ENDELEO
 
 
 
 
 
 

 

CASE STUDY 7: Elephants’ ranging behavior in relation to vegetation quality: preliminary observations
by Festus Ihwagi and Iain Douglas-Hamilton
 Save the Elephants (www. savetheelephants.org)


Since 1998, Save the Elephants (STE) has monitored elephants’ movement in Laikipia, Samburu and Isiolo districts through GPS and GSM tracking. Several elephants have been tracked at different times and for varying durations within the decade.  It was hypothesized that the distances walked by elephants is related to vegetation quality. Three Samburu matriarchs Sera, Jerusalem and Monsoon have been tracked for 37, 51 and 36 months respectively, with fixes recorded at one hour interval. Tracking data were split into monthly sections and total distances walked were calculated taking into account only months with complete tracking data. The vegetation dynamics were derived from ten day interval NDVI from the SPOT-VEGETATION sensor. This data was obtained from ENDELEO for the entire study period. The values were temporally smoothed with an algorithm inspired by BISE (Viovy e.a., 1992).  It inspects each pixel’s profile and removes all abrupt local minima (supposedly clouds), as far as they don’t persist longer than 4 decades.
To match the monthly sets of tracking data, the average NDVI values of each of three corresponding decades were calculated. Pearson’s correlation was used to test for the correlation between mean monthly track lengths and mean monthly NDVI for Samburu District.

There was a positive correlation between NDVI for each of the most habitat types and distances walked by the elephants in Samburu (see table 1). Figures 1 until 3 graphically show this positive relation for the three Samburu elephants. The variation in NDVI and the corresponding distances walked by Jerusalem (figure 1)are given for the period from March 2003 until November 2009, for Monsoon (figure 2) from March 2001 until September 2005 and for Sera (figure 3) from Oktober 2006 until Oktober 2009. The dotted lines denote the separation of datasets of different collars deployed on them.    

                        Table 1. Correlation coefficients between distances walked by the three elephants and NDVI values for different vegetation types.

Vegetation type

Jerusalem

Monsoon

Sera

all classes*

0.734

0.426

0.644

closed woody

0.793

0.297

0.738

open woody

0.725

0.415

0.667

closed shrubs

0.744

0.369

0.716

open shrubs

0.726

0.428

0.633

herbaceous

0.703

0.429

0.593

(* The category “all classes” takes into account other less important vegetation types in
                     addition to the ones listed.)

casestudy7_1

Figure 1. Variation in NDVI values and corresponding distances walked by Jerusalem. The dotted line denotes the separation of datasets of two collars deployed on her.

<img src="images/casestudy7_2.JPG" width="858" height="364" />

Figure 2. Variation in NDVI values and corresponding distances walked by Monsoon. The dotted lines denote the separation of datasets of three collars deployed on her.

<img src="images/casestudy7_3.jpg" width="853" height="398" />

Figure 3. Variation in NDVI and corresponding distances walked by Sera.

The result of the preliminary analysis gives the motivation to refine the mean NDVI values to exact areas walked by elephants for a better understanding of its influence on elephant movements.  While it is noticeable that the elephants respond to vegetation quality; it should be borne in mind that other factors like surface water distribution influence their ranging patterns too. From an ecological perspective, the major determinants of elephant distribution are availability of surface water (as a primary factor) and then other factors comes in like NDVI. Refining the NDVI to actual area trodden by elephants would hopefully disentangle the actual influences of vegetation quality and surface water on elephants.

This understanding may contribute to a sustainable wildlife management plan. From STE’s long term monitoring of individually recognized elephants, it is known that elephants have limited home ranges during the dry season. In a place like Northern Kenya where surface water is very limited, elephants spend the dry seasons chiefly on the riverside forests along river beds where they get food from. Elephants have a coarse diet and extensively feed on the trees via debarking and felling to access palatable twigs. The bar is probably the richest source of proteins of all forage items and thus no wonder that elephants can survive on it during the dry season. After taking in such a coarse diet, they have to quench their thirst at nearby more permanent sources of water. It is in such dry times that the biggest damage to the riverside forests is immense because they over utilize the woody vegetation. The resultant degradation of forest cover is detrimental to other wildlife species and undoubtedly has a negative effect on future regional climatic conditions.

For questions related to this topic, please contact Festus Ihwagi (Ihwagi@gmail.com) or the ENDELEO helpdesk.


 

 

 

 <Back to top> <Back to case studies>

News
Nov/Dec 2010
Final workshop in Nairobi
October 2010
Download Newsletter 6
May 2010
DEMO Endeleo in Nairobi
April 2010
Smoothed graphs available
March 2010
° Download Newsletter 5
° Case studies elaborated by users
February 2010
NEW in image viewer: toggle on/off borders
January 2010
Help desk available


Related Links
 
Feedback
In order to further improve this website, we would like to know your opinion. Please fill in the feedback form.