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High Frequency of American Kestrel Strikes at the Montreal–Trudeau International Airport: A Case Study

Wildlife collisions with aircraft cause considerable damage to aircraft annually. An estimate for the associated costs of wildlife strikes to United States civil aviation is over $628 million USD annually (Dolbeer and Wright 2008). Among avian groups, the raptors rank as the third most frequently struck by aircraft in the United States, following gulls and pigeons/doves (Dolbeer and Wright 2008). This may be related to the habitats characteristic of airports and airports’ close association with water and large expanses of grasslands (Dolbeer et al. 2000, Merriman et al. 2007). These characteristics can fulfill the habitat requirements of a number of raptor species by providing them with sufficient source of food (e.g., small mammals, birds, and insects), as well as nesting and breeding sites (Baker and Brooks 1981, Dolbeer et al. 2000). In the United States, the American Kestrel (Falco sparverius) ranked tenth of all wildlife species that caused major damage to aircraft (Dolbeer et al. 2000). Since 1990, there have been 4545 reported raptor strikes in the U.S., and American Kestrels represented 33.7% of those strikes (Dolbeer and Wright 2008). Of kestrel strikes, 16 caused damage to an aircraft, representing a total of $1 268 813 USD (Dolbeer and Wright 2008). From 1997 to 2009, Montreal’s Pierre Elliott Trudeau International Airport (YUL) has been recording comprehensive data on wildlife strikes that occur within its airspace. The airport is located on the island of Montreal, Quebec, Canada. The vast open expanse of land (1800 ha) includes two parallel runways and a third cross-runway. The two parallel runways are bordered by open grassland, with drainage ditches to facilitate waterrunoff. Many species of animals have been recorded within the airport territory, including over 78 species of birds and 11 species of mammals. Data on kestrel strikes have been collected since 1997 by airport staff and contractors charged with wildlife control on the site. Bird strikes were reported by pilots, aircraftmaintenance personnel, and other airport employees, including wildlife-control personnel, firefighters, and maintenance staff. American Kestrels were the species most often struck by aircraft at YUL. The number of kestrel strikes increased significantly from 1997 to 2007 at (N 5 11 yr, r2 5 0.41, P 5 0.033; linear regression analysis using STATISTICA [version 8.0, StatSoft, Inc.]). Kestrel strikes peaked in 2008 with 21 strikes followed by 2007 with 13 strikes, 12 strikes in 2006 and 9 strikes in 2005. The timing of collisions, examined at an hourly scale, showed a bimodal pattern, with a primary peak in the morning to early afternoon (900–1300 H), followed by a secondary peak in the late afternoon to early evening (1600–1900 H). By monthly intervals, we found a peak in kestrel strikes during the summer months, particularly July and August. The season with the most strikes (summer) was also the period of fledging and post-fledging (Smallwood and Bird 2002). Approximately 2–3 wk post-fledging, young kestrels form small groups of nonrelated juveniles (Cade 1955, Lett and Bird 1987). Such groups have been observed at YUL, with up to nine kestrels foraging simultaneously in the same vicinity. Typically, groups of 4–5 kestrels forage together (H. Garland unpubl. data). Kestrels were often observed perch-hunting from runway approach lights and traffic signs. Kestrel breeding on airport property was confirmed in 2008 when two fledgling kestrels were found by airport personnel after they fell from a nest on an aircraft hangar (H. Garland unpubl. data). Preliminary analysis of stomach contents performed on approximately ten kestrels reportedly struck by aircraft and subsequently found dead on a runway indicated that the stomachs contained a large quantity of grasshoppers (Order Orthoptera). Wildlife-control staff at the airport observed that kestrels often landed on asphalt runways and taxiways to capture exposed grasshoppers (H. Garland and M.-A. Fortin unpubl. data). One effective way to minimize these aircraft strikes is to modify the habitat so it is less attractive to wildlife (e.g., by minimizing food, shelter, water, and open space; Transport Canada 2002). Specifically, we recommend that all frequently used perches in problem areas be equipped with a perching deterrent such as NixaliteE (Nixalite of America Inc., East Moline, Illinois, U.S.A.) or Bird-B-GoneE porcupine wire (Bird-B-Gone Inc., Mission Viejo, California, U.S.A.). Potential nest sites should be identified by wildlifecontrol personnel, and all potential nest sites modified to reduce potential nesting activity. Holes in buildings that are attractive to kestrels for nesting should be blocked prior to