A 'plague' of rats in Amboseli

Mon, 2007-06-25 04:13 by hcroze · Forum/category:

If it's not one thing, it's another.

The ecosystem constantly has its knocks: too little rain, elephants getting speared, too many permanent settlements crowding the park boundary ... This dry season it's also rats!

Unstriped grass rat, Arvicanthis spp.
Unstriped grass rat, Arvicanthis spp.

For the past two months, elephant researchers working staying at ERC (Elephant Research Camp) have noticed increasing numbers of small, brownish rats scurrying in and out of the long grass onto the mowed pathways between the tents.

They were skittish at first but are now nearly as confiding as the camp's birdlife and zebras. At any one time there may be a dozen grazing busily within twenty feet of the researchers' breakfast table. They scuttle into the long grass at the base of the palms as you walk by, and reemerge a few seconds later in your wake barely missing a bite.

Jonathan Kingdon's Field Guide to African Mammals confirms that our little visitors are one of the several species of the genus Arvicanthis, with the unglamorous English name, 'Unstriped grass rats'. They are diurnal grass-eaters. Kingdon, in his encyclopaedic East African Mammals: an Atlas of Evolution reckons that they are most active in the early afternoon, during the 'siesta' lull in avian and mammalian predator activity. 'Our' rats are probably benefiting from their proximity to humans that keeps predators away, since they seem to be busy all day.

Two rats greeting
Two rats greeting

Although Kingdon reports that several litters may be born during the wet season, 'our' rats have a number of young, probably only a few weeks old, likely to have been conceived during the earlier part of this dry period that looks like it will be a long, bad one. The heavy rains last November and December (60% of the average annual total) probably charged the water table sufficiently to keep the grass supply robust in Ol Tukai Orok (the area around ERC) till today.

One of the adult males has a conspicuous white blaze on his back. We call him 'White Fang'; he seems to be dominant to the others.

White Fang disciplines subordinate
White Fang disciplines subordinate

The Arvicanthis are doing well, eating like mad: we can almost discern their grazing impact along our pathways. One of our Maasai staff, Saruni, tells us that his people are very unhappy about the toll the hoards of little grazers are having on the dry-season diminishing grasslands outside the park: they are competing successfully with the cattle!

At least they can't blame the elephants for this one!

Rats at the camp

Fri, 2007-06-29 00:04 by Jan

For those of you staying at the camp, my concern would not be the rats but the extra snakes that might be attracted to the rats! Please all be careful.

Thanks, Jan, that occurred

Fri, 2007-06-29 07:03 by hcroze

Thanks, Jan, that occurred to us, too. We always keep a weather eye out for snakes (although they are rarely seen) and we zip up tents tightly when not arround to keep out both them and the pesky Vervet monkeys. Cynthia does have a Black Mamba more than 10 feet long who lives in the vicinity of her tent. Suspect it is delighted with the outbreak.

HC

rats and plague

Mon, 2007-06-25 09:34 by Keith

Hmm, the last time I recall a deluge of rodents was in 78/79, when there was big rain following the dry years of '74-76/77. The grass rose up and the rats came in right after. Could this population boom be due to the big rains of earlier in the Amboseli Year? One of the consequences of the rat boom was that people started getting lots of flea bites and coming down with a mystery disease, with big black boils and some fairly serious sickness, though not a great lot of actual mortality, I seem to remember. The diagnosis was Bubonic Plague !!! But apparently not of the Black Death, Bring Out Your Dead variety. It could be treated fairly readily with antibiotics if caught early enough. However, there was a certain amount of mild panic and health officials bucketing around Ilkisongo.

Has anyone been in touch with local health authorities to ask them if a repeat of the Plague is likely? Could we sound an early warning, or would it just be a false alarm? Might be worth a word or two with someone...

Some links on the subject....

Wed, 2007-06-27 05:56 by hcroze

Googling on 'avrvicanthis plague' turned up a number of sites. http://canarydatabase.org/browse/species/1022641, an interesting site that deals with 'Animals as Sentinels of Human Environmental Health Hazards'. And http://www.ingentaconnect.com/content/bsc/jbiog/2004/00000031/00000002/a... reminds us that the hazard has been around since Pharaonic times.

Seems we are not alone in our concerns, although not clear if any local authorities taking action. Perhaps Soila can bring it to the attention of the District Commissioner.

HC

To quote Jonathan Kingdon

Mon, 2007-06-25 13:09 by hcroze

East African Mammals, Vol IIB, p. 629: "Arvicanthis have been reported to the carriers of the plague bacillus in the Congo, but Hopkins doubted the adequacy of these reports for this species. In a series of experiments Weinbren and Mason (1957) show that Arvicantis is able to circulate Rift Valley Fever virus without succumbing to the infection. They suggest that the species might be a natural host for this disease."

HC

Is there a vaccination for The Plague, or RVF?

Tue, 2007-06-26 15:27 by Keith

Who is Hopkins to doubt The Plague? I have no idea whether my memory is accurate, or if the medics changed their story after the dust settled back in '78/79. All I know is that Maasai houses were full of rats/mice (even nipping at toes in the night), that people were bitten by fleas (as was I during visits to settlements) and that there were cases of some disease or other all over the place. How could we verify this? Does anyone know an old doctor or public health type who was around at that time and is still around, with intact brain cells? I still think the possibility of a rat-borne disease outbreak should be mentioned to local officials...

Another thought: what animals eat Arvicanthis? Some of the smaller mammalian predators and/or birds of prey? There could be a "cascading" effect on other trophic levels: the grass we know about from the Maasai and HC's pers comm in the camp, but predators could also be affected. A short note to East African Nat Hist Soc, or a box in the Intro Chapter?

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