Conflicts betweenexpandinggoose populations and aviation safety

AbstractWe here review the collision risks posed by large bodied, flocking geese to aircraft, exacerbated by recent major increases in northern hemisphere goose populations and air traffic volume. Mitigation of goose strike risks requires knowledge of local goose movements, global goose population dynamics and ecology. Airports can minimise goose strikes by managing habitats within the airport property, applying deterrents to scare geese away and lethal control, but goose migration and movements at greater spatial scales present greater challenges. Habitat management outside of airports can locally reduce goose attractiveness of peripheral areas, but requires stakeholder involvement and coordination. Information on bird strike rates, individual goose movements and goose population dynamics is essential to understand how best to reduce the risk of goose strikes. Avian radar provides tactical information for mitigation measures and strategic data on local patterns of goose migration and habitat use. In the face of expanding air traffic, goose distributions and populations, these threats need to be integrated with other local, national and international stakeholder involvement to secure viable solutions to multiple conflicts.Keywords: Aircraft, Airport, Bird strike, Geese, Population increaseIntroductionCollisions between wildlife and aircraft (usually bird strikes) are increasing globally and present a disproportionate challenge around airports where aircraft are vulnerable during approach, landing and take off (Dolbeer 2011). Geese constitute a particular hazard because of their flocking nature, large body size and attraction to extensive open landscapes of short managed grassland at airports. Although specific statistics are difficult to obtain, ducks and geese have been shown to constitute 20% of bird strike aviation accidents (Thorpe 2016), with geese globally responsible for at least 957 known reported bird strikes between 1983 and 1998, or 63.8 per year (Allan et al. 1999), and during 1990 a total of 2015, or 84.0 per year, voluntarily reported strikes in the US alone (Dolbeer et al. 2014). Aircraft operators bear the brunt of the cost of damaging strikes, estimating to cost over US$ 1.2 thousand million annually throughout the world (Allan 2002). Single engine repairs may cost upwards of US$ 1 million without taking into account lost opportunity costs and service disruption from damage and downtime (Allan 2002). Beyond economic impacts, goose strikes present an extremely serious threat to human life when aircraft are damaged beyond their ability to sustain controlled flight. This has been demonstrated by events such as the crash landing of an United States Air Force E 3 Sentry at Elmendorf AFB in September 1995 that resulted in 24 fatalities and the forced landing of US Airways Flight 1549 in New York Hudson River in January 2009; both events were the result of engine ingestions of multiple Canada Geese Branta canadensis (Flight Safety Foundation 1996; Marra et 2009).Airport operators are responsible under national and international legislation for mitigating the risks of bird strikes involving geese, and have used a variety of tools to achieve this aim. This is becoming particularly important given the rapid increases in some goose populations (see below) and the average 5.8% annual increase in global air traffic passengers between 2005 and 2016 (Statista 2016). Not surprisingly, in response to such universally operational challenges, there has been considerable development of international approaches and policy on the issue of bird strikes (see review in Buurma 2006) culminating in the development of safety standards ratified by the world community under the International Civil Aviation Organisation (IBSC 2006). In this analysis, we review some of the methods used to reduce goose presence in the onsite vicinity of airports, including habitat management, disturbance and lethal control. Analysis of the US Federal Aviation Administration bird strike data showed bird strike rates below 152 above ground level have decreased since 1990, while those above that level have increased (Dolbeer 2011). The decrease in bird strikes below 152 may be the response to effective implementation of measures onsite at airports and may suggest that there are growing issues associated with areas outside the jurisdiction of airports, especially within the landscape immediately surrounding airport ownership (Dolbeer 2011; Martin et al. 2011). For this reason, we here consider mitigation measures for dealing with geese both onsite and in areas outside airport boundaries.The hazards presented to the aviation industry by geese are further exacerbated by rising goose populations in North America and Europe which elevate risks (see Fox and Madsen 1997; Dolbeer and Eschenfelder 2003; Fox and Leafloor 2017). It is therefore important to consider strategically how to manage geese beyond the local measures taken by airport operators and address the multiple problems posed by recent increases in goose abundance and range. As well as attempting to consider how best to tackle local problems posed by geese around airports, we also come with recommendations about how to establish long term local, national and international involvement with other stakeholders to find common solutions to broader conflicts with geese. In particular, we recommend finding mechanisms to facilitate collaboration on research, experiences and data sharing, and the importance of a biological understanding of the behaviour, migration, distribution, ecology and population dynamics of the goose species causing issues.Understanding the nature of the problemProblems associated with geese physically present onsite at an airport require very different solutions compared to those posed by geese traversing over the airspace of an airport. Long distance migrant geese passing through during a brief annual migration window present a different level of risk and require different solutions to geese moving through the same airspace daily commuting between night time roosts and daily feeding areas, even when both lie offsite. It is therefore evident that a biological understanding of the behaviour, migration, distribution, ecology and dynamics of the goose population(s) concerned is fundamental for developing recommended mechanisms and best practice for reducing bird strike risk.Migratory geese that breed in northern latitudes, but winter further south, pose a different set of challenges to local or resident birds that spend the greater balance of their annual cycle in one region for managers tasked with maintaining aviation safety. Migrant geese may pass through airspace infrequently, as they transit between breeding and wintering grounds; however, they may do so at altitudes where they are difficult to manage by ground personnel and in numbers that increase the likelihood of a damaging strike. In such circumstances, all that can be done is to observe movements and alert pilots to these via the Automatic Terminal Information Service (ATIS) and/or direct communication with Air Traffic Controllers. When wintering grounds are juxtaposed with an airport, migrant geese can represent a persistent and significant risk. In contrast, local or resident birds may commute regularly between different elements in the landscape around the airport and represent a year round hazard, but may be more predictable in their movements and more amenable to local management.Copenhagen Airport at Kastrup (Denmark) experiences both migrant geese and resident geese. An example of a genuine migrant species is the barnacle geese Branta leucopsis that breed in the Russian Arctic and the Baltic, and winter around North Sea coasts. This population has shown exponential increase in recent years and exceeded 1.2 million individuals in 2015 (Fox and Madsen 1997). These geese pass through once annually in either direction in spring and autumn. These migration patterns are relatively regular in time and space (although mediated by local weather) and are therefore somewhat predictable in occurrence. In the case of locally based geese, the migratory barnacle geese contrast with those of the same species that nest on the island of Saltholm under the eastern approach to Copenhagen Airport (Christensen et al. 2015a). The local breeding birds also winter around North Sea coasts, but unlike their long distance migratory counterparts, these geese remain in the vicinity of Copenhagen Airport throughout the summer (May Christensen et al. 2015a). Telemetry studies of 10 individual females caught on Saltholm showed that these geese remained on Saltholm throughout much of their residency period, when they rarely flew above 20 The few tagged individuals that did not stay on the island to moult went to Sweden, whereas the rest travelled after they had completed the post breeding moult. All geese departing Saltholm did so at low altitude (mean 25 maximum 240 in August); only one individual ever traversed a runway approach (on a single occasion) and did so well below aircraft flight altitude. During the period that the geese spent in the region, they flew at an average altitude of 57 (maximum 451 until their departure to winter quarters in October. Hence, despite their abundance and movements in the local proximity of the airport, these 10 individuals presented no hazard to air traffic. We should be extremely prudent about concluding that the movements of 10 tagged geese represent the typical movements of the 7000 barnacle geese present here in the late summer period. However, these data provide a useful insight into their movements and the risks that they present to bird strikes at the airport that will be important when undertaking an overall risk assessment of their presence and activity.Managing geese onsiteManaging grass infields and removing water bodies to reduce goose habitat useMost airports in Europe and North America maintain extensive areas of grassland between runways and taxiways to ensure pilot and general visibility, allow for emergency passage of aircraft straying from paved areas and enable rapid access for emergency vehicles to all areas (Washburn and Seamans 2004, 2013). However, very short mown grassland attracts insectivorous flocking avian species (such as European starlings Sturnus vulgaris, gulls and shorebirds; Brough and Bridgman 1980). Furthermore, because geese forage on grass swards that have relatively high digestible protein content and are low in structural carbohydrates (Sedinger 1997; Fox et al. 2017), the shortest mown turf swards are highly attractive to them. Northern Hemisphere geese tend to forage on grazed or cut swards less than 15 high, so maintenance of tall (18 high) sward may render such areas less attractive to geese, especially if seedheads are allowed to form. Cleary and Dolbeer 2005; De Vault et al. 2012; and Seamans 2004, 2013), because Seamans et al. (1999) observed no difference in goose use of swards that were 4 compared to 16 high. Furthermore, there are situations where it is not feasible to develop tall swards where short grassland remains a necessity between the taxiways and runways for visibility of lights and information signs, where tall grass is unattainable because of site conditions (for example, where restricted by climate, as in Iceland) or where complex interacting factors necessitate compromise to determine best management practices for mitigating multispecies bird strike risks (Blackwell et al. 2013a). Conover 1991; Washburn et al. 2007; Washburn and Seamans 2013), while other efforts minimise the nutritional returns for geese; researchers in one study found that endophyte infected turf type tall fescue Festuca arundinacea was less attractive to captive geese compared to perennial rye grass Lolium perenne and white clover Trifolium repens (Washburn et al. 2007). However, once a sward of a specific unpalatable grass species is established, it may require intensive management and reseeding to maintain in the face of recolonization by other grass species of higher palatability to geese (Washburn 2012). Riddington et al. 1997). Gay et al. 1987). Mason and Clark 1995; van Liere et al. 2009; Ayers et al. 2010). Inoculation of grasses with endophytic fungi that produce alkaloids has been successful in reducing non native Canada geese at New Zealand airports (Pennell and Rolston 2013). Copenhagen Airport is in the process of reseeding with a mixture of tall fescue F. arundinacea and perennial rye grass L. perenne inoculated with a high content of such endophytes, but this approach has not been applied on a sufficiently large scale at airports to date to judge its effectiveness. water bodies; Blackwell et al. 2013b) should be removed, if at all possible. If removal is not feasible, effort should be made to exclude geese, either by netting the wetland or establishing vegetation along the margin of the waterbody. Physical barriers along the water edge, such as a fence, may also prevent geese from using such open water. Guidance on implementation of such measures can be found in Conover and Kania (1991), Allan et al. (1995) and Smith et al. (1999).Active controlDespite all attempts to create a landscape that is as unattractive as possible to geese, in situations where geese land on airports, managers can employ a range of measures to disturb and displace geese away from the vicinity of arriving and departing aircraft. trained dogs and large birds of prey, see Hrom 2013). The use of infrasound has been suggested but its effectiveness is not proven (Gilsdorf et al. 2002; Fidgen et al. 2005). Birds cannot hear in the ultrasound range, so this has been shown to be ineffective for avian scaring (Dooling 1982; Bomford and O 1990). Aguilera et al. 1991) represents important tools exploited by airports against geese. However, regular and especially predictable use of any such techniques (even alarm calls and strong lasers) will result in habituation (although in one study, Canada geese showed no habituation over a period of 100 Whitford 2008). This necessitates that such methods are integrated into a cohesive strategy that incorporates their use in combination with lethal control (see below) and other techniques (Christensen et al. 2015b). Carter 2000; Castelli and Sleggs 2000; Froneman and Rooyen 2003; Allan 2006).Lethal controlWaterfowl are known to alter their distribution in response to hunting pressure (Fox and Madsen 1997; Madsen 1998), and the judicious use of lethal control can emulate a hunting environment around an airport. Lethal control may also serve to remove problem birds from the area. Many airports adhere to regulatory guidance by removing geese by lethal means onsite (mostly by shooting) as a last line of defence, although its use is highly dependent on location and operational constraints.Managing geese offsiteManagement of habitats and the geese on the airfield alone is insufficient for alleviating the risk of a strike because geese will still pass through the airspace above the site and through the departure and approach corridors as they move between habitats in the vicinity of the airport. While the management of onsite geese can be intensive and targeted, and is largely at the discretion of the airport operator, the management of offsite geese requires significant collaboration with multiple stakeholders. The International Civil Aviation Organisation (ICAO) recommends a 13 km radius safety zone around an airport centre point for the basis of an effective wildlife management plan (ICAO 2012). Existing guidelines also provide advice on how to avoid attracting bird hazards within this area (ICAO 2002). In some cases, the actions necessary to achieve effective goose management may be in opposition to current land use or undesirable to the stakeholder responsible for the land in question.In urban areas, open lawns and water bodies are publicly desirable amenities, and also increase the risk of attracting geese to the vicinity of the airport (Fox et al. 2013). Likewise, agricultural crop production can represent the mainstay of local farm economies but may increase the density of geese near an airport (Blackwell et al. 2009). In some cases, airports are able to extend the intensive management of geese outside their perimeter fences. For example, lesser snow geese Chen caerulescens caerulescens nesting in the Russian arctic migrate along the Pacific Coast in fall to wintering areas in British Columbia (Canada), Washington, Oregon and California (United States of America). Migration is prolonged from October to December, and thousands of birds remain on the Fraser River delta (British Columbia) all winter (Boyd 1995), in inter tidal marshes directly adjacent to the Vancouver International Airport. These geese represent an offsite risk to aircraft using the airport. However, in this case, agricultural habitats outside the airport operating area were proposed to contribute to mitigating the strike risk for aircraft by providing undisturbed offsite foraging areas as refuge for snow geese displaced from foreshore marsh areas. persistent disturbance) would result in a functional exclusion of the birds from the foreshore marsh. This combination of mechanisms has been successful in maintaining goose wintering concentrations in agricultural fields well away from the airport (Bradbeer 2007). This experience underlines the results of studies of scaring from sensitive agricultural areas, namely scaring works most effectively for geese if developed in conjunction with the provision of safe haven refuges to which birds can be displaced and left to feed in peace (Hake et al. 2010; Kristiansen et al. 2005; Fox et al. 2017). Placement of sacrificial lure crops is critical in relation to loafing/roosting/drinking sites to ensure goose flight lines do not cross aircraft approach and departure corridors (Baxter and Robinson 2007).Long term management agreements with local land owners can be used as a mechanism for reducing the availability of attractive habitats around an airport. In the Netherlands, outside of Amsterdam, Schiphol International Airport is surrounded by thousands of acres of productive farmland. In former times, the post harvest fields provided an abundance of crop residues, including cereals and vegetables, which attracted barnacle and greylag geese Anser anser, as well as other species of herbivorous waterfowl. To mitigate the risk of foraging geese in the vicinity of the airport, officials from Schiphol engaged their farming neighbours and entered into legal agreements that ensured all crop residues were tilled into the soil less than 48 after harvest. In combination with population control, land management and use of technology in active control, the fields were attractive to geese only for a very few days, compared to previously when they attracted geese for several weeks (B. Straver pers. comm.). Monitoring of goose movements was undertaken using radar before and after the agreement was reached between Schiphol and local farmers, and these data showed a reduction in the number of goose movements over the airfield (van der Meide and Pieterse 2013).Despite these examples, airports generally have exerted little influence on existing land use within airport safety zones outside the areas of their jurisdiction. Within such areas, influencing traditional agricultural practices through consultation with large numbers of private landowners and occupiers in extensive surrounding areas represents a major challenge. In contrast, airports are probably more successful in wielding influence through regional planning to avoid new developments that may affect bird occurrence (such as rubbish tips that might attract gulls). As lakes and wetlands are likely to attract geese and other waterfowl for foraging, loafing and night roosts, objection to new wetland restoration projects has been both