Grey-headed Gull tracking

Bird strikes with aircraft cost the international aviation industry millions of dollars per annum as a result of direct damage to aircraft and indirectly due to delays caused by aircraft down time.

O.R. Tambo International Airport (ORTIA) has a world class wildlife hazard mitigation program in place with six permanent staff using a range of methods to address the risks posed by birds on the airfield. The programme is highly effective in addressing bird presence on the airfield. Hazardous bird species often occur in large numbers in areas immediately adjacent to the aerodrome and either fly over the airfield passing through aircraft approach and departure paths or they come to the airfield to feed. Grey-headed Gulls (Chroicocephalus cirrocephalus) are a typical example of a species that occur in large numbers on the pans and shallow wetland areas or open fields around the ORTIA, Johannesburg, South Africa. The wildlife department at the airport maintains a detailed database of bird strikes as well as bird presence and abundance on the airfield. Data from the past 17 years indicate that Grey-headed Gulls rank as a high-risk species at the airport. Given that the gulls often congregate in large colonies near the periphery of the airport and from there venture onto the airfield, it is particularly difficult to mitigate the risks they pose as potential bird strike victims.

In order to develop an effective mitigation strategy to reduce the risk of collisions between the high density Grey-headed Gulls and aircraft at ORTIA, BirdLife South Africa and its collaborators are working together to fill the current knowledge-gaps about the daily and seasonal movements of the Grey-headed Gulls which live close to the airport. The gulls are typically present in larger numbers during the autumn and winter season. It is suspected that the birds forage in a wide area around the airport at landfill sites, shopping malls and various other sites such as compost facilities. Large scale breeding seems to also not take place every year near the airport but the aviation safety risk is significantly elevated when gulls breed in their thousands next to the airport. Gull presence and abundance is much lower during the warmer summer months.

Little is known and understood of the movement patterns of the gulls. The purpose of this project will be to establish in more detail the exact movement patterns of gulls over the eastern part of the Gauteng Province with the ultimate aim of using such information to better mitigate the risk these birds pose to aviation safety at ORTIA. Questions we hope to answer with the data collected through the monitoring will include:

• Daily movement patterns of the birds around the airfield
• Areas used / visited by the gulls other than the pans and open fields adjacent to the airport
• Identify potential alternate breeding sites used by the gulls in the eastern parts of the Gauteng Province
• Dispersal / movement patterns of the gulls during the summer season when their numbers and presence at the airport appear to be much lower

With such information, a better management / conservation strategy could be developed for the Grey-headed Gulls and areas could potentially be identified where breeding could be encouraged at localities where their presence and movement patterns would not pose a threat to aircraft landing and departing from the airport runways.

Trapping the birds

Many ideas were discussed regarding the most effective method for trapping Grey-headed Gulls near ORTIA. After some trial and error, mist nests (fine meshed nets placed between two poles) strategically placed around a lure (a dummy owl) worked out to be the easiest and most efficient way to attract and capture the Grey-headed Gulls. All birds were handled quietly and swiftly to ensure minimal stress. Once the harness and tracking device were attached, the birds were immediately released.

Data collection

The trackers connect to the online server through the GSM network once a day and data points are downloaded for analysis at the end of each month. The preliminary movements of the birds can be seen below.