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Vulture Populations are Crashing

White-backed Vultures on an elephant carcass, Moremi Game Reserve, Botswana

White-backed Vultures on an elephant carcass, Moremi Game Reserve, Botswana

Vultures may have a bad reputation as scavengers with a disgusting lifestyle but they perform vital functions in the ecosystems across Africa.  And they are facing serious threats.  Populations of seven species have fallen 80% in the past three generations, mainly due to poisoning of carcasses.  This is unfortunate as vultures clean up carcasses and in doing so prevent the spread of disease and help recycle nutrients.  Besides, they are simply fascinating birds.

Cape buffalo reduced to bones by vultures and other scavengers

Cape buffalo reduced to bones by vultures and other scavengers

Most of the vulture species in Africa specialize in scavenging (though the Palm-nut Vulture eats fruit and the Bearded Vulture eat bones) and they have various adaptations for this gruesome niche.  They have excellent eyesight to find food and use thermals of rising hot air that allow them to soar for long distances while expending little or no energy (Lappet-faced Vultures can fly up to 800 km per day).  The wings are broad with "fingertips" (or slotting) at the wingtips to help reduce drag.  Their heads and necks are bare which may help in keeping themselves clean (or as some believe, help in thermoregulation).   Actually, vultures are clean birds.  After feeding they bathe in a nearby river or pan to wash all their feathers.  There is a hierarchy, based on body and bill size, among the various species when feeding at a carcass.  The largest vultures arrive first and with their heavy bills can rip out large chunks of meat.  The smaller species, like the Egyptian Vulture, typically eat last.  The White-backed and Cape Vultures have specialized spines on their tongues.  During a feeding frenzy they can quickly lap up soft material that isn't easily taken with the bill.

Their digestive tracts are highly corrosive allowing them to ingest putrid meat full of bacteria and kill the spores of disease causing microbes.  They can detoxify bacterial toxins that would kill other vertebrates.  Vultures reduce the number of mammalian scavengers at a kill so the transmission of diseases between infected mammals may be greater without vultures.  In the 1990's Asian countries experienced a >96% reduction in vulture populations and a parallel increase in feral dog numbers and rabies transmission.

a roost of white-backed vultures

a roost of white-backed vultures

Given the importance of the ecological role vultures play it's disturbing to read recent reports documenting the dramatic decline of vulture populations across Africa.  A June 2015 paper in Conservation Letters claims vulture are crashing to extinction.  The situation is particularly alarming for the rare White-headed Vulture (Trigonoceps occipitalis) which is declining 6.7% a year on average.  Three other species, including southern Africa’s largest vulture, the Lappet-faced vulture (Torgos tracheliotos), are declining between 5% and 6% a year.

There are a number of factors contributing to the rapid decline of vulture populations.  The analysis done in the Conservation Letters paper estimates 61% of vulture fatalities are from poisoning of animal carcasses.  Farmers living near national parks treat cattle carcasses with toxic agricultural pesticides to target lions and hyenas that kill their livestock.  Vultures are accidental victims.

Poachers that shoot elephants and rhinos will poison the carcasses to directly target vultures.  Vultures circling above a kill can alert authorities to presence of poachers.  In 2013 about 700 vultures died from a poisoned elephant carcass in the Caprivi Strip of Namibia.

The illegal trade in vulture body parts accounts for about 21% of vulture deaths. Vulture body parts have long been important in African cultures where it is believed that they cure a range of physical and mental illnesses, improve success in gambling and business ventures, or increase intelligence in children.  Practitioners of traditional medicine will poison vultures and collect only their head or feet.

Vultures often die of electrocution from power lines and wind turbines.  A number of other factors are contributing to the demise of vultures including habitat loss, disturbance at nest site, and a reduction of large mammal populations.

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