Archive | September 2017

Dynamic Landscape of Fear

Lions with zebra kill

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The Snapshot team have written another paper using the Snapshot data we all help to classify. The paper A ‘dynamic’ landscape of fear: prey responses to spatiotemporal variations in predation risk across the lunar cycle can be found at http://onlinelibrary.wiley.com/doi/10.1111/ele.12832/full for those of you interested in reading the original.

Lead by Meredith Palmer the paper explores how four ungulate species, buffalo, gazelle, zebra and wildebeest respond to predation risk during differing stages of the lunar cycle. These four make up the bulk of the African lion’s diet in the Serengeti along with warthog. Of course warthog are strictly diurnal so are not affected by the lunar cycle as they are tucked up nice and snug in a burrow.

For the other four night time can be a stressful time. None of these animals sleep all night, they snatch rest here and there, keep grazing and most importantly of all keep a watchful eye or ear out for possible attack.

It has long been thought that prey species territory is shaped by fear and that animals have safe areas (where they rest, give birth, etc) and risky areas where they instinctively know predators may be lurking. These areas trigger a risk versus reward response as they often contain better forage/water etc.

What Meredith and the team argue is that this landscape of fear is very much dynamic changing not only with seasons and night and day but on a very much finer scale as influenced by light availability through the moon.

Lions find it so much easier to hunt during nights where the moon gives of least light. It gives them a great advantage to stalking close to their prey using the dark as a kind of camouflage. The prey species, on the other hand, are at a distinct disadvantage, they can’t see the stalker and even if they sense its presence they are reluctant to flee as this presents a great risk in itself if they can’t see.

Meredith and her colleagues took the data from Snapshot Serengeti to quantify nocturnal behaviour of the key species using the presence or absence of relaxed behaviour (defined when we classify a species as resting or eating.) They then overlapped this with data collected through Serengeti Lion Project on lion density and hunting success. This data enabled them to work out what areas where high or low risk to the prey species. Using a clever statistical program, R, the data was analysed to see if lunar cycle had any bearing on animal behaviour, in particular, predator avoidance.

They found that moonlight significantly affected the behaviour of all four species but in a variety of ways. As we mentioned before there is often a good reason to venture into the high risk areas and the trade off in increased risk of predation is a really good feed. Buffalo for instance don’t change their use of space so much but were found to form more herds on dark nights. It seems safety in numbers works well for buffalo. Zebra react similarly in their herding activity but are much more erratic when it comes to space use, moving around a lot more randomly keeping potential predators on their toes.

Each species showed an aversion to using high risk areas at night but, particularly wildebeest and zebra, were found to increase their use of these areas when the moons luminosity was higher and safety increased. It was noted that high risk areas where avoided more frequently in the wet season than the dry. The thought being that there is increased hours of moonlight during the dry season that the animals take advantage of. Perhaps too the drive to find enough good food is a factor.

This paper serves to remind us that although what we do at Snapshot Serengeti is fun it is more than just a way for us classifiers to pass the time. It really has a very significant role in science and that role is ever increasing.

 

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Meet The Dikdik, Master Of Cool

 

Male dikdik

 

The Serengeti plains hold a wealth of wildlife familiar to us all. As long as our camera trap images are clear most people have no problem identifying wildebeest, zebra, giraffe and impala. It is some of the smaller antelope that prove a bit of a problem. The smallest of the Serengeti’s antelope, the dikdik is not so well known but what it lacks in size it makes up for in a fascinating life history.

So what makes this diminutive antelope so special and how does it survive living in the lion’s den, so to speak.

It is the antithesis of the wildebeest. Instead of running as a herd of thousands the dikdik live fairly sedentary lives, instead of a constant male battle for mating rights to a harem of females the dikdik forms pair bonds that last for life. Essentially it opts for a quite life under the radar. Living in bushy scrub and kopjes gives it plenty of places to stay hidden and its ability to reach up to 42km/hour enable it to escape even the swiftest of predators. Though of course dikdik do end up on the menu sometimes.

Dik dik are territorial and use dung, urine and scent to mark the boundaries. The scent comes from preorbital glands on the face which is rubbed on sticks. All members of the family will contribute to these markers but it is the male that does most of the work. The strange twist is that males are subordinate to females in the pair bond so really the male is marking and defending his mate’s territory for her. I guess it pays to keep your missus’ happy when you pair for life.

Obviously whilst holding a territory you will have neighbours and that is certainly the case for dikdik pairs but it seems that the peace is kept by making sure you only add more dung/urine/scent to your side of the heap. Dikdik must have the most defined territory of any antelope in the Serengeti. If there is a border dispute it can lead to mass pooping; as many as 10 dung piles per 100 meters which is three times as many as a normal border.

Traditionally there were thought to be 4 species of dikdik mostly restricted to East Africa with one, Damara dikdik, found in Namibia. New work suggests that the four subspecies of Kirk’s dikdik are actually full species making Cavandish’s dikdik (madoqua cavandishi) the species we are familiar with from the Serengeti. It’s hard to keep up with systematics.

One of the most amazing adaptations in dikdik’s is their central cooling system which allows them to live in arid, hot conditions. To cool down they increase their breathing rate from 1 to 8 breaths per minute. This passes over numerous blood vessels in the flexible proboscis (that oversized long snout that makes dikdik look so odd) cooling the blood. From here the cooled blood passes back to the heart through the cavernous sinus. Due to the large surface area in the sinus as hot blood is pumped to the brain a form of heat exchange takes place allowing cool blood to be pumped to the brain ensuring that brain function is not impaired by hot conditions even if body temperature is elevated. This is a trait that dikdik share with other dessert adapted animals such as oryx and camels.

So small it may be but the dikdik is not to be dismissed without some appreciation for its ability to survive in pretty harsh conditions.