Are Oxpeckers More Like Vampires Or Vacuum Cleaners?What could be a better example of a win-win situation in the wild than an oxpecker busily removing ticks from the back of a buffalo? The oxpecker gets a square meal, a place to perch, fur for nesting and all sorts of other benefits, and the buffalo gets rid of a bunch of parasites that could potentially spread a life-threatening disease while removing the buffalo's blood, plus the added benefit of having a whole lot more eyes watching for predators and sounding the alarm when necessary. But look a little bit closer, as scientists are fond of doing, and the win-win situation starts looking a bit like the oxpeckers have a lot in common with the ticks - mainly their thirst for blood. Over the years, observers have noted that oxpeckers don't solely confine their activities to the search for ticks - some have the rather unpleasant habit of opening up any wounds they can find on their host and indulging in a blood meal without the benefit of their normal middleman, the tick.
Some have even reportedly tried to deliberately create wounds to get at fresh blood. Now Tiffany Brooke Plantan from the University of Miami in Florida, USA, is coming to the Kruger National Park (KNP) to look a bit more closely into the relationship between oxpeckers and their hosts in partial fulfilment of her doctoral degree. If the oxpecker and the buffalo (or any other animal the oxpecker finds a meal on) are both benefiting from their relationship, then biologists refer to it as a mutualistic symbiotic relationship, where both parties win out in the end. In comparison, the tick is not benefiting the buffalo overall - it just sits there and sucks up blood until bloated - and this is a parasitic relationship because only the tick benefits.
But if the oxpecker ignores its normal meal of ticks and spends more time opening up half-healed wounds and drinking the blood that wells up, making the wound take longer to heal and harming the host to an extent, then the oxpecker starts looking less like a symbiotic friend and more like a parasitic foe. But there seem to be shades of grey between the different kinds of symbiotic relationships that exist, a situation termed conditionality. In conditionality, the interaction between the species varies along a continuum from parasitism (winlose) to commensalism (one wins, one stays even with no benefit or loss) to mutualism (win-win), depending on the context in which the interaction takes place and the players involved. Is it possible that sometimes oxpeckers are friend and sometimes they are foe? What drives the herbivore and the bloodthirsty bird to co-exist? And does the relationship depend on how many ticks are available for the birds to eat, or what type of ticks they are, or do the oxpeckers really just prefer fresh blood but are only tolerated if they also do tick removal?
To answer these questions, beginning in January next year, Tiffany will spend six months in Kruger in the Punda Maria/ Shingwedzi area intensively watching the interactions between oxpeckers and their hosts, recording what the birds get up to when they feed and how this changes with the seasons. Tiffany says that the oxpecker-host relationship "is distinct in that it has been studied beginning as far back as the early 20th century, yet many unanswered questions remain." As well as the field observations, Tiffany will rope some donkeys into her research, and make use of the research centre at the Pretoria National Zoological Gardens. Oxpeckers are known to feed off 20 different species of wild animals, and about six domestic ones, with the two most popular tame animals being cattle and donkeys. Obviously, a researcher cannot wander up to a buffalo or a giraffe and count the number of ticks and wounds that it has before an oxpecker lands on it, but a research donkey can be planted with a set number of ticks and have its wounds counted before an oxpecker is released under controlled conditions to find its breakfast on the donkey.
This set-up will allow Tiffany the chance to see whether the oxpeckers head straight for the ticks or spend more time pecking at the wounds on the donkey. She will also be able to tell whether the donkey is tolerating the attentions of the oxpecker, or regards it as more of a nuisance. Oxpeckers have a hearty appetite, with an adult red-billed oxpecker being known to consume approximately 100 adult female blue ticks in a day, or 12,500 of the smaller nymphs. In order to obtain ticks to feed the oxpeckers, Tiffany will have to collect them from the veld - potentially ticks of at least four different species that the oxpeckers are known to prefer.
She will use two methods, both of which rely on the fact that ticks sit on grass stalks waiting to hitch a ride on an animal host. The first method involves dragging a soft white flannel cloth over the grass and removing ticks that become attached to the cloth with forceps. Ticks that are collected for monitoring purposes and not for feeding will be preserved in ethanol to later be identified in the lab. The second method involves going into a specific plot of the bush and plucking the adult ticks off the grass by hand. Enough ticks have to be collected to let Tiffany infest the donkeys to the point that the oxpeckers have an oversupply, to check whether they would really rather head for a wound even if given an excess of tasty ticks. Tiffany comments, "It will be a very challenging and meticulous task to make sure I have all the ticks ...not only the species, but also the stage and sex. It is likely that I will have a 'tick breeding experiment' within my oxpecker feeding trial experiment!" The tick collection will also be carried out monthly in a set area of Kruger for an entire year to check how the abundance of ticks in the veld changes between the wet and dry seasons, to see if this ties in with oxpecker behaviours. Tiffany will also do feeding trials with captive birds to see what they choose from a food array on small dishes, offering the options of different species of engorged ticks, ticks that are not full of blood, blood and minced meat all at the same time, to see what individual birds prefer.
The feeding trial will also involve discovering the calorie content (like that reported on a box of cereal or a bar of chocolate) of the various food offerings By the end of next year, Tiffany will hopefully be several steps closer to knowing what both yellow-and red-billed oxpeckers like to eat, but will also have gathered more scientific information on the relationship between the birds and their hosts - and whether it is always win-win with the oxpecker and the buffalo, or if just maybe the oxpeckers are putting one over on the buffalo - the bird might be mightier than the bull...
By Melissa Wray
In Kruger National Park