Integrative Biology

Problem animals – feral pigeons and wild boars

A. Transmission of Chlamydophila psittaci from feral pigeons to humans in the urban environment

Feral pigeons (Columba livia) are known to be chronically infected with the obligate intracellular bacterium Chlamydophila (C.) psittaci, the pathogenic agent of avian chlamydiosis and human ornithosis/psittacosis. The infectious chlamydial elementary bodies are shed either by respiratory or ocular secretions or by faeces if intestinal organs are involved. Up to the present, more than a hundred cases of transmission of C. psittaci from feral pigeons to humans have been published. We suppose that additionally a high number of C. psittaci infections have either been misdiagnosed due to general influenza-like symptoms, remained unreported, or feral pigeons have not been recognized as a source of infection. We are assessing the zoonotic risk posed by C. psittaci in the public area of Basel by repeatedly analyzing pharyngeal- and cloacal swab samples from the feral pigeons in our lofts as well as faecal samples taken in public areas. Swabs and faecal samples are tested using a well-established species-specific nested-PCR assay targeting the ompA-gene of C. psittaci. Up to now, our results are consistent with previous publications (Magnino et al., 2009) and show that about 2.5% of the feral pigeons in our lofts are shedding C. psittaci into the environment. It could also be demonstrated, that chlamydial shedding occurs in fact intermittently, since some of the affected individual birds could be tested on multiple occasions with varying results. With our study we contribute to a risk assessment for human C. psittaci infections by feral pigeons in the urban environment.

B. Population dynamics of the feral pigeon (Columba livia) and management implications

In our public feral pigeon lofts we have the unique opportunity to study the population dynamics of feral pigeons under natural conditions. We are collecting relevant data in a long-term study, which gives us insight into seasonal variations in breeding activity and breeding success. Thus, we can correlate the breeding activity to seasonal influences, the occurrence of diseases and parasites, other factors and special events. Additionally, we are able to gain insight into the dynamics of parasite infestations, and we have direct access to parasites that can also infest humans. The aim of our study is to obtain more knowledge about the feral pigeon population dynamics and thus to contribute to an improvement of feral pigeon management strategies.

C. Investigation of the effectiveness of deterrent systems against wild boars (Sus scrofa)

During the last two decades wild boar populations have grown rapidly and the range of the species has increased steadily, covering almost the whole European continent today. Wild boars cause considerable damage to fields and grassland, but also pose a potentially high threat to livestock, as carriers of the pathogen of the classical swine fever, which may be transmitted to domestic pigs and can cause huge losses (Fig. 2). Together with the regulation of the populations by means of hunting, the protection of fields and livestock is therefore crucial for preventing major economic losses. Field protection is normally achieved by putting up electric fences. However, these are expensive and require regular maintenance to provide for functioning, which is time-intensive. Alternatively, several deterrent systems basing on optic-, acoustic-, olfactory-, and gustative effects are available, most of which are lacking scientific proof of efficacy. In our study we investigate the effectiveness and the sustainability of several deterrent systems in field experiments with free ranging wild boars. Deterrents investigated were solar blinkers, an odor repellent imitating a mixture of stenches of several predators, and a gustative repellent that claims to deter wild boars by its acetous taste. Preliminary results suggest that wild boars behave very cautiously concerning changes in their natural habitat. After a short period of neophobic effect, deterrent systems lose their effectiveness and wild boars surmount the optic, olfactory, and gustative barriers regularly. At the moment, we are investigating a self-constructed deterrent system that combines acoustic and optic effects. Our first results in the field are satisfying, however, it remains to be seen, whether the deterrent effect is sustainable. Our results contribute to an assessment of legal foundations and common practice of hunting, field protection, and compensation payments by cantonal veterinary- and game authorities.

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