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

3: Effectiveness of Chemical Repellents in Managing Birds at Airports

Repellents include methods and devices used to manipulate behavior of animals to reduce damage or nuisance. Critical to the design and success of repellents is understanding how sensory modalities mediate perception of signals, and how ecological context and sensory inputs influence animal learning. A repellent’s success is tied to the axiom of using the proper tool for the proper job. When repellents “fail,” it is almost always because wildlife managers have not appropriately matched signal, receiving systems, message, and context. Reconciling such considerations can be a complex process. In this chapter we review components and processes essential for the successful use of repellents for managing birds at airports. There is often great disappointment among managers on the performance of repellents, and chemical repellents may be among the most misunderstood wildlife management tools. Perceived failures of chemical repellents are not always accurate, as performance is aligned with the sensory biology of the target animal and context of application. Successful use of repellents requires (1)understandingtherulesofanimallearning;(2)understanding the sensory abilities of targeted animals; (3) appreciating that repellents are tools to shape and modify behavior,nottoxicants;(4)understandingthatrepellents train individual animals and that, when populations turn over frequently, constant training may be required; and (5) understanding that repellents work best if alternative resources or places are available, and that if alternatives are not available, the animal may endure unpleasant side effects. In short, large numbers of animals with no alternative resources or places to go will swamp the defensive characteristics of a repellent. Given use based on the requisitesdescribedabove ,repellentscanbeeffectiveanddeserveaplaceinintegratedandadaptivepestmanagement strategies. The reviews on these topics should be sought forin-depthcoverage(GarciaandHankins1977;Revusky 1977; Dooling 1982; Kare and Brand 1986; Clark 1997, 1998b; Mason and Clark 1997, 2000; Reidinger 1997; Domjan 1998; Conover 2002; Werner and Clark 2003). Mediating Sensory Modalities Mediating sensory modalities in birds includes the chemical senses (smell or olfaction, taste or gustation, irritation), hearing or audition, vision, and touch (see also Chapters 2 and 4). In general, birds have excellent auditory and visual capabilities and moderately developed chemical senses (Mason and Clark 2000, Walsh and Milner 2011). Olfaction acts as a telereceptive system capable of receiving airborne chemical stimuli in extreme dilution over relatively great distances. Olfactory cues may generally orient some bird species toward food sources (e.g., Stager 1964, Verheyden and Jouventin 1994) or elicit specific discrimination behaviors from others (e.g., Clark and Mason 1987, Roper 1999). Gustation requires more intimate contact between the source of the signal and the receptors. Taste receptors in birds are located throughout the oral and pharyngeal cavities, and generally mediate sensory qualities also perceived by mammals: sweetness, saltiness, sourness, and bitterLarry Clark Michael L. Avery Effectiveness of Chemical Repellents in Managing Birds at Airports 3 26 wildlife management techniques ness (Kare and Brand 1986). Bird species perceive taste qualities differently, however, reflecting their speciesspeci fic ecologies and food habits (Berkhoudt 1985). Chemesthesis is the perception of chemically irritating or painful stimuli. Noxious chemical stimuli may give rise to qualities such as stabbing, throbbing, burning, or itching, depending on the specific nociceptive fiber that is stimulated and the neurotransmitter released (Clark 1998a). Vision, like olfaction, is a telereceptive system (Zeigler and Bischof 1993). Unlike olfaction, the source of visual cues is more readily identified because of the linear relationship between source and receptor. Visual cues facilitate navigation, recognition of conspeci fics and mates, predator avoidance, and food selection (Chapter 2). Sounds provide birds with information regarding territorial defense, mate selection, navigation, and recognition of predators, conspecifics, and prey location (Gill 1990, Beason 2004; Chapter 4). The sense of touch is integral to the feeding behavior of many birds, particularly many waders and shorebirds (Gill 1990; Chapter 4). Furthermore, while birds are flying, feathers are constantly being adjusted in response to tactile sensations received via nerves at the base of the shafts. Types of Chemical Repellents There are two fundamental repellent classes: primary and secondary (Clark 1997). A repellent is classified as primary or secondary based on the physiological mode of action and whether avoidance behavior is learned. Primary repellents possess a quality (e.g., unpalatable taste, odor, irritation) that evokes reflexive withdrawal or escape behavior. Secondary repellents evoke an adverse physiological effect (e.g., illness), which the animal associates with a sensory cue (e.g., taste, odor, visual cue) and then learns to avoid. These definitions help to quickly assess the likely effectiveness of a chemical repellent in a particular...