Causes and Consequences of the Impact on the Ecosystem

The decline of large mammals in an environment can cause lasting effects on the ecosystem both economically and culturally. This decline, for instance, can result in lower animal protein supplies to local human populations, a decline in tourism, as well as long-term effects on vegetation structure. Several mammal populations have been declining over the recent years throughout southern Africa due to habitat loss from the exploitation of land for business use and from the exploitation of animals for food or game.

Little research has been conducted on the large decline in herbivore population impacts on mutualistic relationships. However, it can be seen that the large mammal population declines have been resulting in an adverse effect on oxpecker populations declines.

To begin with, authors Nathan Diplock and Kate Johnston, along with other researchers, observed the large mammal community along with the quantities, host preferences, and behaviors of red-billed oxpeckers and yellow-billed oxpeckers in Tanzania. Diplock and Johnston used a space-for-time observational approach to conclude their ults regarding oxpeckers and their preferred feeding habits.

Oxpecker populations were found less in highly hum human-populated as due to the scarcity of large mammals. Diplock and Johnston found three striking behaviors of the two different oxpeckers, (1) oxpeckers were feeding on larger host species within the mammal community, (2) oxpeckers preferred feeding on larger mammals, and (3) oxpeckers preferred hosts that were tolerant of their presence. There is a positive correlation between host species masses and the presence of red-billed oxpeckers and yellow-billed oxpeckers. Researchers found that cattle were very tolerant of the oxpeckers and their presence due to their larger size.

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Additional research was done to conclude the types of ways the oxpeckers extracted ticks, with Diplock stating:

Resting and scissoring compromised more than 80% of observed RBO behaviors when associated with buffalo, cattle, giraffes, and impala hosts. When associated withgiraffese, patterns of YBO behavior and attachment locations were similar to those of the RBO. In addition, restingconstitutedd 40-70% of YBO behavior across buffalo, cattle, and giraffes (7).

Scissoring is the technique used by oxpeckers and other birds of sweeping the host’s body while opening and closing the bill. Little research was found that oxpeckers were parasitic other than feeding on a giraffe’s wound which Diplock addresses by stating, “there is some evidence that RBO and YBO feeding may prolong wound healing, in addition to removing blood and other tissue from associated hosts” (2). Overall, it is rather weak evidence for scientific researchers to conclude that oxpeckers are parasitic. Instead, Diplock and Johnston conclude oxpeckers to be mutualistic with larger mammals with a rare exception to have a parasitic relationship with giraffes.

Moreover, with Diplock and Johnston summarizing the behaviors of red-billed and yellow-billed oxpeckers, author Kalle goes in-depth on how mutualistic relationships are being affected by changes in biotic interactions as well as the environment. These mutualistic relationships are impacted directly by human actions such as cutting down forests where oxpeckers inhabit, the use of poisonous acaricides, as well as dumping chemicals into water bodies that oxpeckers occupy. The red-billed oxpeckers and the yellow-billed oxpeckers are the only symbiotic mammal gleaners located in Africa with their preference being for larger host animals. Both oxpeckers emit antipredator warning calls and feed on large mammals to reduce the tick load. Due to the declining oxpecker populations in Africa, there are substantial efforts in place in South Africa to assist in population recovery of the oxpecker population. Conservation programs have been put in place to encourage landowners of South Africa to cut down on acaricides because these are killing the ticks and leaving the oxpeckers without food. Other conservation programs plan to set up oxpecker habitats in the savannas, water bodies, and woodlands. Acaricides are the major factor influencing the decline in both red-billed and yellow-billed oxpeckers in South Africa even though they have been known to reduce the ectoparasites on the mammals. With the conservation programs that are being put in place, it would ultimately help the population of oxpeckers to recover to continue the effort to grow the mutualistic relationships of oxpeckers to larger mammals.

In addition to Kalle’s research on acaracide effects on oxpecker populations, researcher Kalle furthermore summarized key habitats of oxpeckers being in woodland, thicket, savanna biome, and water bodies. Kalle also summarized that the oxpecker population was substantially higher in areas with tree cover and in areas with high rainfall (9). This leads researchers to conclude that seasonality and climatic conditions impact tick development. Ultimately, lack of tick development results in a negative effect on oxpeckers because they feed on both larvae and adult ticks but if there are no ticks due to a colder climate, the oxpeckers in that area with the climate will reduce. This impact on tick development thus reduces the oxpecker population because their availability of food is in decline.

Furthermore, to bridge onto the effects of acaricides and the oxpecker population, author Keesing and her research group observed the effects of ticks and the effects of acaricide on cattle for long-term over seven years. Two species of ticks, Rhipicephalus pulchellus and Rhipicephalus praetextatus were found in the population’s habitat on the large mammals. It was found by Felicia Keesing that the density of ticks increased based on the amount of rainfall, asserting, “In 72 months of surveys spanning 1999–2006, we sampled over 500 km of savanna transect, collecting over 40,000 ticks. Annual rainfall during this period varied from a low of 344 mm in 2000 to a high of 839 mm in 2004” (4). Keesing concluded that the majority of the ticks survey was Rhipicephalus pulchellus. In addition to observing tick density, Keesing also observed how these areas handled acaricides produced by landowners to reduce ticks. Keesing noticed that the reduction of ticks in the African savannas resulted in health benefits for both humans and wildlife by declining parasitic relationships within the community. However, she also found these benefits must be weighed against costs to oxpeckers because it reduced their availability of food.

Consequently adding to tick reduction resulting in oxpecker reduction, Author Ndlovu conducted a research study on the feeding preferences of red-billed and yellow-billed oxpeckers in South Africa. Ndlovu and his group of researchers found that red-billed oxpeckers had a less diverse amount of hosts than yellow-billed oxpeckers. Oxpeckers serve as tick control on domestic and wild mammals by mutually getting fed and reducing several diseases in mammals, “By removing ectoparasites, Oxpeckers reduce host exposure to tick-borne diseases and the negative effects from ticks such as tick toxicosis, metabolic disturbances, anemia, and tick worry” (Ndlovu 1). Ndlovu also found that host feeding behaviors such as around the eyes, around the nose, around the mouth, and around the ears were fairly common among the two different groups of oxpeckers, Ndlovu explains:

A total of 419 body-location preference instances were recorded. Red-billed Oxpeckers were most frequently observed on the back (41%, n = 170), head (20%, n = 83) and neck (16%, n = 65). The neck was particularly preferred on Giraffe (40%, n = 25), whilst the flanks were also important for Kudu (19%, n = 7). Oxpeckers were also seen on the legs and anogenital regions of hosts (4).

According to the data, both red and yellow-billed oxpeckers displayed a preference for the head and the back of the host where most of the ticks would burrow. Ticks often burrowed on the head and back for warmth from the host. Only a small percentage of ticks were found on the flanks of mammals. And only a small amount of wound feeding by the oxpeckers was observed by Ndlovu’s research group. It was observed that the oxpecker population declined in this part of Africa during Ndlovu’s study due to tick reduction from pesticides. It was also determined and concluded that oxpeckers are significantly mutualistic animals for they are helping out their larger mammal host by reducing disease as well as helping themselves get fed.

All in all, it can be seen that red-billed oxpeckers and yellow-billed oxpeckers had a distinct type of habitat in which they fed off of ticks to help out their larger mammal counterpart. Oxpeckers were observed in areas with significant rainfall and warmer temperatures such as woodlands, water bodies, and savannahs. Oxpecker behaviors were recorded largely as feeding on bigger mammals with tolerance to their presence as well as feeding on specific areas of the back and head of the mammals where the ticks burrowed and gathered for warmth. Finally, oxpecker populations were also observed to decline from pesticide use on ticks which ultimately lessened the need for oxpeckers to feed on larger mammals.