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The mi­gra­tion sea­son in the Maa­sai MaraSerengeti re­gion in Africa has be­gun ear­lier than usual this year, due to the de­struc­tion of habi­tats

Down to Earth - - CONTENTS - MAINA WARURU | NAIROBI

Maa­sai Mara's wilde­beest have be­gun their sea­sonal mi­gra­tion ear­lier this year as their habi­tat gets frag­mented due to hu­man ac­tiv­i­ties, dis­rupt­ing tra­di­tional mi­gra­tory pat­terns

THE MAA­SAI Mara-Serengeti re­gion, span­ning across the bor­ders of Kenya and Tan­za­nia, has been a the­atre to the great wilde­beest mi­gra­tion for thou­sands of years. An es­ti­mated 1.5 mil­lion wilde­beest or gnus, ze­bras and gazelles as well as many species of large African her­bi­vores mi­grate across the Mara river an­tic­i­pat­ing rains and in the pur­suit of fresh pas­tures and wa­ter.

This year, how­ever, the mi­gra­tion of an­i­mals from the Serengeti Na­tional Re­serve in Tan­za­nia to the Maa­sai Mara Na­tional Re­serve in Kenya be­gan ear­lier than usual— in June. The mi­gra­tion usu­ally starts in July and ends in Oc­to­ber. Tourist op­er­a­tors are sched­ul­ing the African sa­faris much ear­lier. In eastern and south­ern Africa, frag­men­ta­tion of habi­tat has oc­curred along with the de­cline in the abun­dance and geo­graphic range of an­i­mals. For ex­am­ple, in north­ern Tan­za­nia, there has been a grad­ual loss of con­nec­tiv­ity between sea­sonal ranges avail­able to mi­gra­tory wilde­beest. This has led to fluc­tu­a­tions in the abun­dance of an­i­mals.

Such changes in mi­gra­tory pat­terns are ex­pected to in­crease with the loss of avail­abil­ity of wa­ter and food. Re­cent stud­ies have found that a num­ber of fac­tors, in­clud­ing cli­mate change, hu­man ac­tiv­ity, grow­ing hu­man pop­u­la­tion, change in land use pat­terns, in­fras­truc­tural de­vel­op­ment, and re­cently, the pro­fu­sion of in­va­sive alien plant species are caus­ing wide­spread dis­rup­tion in mi­gra­tory pat­terns.

Ze­bras al­ready face ob­sta­cles in mi­gra-

tion routes. A study by Ger­man re­searchers in Botswana, pub­lished in the Pro­ceed­ings of the Royal So­ci­ety B re­cently, found that ze­bras rely on mem­ory to fol­low mi­gra­tion routes to reach fresh veg­e­ta­tion. “This mem­ory risks mak­ing in­ac­cu­rate pre­dic­tions of veg­e­ta­tion and wa­ter abun­dance as sea­sons are chang­ing,” Chloe Bracis of the Senck­en­berg Bio­di­ver­sity and Cli­mate Re­search Cen­tre, Frankfurt, told Down To Earth. “Mi­gra­tion routes of ze­bras are threat­ened by cli­mate change and land use changes in south­ern Africa,” says Bracis.

How­ever, Sam Weru, a wildlife and con­ser­va­tion con­sul­tant based in Nairobi, be­lieves an­i­mals com­bine both in­sti­tu­tional mem­ory and an “in­nate” ca­pac­ity to de­tect and read en­vi­ron­men­tal con­di­tions to guide their mi­gra­tion. He cites the ex­am­ple of the wilde­beest, which is known to de­lay birth when rains are de­layed. Ze­bras, he says, are more likely to mi­grate fol­low­ing the eco­log­i­cal in­flu­ence of other species like wilde­beest through the process of “Eco­log­i­cal Fa­cil­i­ta­tion”, where the feed­ing be­hav­iour of one species in­flu­ences or fa­cil­i­tates the ac­cess to for­age ma­te­rial for an­other.

Bernard Ag­wanda, a mam­mal spe­cial­ist with the Na­tional Mu­se­ums of Kenya, says ze­bras have been known to tra­di­tion­ally reach food and wa­ter us­ing the same path all the time, due to what is called “evo­lu­tion­ary im­pris­on­ment” in their genes, a be­hav­iour that helps them avoid risks such as be­ing at­tacked by preda­tors.

Among the re­cently stud­ied risks to the dis­rup­tion of mi­gra­tion pat­terns is the un­prece­dented growth of in­va­sive alien plant species in the Maa­sai Mara-Serengeti re­gion. A study by the Cen­tre for Agriculture and Bio­sciences In­ter­na­tional (cabi), the UK, the Kenya Wildlife Ser­vices, Nairobi, and South Africa’s Stel­len­bosch Univer­sity, pub­lished on May 22 this year in Koe­doe, found that as many as 160 alien plant species have taken roots in the Maa­sai MaraSerengeti ecosys­tem.

Of th­ese, 23 were found to be in­va­sive, spread­ing ag­gres­sively and threat­en­ing to colonise in­dige­nous bio­di­ver­sity. “We pre­dict that in the ab­sence of ef­forts to con­tain, or re­verse the spread of in­va­sive alien plants, the con­di­tion of ran­ge­lands will de­te­ri­o­rate, with se­vere neg­a­tive im­pacts on mi­grat­ing large mam­mals, es­pe­cially wilde­beest, ze­bra and gazelles,” the study found.

Some of the in­va­sive plant species in­clude the famine weed (Parthe­nium hys­teropho­rus), mesquite (P juliflora), devil weed (Chro­mo­laena odor­ata), lan­tana or tick­berry (Lan­tana ca­mara), cac­tus (Opun­tia sp) and the Mex­i­can sun­flower (Titho­nia di­ver­si­fo­lia). The re­searchers found th­ese species in the fields next to the Maa­sai Mara game re­serve, and say they could spread through­out the wildlife re­serve very soon.

In­va­sive plants dis­place na­tive species and deny an­i­mals their feed. “Most in­va­sive plants are toxic and un­palat­able. They are not eaten by live­stock or wildlife and they are also ag­gres­sive in dis­plac­ing na­tive species. In other words, they are re­duc­ing the amount of for­age avail­able, while some also form dense thick­ets prevent­ing the move­ment of wildlife,” Arne Witt of cabi told Down To Earth.

Ex­perts say that her­bi­vores such as wilde­beest, ze­bra and gazelles will be the most af­fected, and this will have knock-on im­pacts on other wildlife, in­clud­ing many preda­tors. In­va­sive plants will “al­ter the whole ecosys­tem as we know it.” Witt says cli­mate change can fa­cil­i­tate plant in­va­sions due to in­creased dis­tur­bances re­sult­ing from droughts, floods and other ex­treme weather events, adding that some in­va­sive plant species may ben­e­fit from in­creased car­bon diox­ide lev­els in the at­mos­phere. “In­creased in­fras­truc­ture de­vel­op­ment such as the con­struc­tion of roads and ho­tels as well as the pro­lif­er­a­tion of tourist jeep trucks may fa­cil­i­tate plant in­va­sions,” Witt ob­serves.

Among the big­gest threats to mi­gra­tion pat­terns are in­fras­truc­tural de­vel­op­ment, hu­man set­tle­ments, agriculture and pas­toral­ism. When pas­toral com­mu­ni­ties liv­ing close to wildlife re­serves graze their an­i­mals next to parks, their live­stock com­pete for pas­tures with wildlife, mak­ing wild an­i­mals miss out on for­age in times of mi­gra­tion. On the other hand, in­va­sive species are of no value to her­bi­vores and even in­sects, mak­ing move­ment and graz­ing im­pos­si­ble due to use­less veg­e­ta­tion.

There are some ways to buck th­ese dis­turb­ing trends. To mon­i­tor mam­mal pop­u­la­tions, re­searchers de­vel­oped Wild-ID, an un­usual wildlife photo-iden­ti­fi­ca­tion track­ing method. Us­ing this tech­nol­ogy, re­searchers have seen that as the num­ber of mi­gra­tion routes goes down in the Tan­za­nian ecosys­tem, so does the pop­u­la­tion of the wilde­beest. This find­ing was pub­lished in Bi­o­log­i­cal Con­ser­va­tion in 2016. Stud­ies have shown that Wild-ID is more ac­cu­rate, less in­va­sive, less ex­pen­sive, less time con­sum­ing and cov­ers more ter­ri­tory than tra­di­tional mark re­cap­ture and ae­rial sur­vey meth­ods. As for in­va­sive alien species, ex­perts rec­om­mend re­mov­ing species which are in­va­sive and the in­tro­duc­tion of con­trol pro­grammes to con­tain their spread.

Apart from agriculture, pas­toral­ism and in­fras­truc­tural de­vel­op­ment, more than 160 alien plant species are threat­en­ing the mi­gra­tory path­ways

THINKSTOCK PHOTO

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