Wildlife in Airport Environments: Preventing Animal–Aircraft Collisions through Science-Based Management

12: Understanding Animal Movements at and near Airports

Understanding movements of hazardous wildlife species at and near airports is critical to formulating effective management strategies for reducing aviation risk. Animal movements vary daily, seasonally , and annually and are based on broad biological and ecological concepts, including foraging, reproduction, habitat characteristics, dispersal, and migration. As an energy conservation strategy, most animals minimize their movements to meet life requisites, which in turn presumably improves fitness. Animal movements in relation to airports can be direct; for example, Canada geese (Branta canadensis) flying onto an airfield because grass height and composition are suitable for loafing sites and as food. Animal movements in and around airports can also be indirect; for example, airports near large rivers may experience increased numbers of birds flying overhead during spring and autumn migrations, as rivers often facilitate bird navigation. In this chapter we describe ecologically based patterns of animal movements and develop a mechanistic foundation for understanding those movements and the degree to which we can modify them to reduce corresponding hazards to aircraft. We discuss biological and ecological causes of animal movements and some of the foundational ecological theories that help explain animal movements at airports. We then discuss motivations of animal movements at airports based on resource needs, the role of spatial scale when considering animal movements, and how to apply these concepts to reduce wildlife strikes. We end with a brief description of primary techniques to quantify animal movements, summarize management of animal movements at airports, and suggest areas of future research. Types of Animal Movements Animal movements can be divided into six broad, ecologically based categories: foraging, movements to rest sites, reproduction, territory defense, dispersal, and migration. We generally define foraging as any animal movement to feed, to obtain free water for drinking, or to search for food. Movements to rest sites are those where animals are seeking shelter (e.g., night roosts for turkey vultures [Cathartes aura] or bedding sites for white-tailed deer [Odocoileus virginianus]). Reproduction movements are associated with individuals searching for mates during a defined breeding season (e.g., white-tailed deer during the rut). Defense movements are those in which an animal is defending either a territory or a specific resource (e.g., food) from conspecifics or other animals. Dispersal includes movements of juvenile individuals traveling from their natal range to locate new areas to occupy (Greenwood 1980, Waser and Jones 1983, Clutton-Brock 1989, Waser 1996). Migrations are typically biannual movements of animals in response to changes in resource availability and for reproduction; for example, the spring and fall migrations of many bird species (Drent et al. 2003, van Wijk et al. 2012). These categories of movement vary temporally and spatially. Foraging occurs at least daily for most species, whereas migration typically ocJerrold L. Belant Brian E. Washburn Travis L. DeVault Understanding Animal Movements at and near Airports 12 130 wildlife monitoring curs twice annually, and dispersal by definition occurs once in a lifetime. In a spatial context, movements for foraging tend to be more restricted than movements to rest sites (but not always), which in turn are more restricted than defense and reproduction, dispersal, and migration. These categories can also be hierarchical; for example, foraging tends to occur during reproduction , dispersal, and migration. During the nesting and young-rearing periods, most adult birds and many mammals behave as central place foragers (Orians and Pearson 1979, Kacelnik 1984, Olsson et al. 2008, Wakefield et al. 2009), in that they return repeatedly to the nest or den site to provision young with food obtained during foraging bouts. For birds, these movements can vary in frequency and duration among incubation, chick-rearing, and postfledging periods. The mean daily number of visits to a landfill by radio-tagged, nesting herring gulls (Larus argentatus) generally increased in frequency and duration from incubation to postfledging periods—a consequence of energy demands of the chicks and reduced tenacity to the nest site after the young fledged (Belant et al. 1993; Fig. 12.1). These movements can in turn influence use of airports, either directly through increased foraging bouts during chick rearing or indirectly as birds fly over the airport to seek resources. Wildlife managers must consider that how, when, and where animal movements occur are based fundamentally in natural selection. Animals use resources (e.g., food, rest sites, mates) to help ensure their survival ; greater survival will often result in greater recruitment of young, which is how species persist. Success is based...