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Browsing by giraffe in heterogeneous savanna

Mahenya, Obeid John
Doctoral thesis
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URI
http://hdl.handle.net/11250/2433057
Date
2017
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  • Ph.d.-avhandlinger i anvendt økologi / PhD Dissertations in applied ecology [17]
Abstract
Understanding foraging behaviour of wild animals is an important step for wildlife management

and conservation and for learning the animal’s role in the ecosystem. I used Maasai giraffe

(Giraffa camelopardalis tippelskirchi Matschie) as a study animal to see how foraging decisions

of giraffe varied in three study sites; Arusha National Park , Mikumi National Park and Serengeti

National Park, Tanzania, with focus on Arusha National Park (from here on referred to by

names). My focus was on how giraffe make foraging decisions matching the vegetation in a

heterogeneous savannah. I set up the following specific questions; (i) does selection criteria

differ with hierarchical scales?, (ii) how do giraffe browse in relation to the trade-off between

intake rate and quality selection (iii) which activities are most important for giraffe, and how and

why do activities vary in time? (iv) do foraging decisions differ between sexes and

environments? Visual observations were used to collect data on foraging behaviour in both dry

and wet seasons in the year 2013 and 2014. In the first study, our results showed that in Arusha

occurrence of Acacia xanthophloea was the main determinant of foraging decisions used by

giraffes across all scales. In the second study in Arusha giraffe fed mainly from spinescent trees,

such as Acacia xanthophloea, giving lower intake rate than the spineless trees, but assumed to be

nutrient-rich. The third study, also in Arusha, focused on how giraffe allocated time into

different activities, and found that time spent on feeding, resting and socializing was influenced

by season but did not relate to each other. The fourth study compared sexual segregation in

giraffe between Arusha, Serengeti and Mikumi, and focused on whether foraging decisions of

giraffes differ between sexes in the nutrient rich and nutrient poor environments. We found that

female and male foraging patterns were influenced by variation in tree chemistry and differences

in the competing herbivore communities.
 
For viltforvaltning, bevaringsbiologi og for å lære ulike dyrs rolle i økosystemene er det viktig å

forstå deres spiseatferd. Jeg har brukt Maasai giraffer som studieobjekt for å studere giraffers

spiseatferd i 3 nasjonalparker i Tanzania: Arusha, Mikumi og Serengeti, med hovedvekt på

Arusha nasjonalpark. Jeg har studert hvordan giraffer velger hva de spiser i forhold til den

tilgjengelige vegetasjonen i heterogene savanner. Jeg har satt opp følgende problemstillinger: (i)

vil valg av spiseatferd avhenge av romlig skala fra regioner, landskaper, vegetasjonspatcher og

helt ned til en enkelt plante; (ii) hvordan velger giraffer mat avhengig av spisefrekvens og

kvaliteten på maten; (iii) hvilke aktiviteter er viktigst for giraffer, og hvordan og hvorfor varierer

aktiviteter i tid; og (iv) er det forskjell i spisemønsteret mellom kjønn og miljø. Data ble samlet

gjennom å observere giraffers spiseatferd både i tørke- og regntiden, i 2013 og 2014. I Arusha

foretrakk giraffene den tornete Acacia xanthophloea på alle romlige skala. Kvistene spist var

større, og giraffene hadde dermed også en lavere spisefrekvens enn for mange andre plantearter

uten torner. Tid brukt til å spise, hvile og sosialisere, var først og fremst avhenig av årstid – tørkeog

regntid. Begge kjønn valgte beiteplanter forskjellig i næringsrik og nøringsfattige savanner.

Den sterke preferansen for Acacia xanthophloea, spesielt hos hunner, i den mellomrike Arusha

nasjonalpark skyldes at det der var en lav tetthet av giraffer.
 
Description
PhD in applied evology, Evenstad
Publisher
Høgskolen i innlandet

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