The Life of Vultures

 

Turkey Vulture (Cathartes aura) soaring. The underside of the
 primary and secondary feathers of Turkey Vulture wings are silver. 
Palm Beach County, Florida.

Vultures get a bad rap.  Their dark feathers and naked heads are not very appealing.  Their diet of carrion may even be appalling.  In western cultures vultures are viewed as ill omens, representing death, but ancient Egyptians held and Hindus still hold vultures to be sacred.  Vultures have a fascinating biology with adaptations for eating dead animals. They are masters of soaring.  Vultures can catch thermals and ride to high altitudes with little expenditure of energy.  From these great heights they scan the earth for their next meal.  Sometimes large number of vultures can be seen soaring together.  A group of soaring vultures is called a kettle.  The collective noun for a group of feeding vultures is, appropriately, a wake. 

A kettle of Turkey Vultures rising on a thermal.

Horry County, South Carolina. 

Black Vulture (Coragyps atratus) in flight.
The feathers at the tips of the wings are silver.
Mecklenburg County, North Carolina.  

Two species of vultures live in eastern North America, the Turkey Vulture (Cathartes aura) and the Black Vulture (Coragyps atratus). Vultures are raptors related to hawks and eagles.  Like hawks and eagles, vultures have hooked beaks for tearing their food. Unlike hawks and eagles that have powerful toes and talons for capturing and killing prey, vultures have weak toes with blunt talons because their prey is already dead. Both species of eastern North American vulture lack feathers on their heads and necks.  The bare head makes it easier to keep clean after feeding inside a dead animal.  Both Black and Turkey Vultures have perforate nostrils.  When viewed from the side you can see through the nostril.  

Turkey Vulture showing its perforate nostril. This species
of vulture has a highly developed sense of smell. 
Horry County, South Carolina. 

Turkey Vultures are large birds, with a wingspan of about 6 feet.  At a distance, Turkey Vultures appear black, but closeup they are dark brown.  The flight feathers of the wings are sliver beneath and the contrast with the rest of the wing is striking.   Turkey Vultures soar with their wings held up in a shallow vee, a dihedral, and rarely flap.  Turkey Vultures have naked, red heads. This gives the Turkey Vulture its name because it resembles the head of the Wild Turkey (Meleagris gallopavo).  Unlike most birds, Turkey Vultures have a well-developed sense of smell.  They can detect a rotting animal by smell then zero in on their meal visually.  Natural gas pipeline companies use the Turkey Vulture’s sense of smell to help detect leaks in their lines.  Natural gas itself has no odor so the refiners add an odoriferous compound, ethyl-mercaptan, so the users of gas appliances can tell if there is a leak.  This chemical is also emitted by a rotting animal and a leak in a natural gas pipeline attracts Turkey Vultures.  A kettle of vultures above a pipeline can alert the gas company of a leak.

Turkey Vulture perched. Although Turkey Vultures
appear black in flight they are really dark brown. 
Palm Beach County, Florida. 

A pair of Turkey Vultures flying in formation. 
Vultures often congregate in large groups. 
Mecklenburg County, North Carolina. 

Black Vultures are slightly smaller than Turkey Vultures with shorter wings and tails.  Black Vultures have less surface area for soaring, so they must flap more often than Turkey Vultures to stay aloft.  Black Vultures have black feathers and bare black heads.  They also have a patch of silver feathers near the end of their wings so are easy to distinguish from Turkey Vultures in flight. Black Vultures do not have the finely developed sense of smell of Turkey Vultures but what Black Vultures lack in sense of smell they make up for in aggressiveness.  Black Vultures often follow Turkey Vultures and displace them on a dead animal.  

Black Vulture in flight. 
Palm Beach County, Florida.

Black Vulture on the ground. 
Marion County, Florida. 

Vultures play an essential role in ecosystems.  They quickly dispose of carcasses and prevent the spread of disease. They can safely eat dead and even diseased animals because their digestive systems inactivate pathogenic microorganisms. Vultures quickly recycle nutrients in the environment and reduce greenhouse emissions.  A study of Turkey and Black Vultures in central Florida showed they can completely skeletonize a pig carcass in eight hours. 

Black Vultures feeding on carrion.
Rowan County, North Carolina. 

While American vultures are experiencing a population increase, the vulture populations in India are crashing.  The number of Indian vultures has decreased by 90% in the last 40 years.  This population decline was caused by the use of an anti-inflammatory drug as a veterinary treatment for domestic animals.  While this medicine was beneficial to the domestic animals, it was lethal to vultures that would scavenge the treated animals. The decline in vulture population has caused social disruptions too.  The Parsis are a distinct ethnic group in India and they practice Zoroastrianism, a religion that originated in ancient Persia.  The traditional funeral practice of Indian Parsis is to place their dead on stone towers, the Towers of Silence, where vultures consume the deceased.  With the decline in vulture numbers the Parsis have modified the Towers of Silence to include solar concentrators to heat the remains and dry them as they are eaten by smaller scavengers like crows and kites.  While vultures could remove the flesh from a body in a day, the process now may take weeks.  Another side effect of the loss of vultures in India is an increase in other scavengers like feral dogs and rats.  These animals can transmit rabies and plague and are a public health hazard.  

A Black Vulture warily watching a group of humans.
Mecklenburg County, North Carolina. 

Despite their distasteful habits, vultures are interesting creatures that provide essential ecosystem services.  They are large birds and they are magnificent flyers that can inspire the viewer, at least from a distance.