STE) in South Africa were fitted to four bulls in the APNR in 1998 and 1999 as part of the development and testing of GPS tracking technology. However, of these one collar downloaded spurious co-ordinates and the other three functioned for less than four months. Because these data provide only a partial picture of the study animals' range use pattern and not a true reflection of their distribution in response to the changing austral seasonal cycle they not included in this review. The first collar deployed as a direct consequence of the current STE research programme was fitted in May Since 1998 STE has fitted GPS collars to 52 elephants within the Great Limpopo Transfrontier Park: 33 within the APNR, 7 in eastern Kruger National Park (KNP) and 12 in northern KNP. Fig. 1. STE collar deployment timeline covering the period May 2002 to December Study animals are assigned a unique identification code according to their intial collaring location and sex. Those within the APNR have a TKF (Timbavati-Klaserie female) or TKM (Timbavati-Klaserie male) prefix. Eastern KNP elephants are all males and given a KEM prefix. Northern KNP elephants are KNF or KNM for cows and bulls respectively May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec TKM05 Mac re re re TKF01 Diney re re TKM06 Classic re TKF02 Joan re TKM07 Al re TKM08 Benjamin collar removed TKF03 Mandy re TKM09 Barry TKF04 Umbabat re TKM10 Soshangane re TKM11 Brazen collar recovered in the field, assume dead TKM15 Striburus TKM16 Tussle TKM17 Caughley TKM18 Everest shot as a problem animal TKF08 Lapajuma TKM19 Gower TKM20 Proud TKM21 Wessa TKM22 Mellow TKM23 Captain Hook TKM24 Snap collar recovered in the field TKM25 Iain shot as a problem animal TKM26 Namaste TKF09 Koeleria re TKM27 Vee collar removed TKM12 Intwadamela by TEMBO re TKM13 Matambo by TEMBO re TKF07 Summer by TEMBO re KEM01 Mbiri KEM02 Tercievo KEM03 Mune KEM04 Quinto KEM05 Tsevo KEM06 Nkombo KEM07 Nhungu KNM01 Mapimbi KNF01 - Sarita KNF02 Nwankwimbi KNF03 Mangala KNM02 Gila KNM03 Nwambi KNM04 Bvekenya KNF04 Agnes KNF05 Colleen KNF06 Zingi KNM05 Mondli KNM06 Jabulani This report focuses on the data from the APNR study area. However we have excluded the bull TKM05 - Mac, who although initially within APNR is essentially a KNP east bull which moves into the APNR for the few months in the year when he is musth. As such his behaviour and distribution are more representative of elephants from KNP east than the APNR. Map 1. The location of the three STE-SA study areas with the Great Limpopo Transfrontier Park and the 63 collaring events since within the Associated Private Nature Reserves (APNR), 7 in eastern Kruger National Park (KNP - east) and 12 in northern Kruger National Park (KNP - north). Collaring events include the recollaring of study animals and the redeployment of collars removed or recovered from elephants.

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5 2. Demographic and spatial spread of the data Twenty-eight elephants (excluding TKM05 Mac) have been monitored within the APNR study area since May Study animals were chosen to provide a representative spread of the primary demographic groupings of an elephant population. Elephant herds are typically structured along the matriarchal line and are relative cohesive and stable within this, at least in the time frames of this study. For this reason the herd is a single study unit, rather than the individual cow. To monitor the herd we a reproductively active female, and as such cows are all classified as adults. Bulls on the other hand behave more independently and so we refined the age classes to reflect biologically stages in their life history. Table 1. The sex, age and sample size of APNR study elephants as at December ID Name Sex Age class Data points (n) Data points in APNR TKF01 Diney female adult (86.8%) TKF02 Joan female adult (28.9%) TKF03 Mandy female adult (86.8%) TKF04 Umbabat female adult (97.7%) TKF07 Summer female adult (88.7%) TKF08 Lapajuma female adult (93.5%) TKF09 Koeleria female adult (99.0%) TKM06 Classic male senior adult (93.6%) TKM07 Al male adult (54.2%) TKM08 Benji male adult (28.1%) TKM09 Barry male adult (69.0%) TKM10 Shoshangane male sub-adult (93.0%) TKM11 Brazen male senior adult (85.7%) TKM12 Intwandamela male senior adult (37.4%) TKM13 Matambu male adult (85.2%) TKM15 Striburus male sub-adult (96.5%) TKM16 Tussle male sub-adult (38.3%) TKM17 Caughley male adult (95.5%) TKM18 Everest male adult (93.5%) TKM19 Gower male senior adult (99.3%) TKM20 Proud male adult (95.0%) TKM21 Wessa male adult (36.9%) TKM22 Mellow male senior adult (12.3%) TKM23 Captain Hook male adult (11.3%) TKM24 Snap male adult (93.2%) TKM25 Iain male senior adult (33.8%) TKM26 Namaste male immature (68.0%) TKM27 Vee male senior adult (81.7%) Map 2. The distribution of GPS derived data points from elephant cows (n = ) and bulls (n = ) by STE within the APNR study area for the period May 2004 to December 2009.

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7 3. Distribution data within the APNR cows and bulls Almost 70% of the data points recorded by the Timbavati-Klaserie elephants fall within the APNR. The cows recorded a greater percentage of data points (79.9%) within the Private Reserves than the bulls' (66.5%). Data from these collars have been recorded at different intervals (5hr and hourly) at different stages of the project. To ensure the data are not weighted in favour of individuals or periods with frequent records (24 plots in a day as opposed to 5) we have standardised all data sets to a 4-5 hour interval. This represents an event schedule, allowing time between feeding, resting and drinking events within a day and reducing the probability that consecutive data points are autocorrelated. Sample sizes are large enough to provide a realistic measure of the elephants' distribution. As such we can directly interpret these data without having to apply a statistical technique to compute probability distributions, such as the kernel method to interpolate range use and fill in the gaps between data points. Map 3. Distribution of Timbavati-Klaserie elephant cows and bulls within the APNR. Data are recorded at a 4-5 hour interval (cows n = ; bulls n = ).

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9 4. Distribution within the APNR - senior bulls, adult bulls and sub-adult bulls Elephant bulls are grouped into four age classes: immatures, sub-adults, adults and senior adults. Immature bulls are still closely associated with their natal herd, typically less than years of age. Due to their close association with the herds their distribution is not considered further in this report. Sub-adult bulls are younger than 25 years of age. These animals are largely independent of their natal herd but too young to experience musth. Adult bulls, 25 to 35 years old, may have a number of episodic musth events of relatively short duration within a year. Senior adult bulls are large individuals, older than 35 years of age, that typically have an annual musth cycle with a single, extended musth period in a year. Map 4. The distribution of Timbavati-Klaserie elephant bulls within the APNR according to the following age classes: senior adult bulls (n = ), adult bulls (n = ) and sub-adult bulls (n = ).

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11 5. Density within the APNR cows, senior bulls, adult bulls and subadult bulls Density typically refers to the number of records per unit area. As a unit area we have used a 300m x 300m grid system which is aligned with the UTM grid (36S, WGS84 datum). This was chosen as a relevant scale for the following reasons: 1. it is large enough to accommodate the potential error associated with an uncorrected GPS record and so we are confident the data point lies within the appropriate grid cell; 2. in our experience it is large enough to contain a typical behavioural event (eg feeding patch, drinking/bathing area and resting site) while being small enough to differentiate between areas where these events may take place; 3. it is slightly smaller than the average distance between hourly data points (x = 360m; SD = 0.45; n = ) offering the choice for an animal to remain in the same area or move between grid cells; 4. it conforms to the FAO global landcover classification system and is larger than the resolution of most remote sensing images and DEM models enabling us to incorporate these data and their diversity in a habitat model. Visually, the plot density distributions tends to emphasise areas of high density which stand out as darker areas, however the underlying data used for analyses are not biased in this way. Map 5. Elephant density distribution within the APNR derived from the number of 4-5 hour interval location records within a given grid cell. The colour of grid cells is graduated from no records (clear) to high density (dark). The range in values for each sex-age class are: cows: 0 27; senior adult bulls: 0 42; adult bulls: 0 56; sub-adult bulls: 0 56.

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13 6. Seasonal distribution cows, senior bulls, adult bulls and subadult bulls Season is an important driver of savannah ecosystems and as such we include a plot of the elephant distribution data according to season. We have accommodated two seasons: the wet (November to March) and the dry May to September). The transitional months (April and October) have been discarded as they are by definition variable and of less predictive value. Seasonal distributions incorporate fewer data points than the plots and so are defined using the local convex hull (LoCoH) method, also known as the presented as nearest neighbour convex hull (Getz et al PloS ONE 2:e207). This is a non-parametric kernel method that constructs a utilization distribution from the union of convex hulls associated with each distribution point and its k-1 nearest neighbors. The method performs better than traditional kernel methods when fitting utilization distributions to home ranges with distinct boundaries (e.g. fences, lakes). Isopleths reflect the proportional density of points within the polygon. The 100% isopleth includes all data points. The 90% isopleth defines the typical home range without exceptional movements. The 50% isopleth is typically taken to define the core home range and the 10% isopleth highlights hotspots within the home range. Map 6. Seasonal elephant distributions within the APNR as defined by adaptive-locoh plots. The 100%, 90%, 50% and 10% isopleths are shown, each defining a progressively darker ploygon.

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