Loved or loathed, feral pigeons as subjects in ecological and social research (2024)

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Abstract

Introduction

This essay promotes the feral pigeon (Columba livia) as an important subject for urban ecological and social science research. This position came about during an urban ecology study on pigeons in Butte, Montana. During our work, we realized the remarkable place pigeons have in the urban environment. We suggest that a change in attitude toward and an increase in scientific focus on pigeons could enhance the field of urban ecology in a variety of ways. Throughout this essay, we focus on the role of the feral pigeon as a missing link in ecological studies specifically in urban environments, as a global and local environmental indicator, and as a valuable subject for citizen-science-based projects.

Non-native species, especially non-native birds, are often understudied (Seymour 2013). Similarly, species of abundance are often overlooked in research, likely because of their commonality, and underfunded, likely because of a lack of urgency (Hamilton 2008). These two conditions place the pigeon, along with a few other avian species, as nearly invisible in ecological research, other than in the context of ecological problems and population reduction. Yet the pigeon is a global species that carries with it a wealth of information that can be studied at the local level. Audubon magazine’s March/April (2013) edition, entitled: ‘Why Birds Matter’; elaborates by highlighting topics such as understanding animals’ social behavior, avian habitat changes and using birds as both disease indicators and indices of environmental health. The magazine points to pigeons as a species that can help detect poor air quality (Berger 2013; see also: Schilderman etal. 1997), supporting the concept that the birds may serve as reliable environmental indicators (Morrison 1986). Our position occurs at the intersection of these assertions: the feral pigeon is a surprisingly understudied animal ecologically but one that holds great potential for providing information about local and global urban environments. Compared with other well-populated invasive species, such as the House Sparrow (Passer domesticus) and European Starling (Sturnus vulgaris), pigeons are easier to identify as a species, as individuals, from a distance and track in their home range.

Of equal importance is the role that human interest plays in conservation, a key component in the urban ecology discourse. People’s value of nature, how they expect an environment to be managed, and how people effect or are affected by management policies, increasingly relies on citizen science research. Steiner (2016) discusses the importance of stewardship and points to the role of understanding as critical components in sound planning. A budding argument exists for using species such as the pigeon and house sparrows (Passer domesticus) in ecological stewardship and citizen-science-based activities (Dunn etal. 2006; Larson, Cooper, and Hauber 2016). We build on this position to promote using the pigeon to help people connect to urban stewardship in both ecological and social frameworks.

In many ways, the position to advocate for the pigeon is an uncomfortable one. Naturalists and environmentalists alike espouse sentiments for the bird that are unfavorable at best. The pigeon carries with it all that runs counter to ecology and conservation: these birds are feral, exotic and invasive. The birds are associated with habitat loss for native species and social concerns such as disease and filth. Named ‘rats of the sky’, pigeons are a flagship species of the human imprint on local biodiversity (Jerolmack 2008). It seems no wonder that pigeons are underrepresented in studies that examine their positive role in urban ecology. That said, much of the ecology and social reputation of pigeons stems from a fascinating history intricately tied to human development and gives credence to our position.

The wild type, or founder species to the common, urban or feral pigeon, is the rock pigeon of Eurasia, also: C. livia. The natural habitat of these birds is mixed grasslands for ground foraging and rocky cliff faces for nesting. The birds were domesticated over time, selectively bred for high, year-round egg production, meat and a strong attachment to their territories which aided in human communication via carrying messages back to their nesting sites (see Blechman 2006; Jerolmack 2013). As with most animal domestication, the individuals with the highest tolerance for humans had the greatest access to food which, in turn, led to reproductive advantages and a growth in populations (see Caras 1996; Trut 1999). So valuable were pigeons to humans that they were carried across the Atlantic Ocean to the New World (Blechman 2006; Jerolmack 2013). Today, feral pigeons live primarily in the urban environment around the world, feast largely on human food waste and can reproduce year-round.

The pigeon’s remarkable ability to live in human environments, especially the cityscape, is why we consider them a key species in urban ecology. A species that is both ubiquitous and abundant, the pigeon is a constant in nearly all urban environments. The pigeon’s cosmopolitan standing should give them a prominent status in ecological and social science research as it avails them to comparative studies in different geographic locations. We point to a body of work that we argue, could be improved upon with the inclusion of pigeons as a key component to understand certain ecological issues, such as environmental contaminants. This essay frames the pigeon as an important species for ecological research, society and the changing face of environmental conditions.

Ecological import

We began our research in Montana in response to Butte-Silver Bow County’s request to learn more about the feral pigeons residing in the central business district (CBD), ultimately as a means to initiate a management program. Our primary research focused on identifying and characterizing feral pigeon’s nest, roost and forage sites within the CBD and surrounding neighborhoods. We mapped the distribution of the birds, and, not surprisingly, found a strong connection between pigeons and specific human environments: vacant buildings, areas that had moderate protection from the elements, such as three-side wind breaks and overhead cover, and a steady food source, like restaurant waste (Capoccia, Boyle, and Darnell 2014). We also examined movement of individual pigeons between colonies, dispersal of juveniles from colonies and estimates of population size. While simple, this work provides baseline data for the population at hand and allows us to test different research techniques in terms of trapping, marking and re-sighting methods (Richardson, Capoccia, and Hart 2016).

One of our most unexpected findings was that the pigeon offers untapped research opportunities. Though not a true wildlife species, compared with other free-roaming animals, pigeons are often close at hand, easy to access and capture, and require minimal permits to handle. There are over 20 classifications of plumage variants which make visual identification particularly easy (Dunmore 1968). The pigeon provides opportunities to learn and experiment with a range of methods pertaining to population dynamics, animal behavior, ecological interactions and basic study design. Additionally, these birds are abundant and universal and, with increasing urbanization, we argue that it is important to observe the dynamics of a species that boasts such remarkable consistency in a range of geographies. Studying and tracking pigeon populations have the potential to elucidate shifts in environmental conditions, including environmental contaminants, avian disease, and climate change, that could provide insight into or forecast shifts in the regional biodiversity (see Hamilton 2008).

So established and integrated are these birds in urban and suburban environments that we argue they could be considered an urban keystone species. Pigeons are found on every continent except Antarctica; the magnitude of such a presence is accompanied by a major role in the way habitat is shaped and nutrients and minerals are cycled. For example, as a species that naturally evolved to digest seeds, pigeons are known agents of seed dispersal (Butcher and Bocco 2009) and provide connectivity between urban islands. Furthermore, a growing amount of research exists on the limiting factors present in an urban environment, such as noise, human activity and cover type, and these factors shape the diversity of species present in urban habitats (Luniak 2004; Fisher etal. 2016; Aronson etal. 2017). Not only is the pigeon a species that can thrive in an urban habitat but it is also contributes to the tropic levels in an urban ecosystem. They are effective as primary consumers to the extent that their population can support substantial predation and are an important food source for many birds of prey.

Countless publications highlight the pigeon as a key prey species for urban-dwelling raptors across the globe. For peregrine falcons (Falco peregrinus), in particular, Rejt (2001) estimated feral pigeons composed a year-round average of 32% of the diet in Warsaw, Poland with a peak of over 50 % in the winter and summer. A similar study in southwest England showed pigeons and doves made up 47% of the prey-base of peregrines, pointing to pigeons as a key species in the raptor’s diet (Derwit and Dixon 2008). In Brazil, pigeons make up 68.5% of the Peregrine diet in Porto Alegre and a stunning 80.9% in Santos (Silva 1997). Farther east, pigeons were shown as a favored species in the Peregrine diet in Patagonia, Ria Deseado, Argentina (Garcia, Bo, and Yorio 2014). In New York City, the estimate of pigeons as part of the peregrine’s diet is thought to reach peaks of 75% during certain time periods (Angier 1991; Cade 2016). Arizona reports having one of the strongest peregrine populations in the United States and asserts that even falcons that nest and roost away from urbanization come into cityscapes to feed on pigeons (AZGFD 2016). In addition to peregrine falcons, pigeons are reported as a key prey species for other birds of prey that include, but not limited to: 10% of the diet of urban common kestrels (Falco tinnunculus) (Yalden 1980), sharp shinned hawks (Accipter striatus) (Mueller and Berger 1970), coopers hawks (Accipiter cooperii) (Boal and Mannan 1999) and considered the ‘principle avian prey’ of most European goshawk (Accipiter gentilis) populations (Rutz etal. 2006: 580).

Given the domestic pigeon’s important role as a prey species, one might go so far as to argue that this bird filled the prey-base niche left by the Passenger Pigeon (Ectopistes migratorius) in North America. While these two species clearly differ in flock size, they share the family, Columbidae, much of the same forage type, and are known prey for the many of the same predator species (Halliday 1980). The pigeon we know today increased in presence over the last few hundred years, coming in the wake of the Passenger Pigeon’s decline and extinction in the early 1900s, offering the predators an alternative. In fact, evidence points to the fact that the population of Cooper’s hawk changed behavior to switch prey species from the Passenger Pigeon to our urban Pigeon (Dunne 2017). In addition, the Peregrine falcon, though marked by dichlorodiphenyltrichloroethane (DDT), is thought to have endured an earlier and much larger impact by the loss of its key prey, the Passenger Pigeon (Bodio 2010). It is worthwhile to speculate what the current accipiter and falcon population might look like if the Passenger Pigeon had met its fate without its urban successor.

The focus on feral pigeons as an important prey species could provide insight to and justification for advanced research on urban birds of prey, specifically regarding environmental contaminants and avian disease. As history illustrated with DDT, the bioaccumulation of environmental toxins has the potential to result in severe impacts on predatory bird populations. While the peregrine falcon is often the ambassador species for recovery, DDT’s impact was wide sweeping and affected a range of species from the bald eagle (Haliaeetus leucocephalus) to countless passerines (Henry 1977; Rattner 2009; Elliott etal. 2015). In the past few decades studies have found raptors with biological accumulations of lead (Burger 1995), polybrominated diphenyl ethers (PBDE) and polychlorinated biphenyls (PCB) (Park etal. 2009; Newsome 2010) to name a few. One study in particular examined raptor carcasses and hypothesized that the environmental contaminants were a result of bioaccumulation from the carbon source, though not cited as the cause of death (Elliott etal. 2015). The article stresses the fact that persistent organic pollution has the potential to biomagnify as trophic levels increase and goes on to detail urban expansion and agriculture as likely sources of chemicals including, but not limited to, PBDEs, PCBs, and 1,1-dichloroethylene (Elliott etal. 2015). As granivores that frequent agricultural areas as a food source, pigeons serve as a species that could make the link between the carbon source, parenthetically noted as ‘representative of a high-corn diet’ (p. 158), organic pollutants and upper-level predators.

A second study reports on the best samples to use in pan-continental trends in environmental contamination of birds of prey (Espin etal. 2016). The article addresses the challenge of sampling raptors based on their legal protection status and focuses on biological tissues, such as: feathers, preen oil, carcasses and crop-content food remains as alternative sampling methods with varying degrees of success. The authors cross-list eight alternative sample types at an impressive 35 locations across Europe and surrounding regions as means to show the geographic scope of the issue. While comprehensive, the paper lacks the attention to the prey base (other than in the context of scavenging), not the least of which is the pigeon, present in all of the 35 study regions, including Iceland. In both articles, the feral pigeon could have been an integral part of the research to map bioaccumulation of toxins, the results of which could go on to strengthen raptor-focused conservation agenda.

Feral pigeons also make excellent subjects to study other environmental scenarios such as avian diseases and climate change. West Nile Virus (WNV) and avian influenza, are known to infect pigeons and have the potential to be widespread; tracking pigeon populations could be a key mechanism to follow a pandemic. But even diseases that occur at a regional scale, including avian cholera, Escherichia coli (E. coli), histoplasmosis and Salmonella (ssp.), all of which are documented in pigeons, can cause substantial outbreaks and move between species (Botzler 1991; Panigrahy 1996; Gibbs etal. 2005; Cano-Terriza etal. 2015; Benedict and Mody 2016). The pigeon’s characteristics of being easy to find, track and having a year-round presence, lend well to early identification. Pedersen etal. (2006) tested pigeons in Fort Collins, Colorado, for E. coli and salmonella. While they did not detect E. coli, they did determine that 3.2%, of pigeons were positive for salmonella, which is consistent with the findings of Toro etal. (1999) from Santiago, Chile. The transmission of any these diseases between species is not unlikely. Phonaknguen etal. (2013) pointed out that pigeons and domestic chickens (Gallus gallus) have the potential to spread the H5N1 strain of avian influenza when the two species comingle. In a 6-year study in Brazil, Felippe etal. (2010) showed avian infectious bronchitis virus also moved between domestic chickens and pigeons. The same is true for cholera, histoplasmosis, salmonella and E. coli, which brings human health concerns into the picture.

These and other avian-based diseases can be exacerbated by fluctuations in environmental conditions such as increases in temperature and precipitation, factors that are subject to climate change. It is well-accepted that as environmental stressors increase, body condition tends to decrease which makes individuals more susceptible to disease. A study in Egypt showed that Columba livia naturally infected with H5N1 had a 50% mortality rate (Mansour 2014). Another study showed that, in an outbreak of WNV, while pigeons did not show statistically significant mortality, they have a 70% infection rate, which could then translate into high transmission rates (Bakonyi etal. 2013). Monitoring residential bird populations, combined with gathering data on environmental variables, like weather, is a great way to detect changes in populations that are often associated with the aforementioned diseases.

Regardless of the scenario, the feral pigeon offers a relatively consistent variable from which a host of ecological conditions can be studied. Pigeons are a standard subject that provide connectivity between places such as Beijing, China and Butte, Montana. The relationship pigeons create among urban environments could be considered a touchstone for ecological health. Literature on abundant species management refer to both native and exotic species as important populations from which to monitor general environmental conditions. Moreover, history reminds us that the decline of abundant species, particularly prey species, could result in a subsequent trophic cascade, so despite high numbers, the vulnerability of abundant populations should not be discounted (Hamilton 2008). In short, major oscillations in pigeon populations are uncommon. As a result, the bird’s omnipresence makes them an ideal study species because they provide consistent data that is less noisy and easier from which to draw inferences in scientific studies.

Citizen science and a link to conservation

As ecological management expands to include the urban landscape and human priorities we can, once again, turn to the pigeon for research. Local ecology, defined as the area closest the user, networks into larger ecological processes and informs us about our own habitat. When it comes to collecting data on the local and urban ecology, wildlife scientists often benefit from understanding the community knowledge of a given species (Cooper etal. 2007; Belt and Krausman 2012; Haywood, Parrish, and Dollivert 2016) and understanding the attitudes people have toward the animal species (McCleery etal. 2006). Though the outward view is that pigeons are problem animals linked to destruction of buildings and potential spread of disease, closer inspections reveal that it is quite common to find people who have a strong attachment to the birds, and others who simply feel pigeons belong in the area (see Jerolmack 2013; Capoccia, Boyle, and Darnell 2014). In fact, feral pigeons are viewed more similarly to other free-roaming wild animals than domestic ones and serve as a valuable link to the natural world, for good or for bad (Dunn etal. 2006; Jerolmack 2013; Capoccia, Boyle, and Darnell 2014).

People who favor pigeons are passionate about their presence to the extent that they know individual birds and feed whole flocks, aspects that contribute to the birds’ ecological carrying capacity. Many people know which directions pigeons come from in the mornings, where they head in the evenings, and even seasonal differences in these behaviors. In contrast, those who do not like pigeons remark about other components of the urban ecology, noting that they often see pigeons comingling with ravens or that they saw a fox or raptor by their house and hope it is preying on pigeons. In both cases, community members addressed pigeons as part of nature and show familiarity about behavior, population dynamics and even other species (Jerolmack 2013; Capoccia, Boyle, and Darnell 2014). The pigeon’s integration with nature aligns with work by Dunn etal. (2006) who state that feral pigeons are a significant connection between urbanites and the natural world. They go on to support the idea that the relationship to the natural world is critical for conservation, a position that is espoused by many scholars. In fact, Castree and Braun (1998) quote Neil Smith saying, ‘nature separate from society has no meaning’ (p. 6).

Attitudinal research on nature and conservation stems from citizen science and conservation. In fact, the discourse on human dimensions of natural resource management stresses the importance of understanding human attitudes and public involvement as they relate to wildlife, conservation and ecological management. Nowhere could this be more important than on the urban landscape where the general public become the stakeholders. People’s investment in pigeons shows relationships to nature and animals, where on the contrary, negative attitudes tend to reflect the degradation of the environment (Jerolmack 2013). McCleery etal. (2006) point out that people’s attitudes toward wildlife forecast human behaviors and that human value brings about motivation to support conservation efforts for a range of species.

For conservation to be a success we require widespread support of and participation in environmental stewardship. Calling upon the local community to track and record animal sightings is an excellent way to engage the public in science (Larson, Cooper, and Hauber 2016; Rudd etal. 2016). And, when it comes to collecting data on the local ecology, wildlife scientists often benefit from understanding the local knowledge of a given species and, in turn, community involvement improves stewardship (Belt and Krausman 2012; Haywood, Parrish, and Dollivert 2016). Larson, Cooper, and Hauber (2016) show the importance of citizen science monitoring house sparrows. They point out that understanding people’s emotions provides a link to how they value wildlife which can contribute to local ecology regulations. A complimentary study shows the importance of community perspectives in designing management plans for white-tailed deer in Pennsylvania. Improved communication between the general public and the wildlife specialists improved the satisfaction with the deer management plan (Fleegle, Rosenberry, and Wallingford 2013). Results from a citizen science project in California showed that community members excelled at identifying health problems in a local squirrel population. The community members were able to identify six different clinical signs of notoedric mange (Notoedres centrifera) in the squirrels and did so faster than the local officials (Rudd etal. 2016). Results are similarly impressive from studies on the health and population dynamics of mountain goats (Oreamnos americanus) in Glacier National Park, Montana, USA (Belt and Krausman 2012) and koala (Phascolarctos cinereus) in Australia (Predavec etal. 2016). In all cases, the authors report accuracy in species knowledge and comprehensive geographic coverage, information which the scientific team alone was unable to acquire.

Across the field of ecology there is an increasing emphasis on the importance of communities’ knowledge of population changes over time and even on individual animal sightings that may improve accuracy of territory data and population sizes. Collectively, these examples demonstrate the strength of human perspectives in ecological management and the importance of people’s investment in conservation issues. These finding help scientists and policy makers develop management plans by gaining a broader understanding of an areas biodiversity, the shifts in animal movement and how the social culture relates to nature (McCleery etal. 2006; Larson, Cooper, and Hauber 2016). Understanding a community’s tolerance level for a species helps inform the management protocol, especially with regard to population reduction (McCleery etal. 2006; Fleegle, Rosenberry, and Wallingford 2013; Larson, Cooper, and Hauber 2016). These studies validate the fact that social perspectives and urban ecology are both valuable for conservation and gaining traction in the arena of wildlife management.

Given the widespread distribution of pigeons, we argue that community efforts to monitor local pigeon populations would be an ideal way to link people into larger discussions on topics such as avian health or climate change. The pigeon could serve as a catalyst to start the discussion regarding people’s perspectives on the surrounding ecology as well as the nature of invasive species. The bird’s robust size, low flight response and seasonal omnipresence make them an ideal species for people to connect with. Their unique coloring and strong attachment to a territory help people identify individual birds and reduce over counting. And, as stated earlier, pigeons do not require excessive permitting, they are easy to handle, and can be marked using plastic colored leg bands made for the poultry industry, so their population can be tracked with remarkable ease and accuracy. The strong human–animal interactions that occur between pigeons and people could potentially be a staple for information on urban wildlife populations.

Conclusion

We have in no way exhausted all the avenues for research involving the feral pigeon. Pigeons serve as a reflection of our environmental impact and can be used to monitor the environmental condition. This bird is one of several species that mark human advancement: from early domestication to our own high-density living. As our environment continues to flux, a free-roaming and pervasive animal perches right outside our front door, sometimes literally, and provides an echo to our actions. While the pigeon’s presence initially represents a negative shift in biodiversity as an invasive species, its presence holds an important role in ecosystem function, not the least of which is the urban setting. Changes in the pigeon’s population can be used as an assessment of environmental conditions, and a way to connect local environments. In many ways, the pigeon is as urban as people are and may be our modern canary.

Pigeons have the potential to serve as a gateway species for scientists to explore the relationship people have with their local environment, and promote science and conservation. Well over a century ago, the human attachment to nature was espoused by George Perkins March, Man and Nature (1864), followed by Aldo Leopold, A Sand County Almanac (1949) and later, Roderick Nash, Wilderness and the American Mind (1964). Today, human interests remain a core part of contemporary conservation which turns to urban and suburban settings as emerging sites and citizen science for new methodological approaches (Decker, Brown, and Siemer 2005). As we continue to increase our collective understanding of our environment, we can take research into the future using the pigeon as a powerful lens to examine the urban dynamics of ecological needs.

Nature is not always the wild conditions promoted through places like natural parks, it can also be found in the trees that line urban streets (Cronon 1996; DeStefano 2010; Dunne 2017). Loved or loathed, pigeons have the ability to give us a much better understanding of urban wildlife interactions that could be relevant to a variety of other wildlife species and has the potential to vindicate the critical role urban ecology has on conservation at large.

Acknowledgements

Tremendous appreciation goes to Richard Douglass, Ed Randall, Dan Powers, Matt Vincent and Butte-Silver Bow County for their commitment to this project from the start. A special note of appreciation goes to those helped edit this work, especially Amy Kuenzi, Lindsay Torpey, Jay Sellmer and Cody Richardson. We also thank Montana Tech of the University of Montana for providing the institutional support for this manuscript. And to Bill and Asha Henne for being patient during this work.

Conflict of interest statement: None declared.

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© The Author(s) 2018. Published by Oxford University Press.

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