Knowledge of population processes and parameters, activity patterns, abundance, life requirements and resource use of pigeons (Fitzwater 1970; Godin 1994; Johnson 2000) influences the choice and placement of control structures as well as their efficacy at reducing the population (Seamans et al. 2013). Furthermore, numerous studies (Seamans et al. 2003; Dinetti 2006; Giunchi et al. 2012) have noted the positive benefits of integrated pest management, rather than a single method of control (Shea et al. 2000). Control methods focused on multiple scare devices such as Eagle Eyes and Fire Flags combined with habitat modification (Booth 1994) and limiting ecological resources (Giunchi et al. 2012) appear to result in the successful reduction of pigeon populations (Seamans et al. 2003). This was found to be true on the Muckleneuk campus as the pigeon population index declined by 50% as a result of the various control structures placed on the campus buildings. However, few studies have quantified the efficacy that different control structures contribute to the overall decline in a pigeon population index. Instead control structures are recommended based upon informal reviews and incidental observations (Seamans et al. 2007; Fukuda et al. 2008), whereas our study found the different control structures to be significantly different in efficacy.
The efficacy of bird spikes to reduce the pigeon population index on campus was significantly different from the other control methods, and thus the null hypothesis was rejected. Bird spikes were found to be the most successful in reducing the pigeon population (nearly 70%) as pigeons were physically hindered from perching on the treated building. Seamans et al. (2007) described similar findings at an airport; their research found http://buglessbeds.co.uk/south-london/abbey-wood-se2/bed-bugs-control-websites.php the anti-perching spikes to be effective against preventing pigeons from perching on buildings. Based on biological principles, the spikes deny access to sites selected by pigeons (Harris and Davies 1998). Nonetheless faeces and debris caught in the spikes can render them redundant and ineffective (Barnes 1997) when pigeons build their nests on top of this accumulation. Ongoing maintenance and monitoring is therefore essential to retain efficacy.
Scare devices such as Fire Flags and Eagle Eyes are considered to have limited efficacy at reducing pigeon populations (Harris and Davies 1998; Fukuda et al. 2008). This was found to be the case with the units placed on the Muckleneuk campus. There is much literature that describes habituation to the units as a limiting factor of visual deterrents (Godin 1994; Harris and Davies 1998). Due to the interdisciplinary nature of this study, the human component of staff on campus influenced the efficacy of the Eagle Eyes and Fire Flags as a number of units were removed and vandalised during the course of this study thus resulting in less than optimal unit placement and quantity.
Research conducted on structures with similar deterrent components to Fire Flags such as reflecting tape (Bruggers et al. 1986; Harris and Davies 1998), mylar ribbon (Tobin et al. 1988) and metallic streamers (Christensen 1996) describes similar findings of their inefficiency at deterring bird species. Furthermore, Harris and Davies (1998) point out the lack of biological basis regarding the Fire Flags and the limited application in deterring birds from areas. In fact, Fire Flags were found to be the least efficient control structure (33%), and did significantly differ from bird spikes and the combination.
Eagle Eye units were also found to have limited efficacy at reducing the pigeon population index on campus, and differed significantly from the bird spikes. Research conducted on a similar European device, Peaceful Pyramid, supported these findings as the reflecting mirrors were only marginally effective at altering pigeon behaviour (Seamans et al. 2003; Fukuda et al. 2008). According to the companys literature, the Eagle Eye unit has been successfully used to deter various avian species, including pigeons (Eagle Eye 2015), but the efficacy of Eagle Eye units has thus far been based on subjective estimates and anecdotal reports. The limited efficacy can be attributed to habituation to the units (Fukuda et al. 2008; Giunchi et al. 2012). In other avian studies, flashing lights and mirrors, the fundamental control attributes of the Eagle Eye units, were also found to be ineffective (Seamans et al. 2001) at deterring birds in urban environments.
The pest control industry recommends a combination of Eagle Eyes, Fire Flags and bird spikes in order to achieve maximum efficacy at reducing pigeon populations. According to the literature supplied by Eagle Eye (2015), a reduction of up to 80% of pigeon populations can be expected. In spite of this, the combination applied to the Samuel Pauw building was less successful than the spikes-only application on another building, but significantly different from Eagle Eye and Fire Flag units. This is in contrast to the assumption that the combination would be more effective than its individual parts. However, it should be mentioned here that the building on which the combination was applied had numerous open exterior cabling ducts and open or loose exterior ceiling boards. These provided the pigeons with alternative sites to the spikes which reduced the perching surface area of the balcony ledges, consequently limiting the effect of the combination on the pigeon population index. According to Jerolmack (2008), the life-sustaining processes of pigeons are often ignored when control measures are implemented. The combination of methods used on the Samuel Pauw building supports this view, as the carrying capacity of the pigeon population index was not optimally reduced for this building due to the availability of alternative untreated space on the building. The combination did, however, differ significantly from the bird spikes and Fire Flags.
Further replications of the pigeon control measures on numerous buildings would have improved the possibility of repeated results, however due to building access and financial implications; this study was limited to building availability.
On a larger scale, pigeon control does not influence the actual population size (Krimowa 2012) but simply displaces individuals away from the deterring systems to untreated buildings or sites (Mooallem 2006; Geigenfeind 2013). Nevertheless, a decline in the pigeon population index on campus after the control structures were implemented was noted and a 23% reduction in the pigeon population index between the baseline year and the management year on the untreated building occurred. It can therefore be inferred that no pigeons which previously inhabited the treated buildings moved to the untreated control building.
Another contributing factor which affects the effectiveness of avian deterrents is seasonality (Seamans et al. 2013). Climatic conditions, environmental changes and food availability all have an influence on the behaviour of pigeons and their subsequent tolerance of control structures. The efficacy of structures was found to increase during the warmer months corresponding with the natural pigeon population index fluctuation on campus (spring ((bartextx)=365 pigeons; SE=4) and summer ((bartextx)=367 pigeons; SE=8) seasons in comparison to the autumn ((bartextx)=342 pigeons; SE=8) and winter ((bartextx)=300 pigeons; SE=3) seasons) (Harris et al. 2016). Pigeons on the Muckleneuk campus which breed year-round with a peak between July and October (Harris et al. 2016), indicated a higher tenacity for tolerating the control structures in spring. According to Curio and Regelmann (1983), there is https://www.epa.gov/bedbugs a trade-off between conflicting demands in great tits, and this study too found that pigeons on campus were willing to endure the discomfort of deterrents in order to rear their young. Wildlife regularly makes decisions that are crucial to their survival and fitness (Conradt and Roper 2005). This was evident with the pigeons on the Muckleneuk campus as the population index on the campus buildings were found to be inversely related to the availability of their main food source, agricultural crops (Harris et al. 2016). Pigeons on campus rather directed their energy into foraging locally than travelling to surrounding agricultural areas in spring due to the limited crop availability (Harris et al. 2016). As a result more pigeons were visible on the buildings. The higher spring population index in the visual deterrents may also imply that the structures installed may ultimately not impact on pigeons behaviour in a significant way.
Even though Eagle Eyes, Fire Flags and the combination of control structures presented an irritant to the pigeons inhabiting the buildings, pigeons were willing to tolerate the discomfort. As a result the seasonal efficacy of these measures was low. This is in contrast to the bird spikes installed on the Cas van Vuuren building which did not provide any additional perching space in the form of exterior cabling or open ceiling boards. Pigeons were physically unable to perch on the balcony ledge where bird spikes had been placed, which resulted in a high seasonal efficacy at reducing the pigeon population index.
All control structures on the campus buildings were found to be the least efficient during the autumn months. According to Pulliam (1976) and McCleery (1978), different behavioural options of wildlife result in a continual shift in relative costs and benefits. Due to the colder temperatures, pigeons were hidden as a result of thermal factors (Harris et al. 2016) and consequentially also from the observer. Autumn also coincides with a biologically important season in the pigeon life cycle, namely moulting. As costly energy is diverted for feather regrowth and plumage change (Murton 1966; Johnston and Janiga 1995), pigeons are relatively inactive as opposed to the rest of the year in order to conserve energy.
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