On the epidemiology, biology and food-dependent reproduction of the feral pigeon (Columba livia)

Millions of feral pigeons (Columba livia, Gmelin 1789) live in close association with the human population in our cities. They have managed to adapt extremely well to city life. The partial absence of an effective regulation by enemies and the rich food basis in urban habitats allows the development and maintenance of large feral pigeon populations. These, however, can cause various problems such as fouling with feces, and the transmission of pathogenic microorganisms and parasites to humans. While many wild-living species have a parasitic fauna comparable to that of feral pigeons, no other species lives as close to humans and offers that many possibilities of transmission. Feral pigeons breeding and roosting close to human lodgings thus pose a serious health risk, which is why many homeowners try to protect themselves by repelling the birds from their house facades, window ledges and balconies.
New pigeon proofing systems are regularly introduced onto the market, but scientific proof of efficacy and a statement regarding their use from the point of view of animal welfare is usually lacking. We therefore evaluated the effectiveness of two gel repellents on free ranging feral pigeons in an experimental pigeon loft. The gels used an alleged tactile or visual aversion of the birds, reinforced by additional sensory cues. This study concludes that both gels show a restricted, transient repellent effect, but fail to prove the claimed complete effectiveness. In addition, the adhesive effect of the gels conflicts with animal welfare concerns because gluing of plumage presents a serious risk to feral pigeons and also to other non-target birds. The repellent gels are therefore not suitable for feral pigeon management in urban areas.
Additionally, an overview of the most essential pigeon proofing systems is provided within the frame of this thesis. It discusses the advantages and disadvantages of the most widespread systems and further sets the focus on animal welfare issues. The overview points out that even initially harmless and animal friendly proofing systems might become dangerous to the birds over time if they are not regularly maintained. It further highlights how important it is to scientifically test each system before usage. Moreover, this outline supports the recommendation that each system should come with a proper installation and maintenance guide when it is introduced onto the market. If untested systems are being put to the test by unknowing end users, they might endanger the birds. Additionally, uninformed homeowners violate the animal protection law if a system harms an animal, even if this happens with no ill intent.
In a further study, we examined the effect of a sudden decrease in the natural food basis on the reproduction of a well-studied feral pigeon breeding colony. Despite the known fact that food shortage is a major source of reproductive failure in feral pigeons, it was still unclear at which phase of the reproductive cycle it reduces overall reproductive success. The findings of this study imply that the number of broods per pair decreased significantly under food reduction, while the hatching success remained more or less constant. However, a significantly greater number of nestlings died during the costly rearing phase. Results suggest that the high energy demand of the fast growing feral pigeon nestlings cannot be met under food scarcity. The decreased number of broods and the limited fledging success consequently reduce the total number of fledged young by more than half, which finally leads to a decrease in colony size.
Another negative side effect of large feral pigeon populations, maintained through the abundant anthropogenic nutritional basis in urban surroundings, is the overcrowding at breeding places. From an epidemiological point of view, these high population densities can increase the transmission of pathogenic microorganisms and parasites, such as the pigeon tick Argas reflexus. The medically and veterinary important A. reflexus usually feeds on pigeons, but if a natural host is not available, it also enters dwellings to bite humans who can respond with severe allergic reactions including anaphylactic shock. The pigeon tick is ecologically extremely successful due to certain outstanding morphological, physiological, and ethological features. Yet, until today, it was still unclear how it finds its hosts. In the main study, we tested different host stimuli, such as living nestlings as well as begging calls, body heat, smell, host breath and pigeon tick feces, under controlled laboratory conditions. Of all stimuli tested, only heat seemed to play a central role in host-finding. Subsequently, the crucial heat stimulus was tested under natural conditions within a pigeon loft. The results demonstrated that the host finding ability of A. reflexus is restricted to only a few centimeters. We concluded that this ectoparasite finds its host by random movements and recognizes it only shortly before direct contact is made. These findings are useful for the control of A. reflexus in infested apartments, both to diagnose an infestation and to perform successful monitoring after disinfestation.
The aim of this thesis was to provide important insights into the epidemiology, biology and food-dependent reproduction of the feral pigeon. With these findings we hope to contribute to the healthier coexistence of feral pigeons and humans in urban habitats.