Vultures and Aeroplane Collisions

A very important aspect of the relationship between vultures and urban development concerns the collisions between these birds and aeroplanes, usually near airports in large cities (Lowney 1999; Avery and Cummings 2004; Blackwell and Wright 2006). Unlike road kills, where mostly mammals collide with road vehicles and vultures may eat the carcasses, in aeroplane collisions, the vultures are the animals killed. Vulture collisions occur largely in southern countries, due to the tropical and subtropical distribution of most vulture species. In northern countries, Larus gulls and other seabirds compete with raptors. The literature on vultures appears more scanty.

Vulture collisions with aeroplanes are globally common, creating problems in both urbanized airport areas and the airspace over other landcover (Satheesan and Satheesan 2000). These authors record that between 1955 and 1999 more than 33 aircrafts (27 military and other civil) were destroyed, and 21 lives were lost because of collisions in seven countries in Asia, Africa, Europe and North America. In some cases, collisions have occurred at extreme altitudes. For example, on 29 November 1973 a Ruppell's Griffon collided with a commercial aircraft at 37,000 feet (11,280 m) over Abidjan, Cote d'Ivoire (Laybourne 1974). Curiously, the vulture in this incident was flying at an altitude where temperatures are about -50°C and oxygen is very thin.

Many accidents have been recorded in the United States, Spain, India, Pakistan, Kenya, Ethiopia and Tanzania and other countries. In the United States of America, aerpolane collisions with Black vultures cost more than US$25 million to the US Air Force (USAF 2009). Turkey vultures have also caused a lot of damage (Satheesan and Satheesan 2000). Also in Brazil, aircraft strikes are considered the most important vulture-related problem. The Aeronautical Accidents Investigation and Prevention Center (CENIPA) recorded more than 980 strikes involving vultures between 2000 and 2011. In Manaus, a total of 65 vulture-aircraft strikes were recorded between 2000 and 2012 (CENIPA 2012). In India, the losses were about $70 million annually from 1980 to 1994 due to vulture strikes (Satheesan 1994, 1996, 1998, 1999a). In India, all the crashes involved one species, the White-backed vulture; other species also had more minor encounters (Indian vulture, Slenderbilled vulture and Egyptian vulture). The African White-backed vulture, the White-headed vulture and the Ruppell's griffon brought down aeroplanes in Kenya. In other nations, such as the USA and Spain losses totalled about $10 million to $17 million per accident (Satheesan and Satheesan 2000).

The principal reasons for vulture collisions are solitary and communal thermal soaring, gliding between thermals, large bird size and slow reflexes on the part of the birds. Generalizing, most collisions occur when the plane is cruising, and a few during descent, where the altitude of the accident was known, about half were below 200 m; fighter jets are more likely than transport aircraft to collide with vultures, due to the high speed of the fighter aircraft at low latitudes.

One study examined mid-air collisions between Black and Turkey vultures and military and civilian aircraft at the Savannah River Site (SRS) in South Carolina, USA (DeVault et al. 2010). It examined the hypothesis that vulture flight characteristics were predictable with respect to weather and time variables. The results showed that Black vultures flew at an average altitude of 169 ± 115 (SD) m, whereas Turkey vultures flew at an average altitude of 163 ± 92 m. These findings contrasted with other studies that recorded less frequent and lower altitude flights. The flight behavior of both species was only minimally influenced by weather and time variables. Food availability, inter- and intra-specific interactions, and physiological demands were more important. It was concluded that bird avoidance strategies should focus on the variable flight behaviors of Black and Turkey vultures across their ranges (i.e., factors contributing to differences in flight behavior among regions), rather than examinations of the effects of local conditions on flight behavior.

Several methods have been devised to reduce bird-aeroplane collisions. Satheesan and Satheesan (2000), citing India, suggest the removal of vulture food sources within 100 km of civil airports and 200 km of military airfields, bombing ranges or low-level high-speed exercise zones. In practice, shooting birds is more common globally. For example, from 1991 and 1997 two to five hired shooters at JFK International Airport USA killed 52,235 gulls (47,601 Laughing Gulls, 4,634 others) in 6369 person-hours of shooting (Dolbeer 1998). Such shooting has also been practised in India. Satheesan and Satheesan (2000) point out that such shooting, which may create a vacuum into which other birds may enter to fill, and also be shot, is a factor for the low populations of vultures and other avian scavengers near aerodromes in India. Another problem is the low sanitation near airports, that encourage scavengers and might lead to the replacement of birds depleted through shooting (Blokpoel 1976; Ali and Grubh 1984; Satheesan 1992a, 1992d, 1994, 1996).