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Direct and indirect effects of anthropogenic bird food on population dynamics of a songbird
Abstract
Anthropogenic bird foods are frequently credited with affecting avian population dynamics, but few studies have tested this assertion over broad spatial scales. Human-derived foods could directly impact population sizes or indirectly affect them by mediating the influence of another factor, such as disease. In 1994, a novel disease outbreak (mycoplasmal conjunctivitis) substantially reduced populations of the house finch (Haemorhous mexicanus) in the eastern United States, creating an opportunity to test whether bird feeding indirectly exacerbated or ameliorated the impacts of the disease. We assessed the effects of bird food availability on house finch populations using data from the National Survey on Fishing, Hunting, and Wildlife-associated Recreation and the Christmas Bird Count. House finch densities were positively related to the density of people providing food for birds prior to the spread of mycoplasmal conjunctivitis, suggesting that the availability of bird seed can limit the size of finch populations. Following the disease epidemic, house finch declines were greatest where the density of people feeding birds also fell dramatically. This pattern suggests that bird food could have a positive indirect effect on disease-related mortality. Our findings suggest that the collective actions of individual people have the potential to influence resource availability and population dynamics of wildlife in human-modified landscapes.
... • Feeder density predicts regional HOFI density (Fischer and Miller, 2015); and ...
... • Consistent with a positive effect of feeding on Mg impacts, the steepest HOFI declines following Mg spread occurred where the number of people feeding birds fell dramatically (Fischer and Miller, 2015). • Symptomatic birds associate with smaller flock sizes and more likely to feed alone, potentially indicating behavioral avoidance (Hawley et al., 2007a). ...
... For bird feeders, programs such as Project Feederwatch (Cornell Lab of Ornithology, 2016) and eBird (Cornell Lab of Ornithology and National Audubon Society, 2016) can easily allow both researchers and the public to monitor the incidence of avian diseases and remove feeders accordingly. However, removing feeders during an outbreak of mycoplasmosis caused declines in fed house finch populations (Fischer and Miller, 2015), furthering the need for more studies on the effects of feeder removal on population health. On a smaller temporal scale, providing feed on a random, rather than predictable, schedule could prevent large aggregations of animals and exclude dominant individuals or species. ...
... Backyard bird feeding can result in positive effects on some bird species, such as improved overwinter survival (Jansson, Ekman, & von Bromssen, 1981), increased population sizes (e.g. Fischer & Miller, 2015;Fuller, Irvine KN, & Armsworth PR, 2012;Fuller, Warren, Armsworth, Barbosa, & Gaston, 2008) or geographic range expansion (e.g. Greig, Wood, & Bonter, 2017;Job & Bednekoff, 2011). ...
... Indeed, bird feeding has been associated with increased abundance or range expansions for certain bird species (e.g. Fischer & Miller, 2015;Fuller et al., 2008Fuller et al., , 2012Greig et al., 2017). In some cases, supplemental feeding has even been used as a conservation strategy for wild birds (e.g. ...
Backyard bird feeding is one of the most common ways people engage with wildlife in many parts of the world. Given its scale, it can have profound consequences for the ecology of feeder birds and their behaviour. While previous work has primarily explored socio‐demographic factors associated with bird feeding, how observations of nature at backyard feeders (e.g. changes in feeder bird abundance, interaction with natural enemies and weather) influence people's propensity to feed birds remain largely unknown.
We examined the association between peoples’ observations at their backyard feeders and their emotions and behaviours related to providing food to birds. We conducted an online survey of a subset of United States participants in Project FeederWatch, a large‐scale citizen science project.
Overwhelmingly, respondents (n = 1,176) reported taking actions, such as managing predators or maintaining feeders, in response to observable natural factors (e.g. increased incidence of disease, the presence of predators, increased bird abundance). Additionally, respondents described a variety of emotional responses to the scenarios of depredation or disease at their feeders, some of which (particularly anger) had a small association with whether a respondent would take action in response. Respondents generally believed that their bird feeding benefits backyard birds (e.g. by improving overwinter survival and overall health), and indicated that natural factors (e.g. bird abundance, disease prevalence) and abiotic factors (i.e. cold temperature) had more of an influence on how much they feed birds than internal constraints such as time and money.
These findings suggest that human behaviour with respect to bird feeding is coupled to observations of nature, which could lead to feedbacks between provisioning intensity and ecological dynamics. Overall, our results have important implications for bird conservation and for understanding the potential benefits that humans receive from provisioning birds.
A plain language summary is available for this article.
... It then spread from poultry to house finches after the latter were introduced to eastern North America by humans. Moreover, the high densities of house finch populations were maintained by bird feeders [17], which then also served as avenues of disease transmission [16]. Overall, humans clearly set the stage for the emergence of this infectious disease, an event that was then followed by very rapid evolution of both host and pathogen. ...
... Figure 1. Mycoplasma gallisepticum infection of house finches is partly supported by high densities of finches maintained by bird feeders [17]. These bird feeders also facilitate parasite transmission [16]. ...
Humans have contributed to the increased frequency and severity of emerging infectious diseases, which pose a significant threat to wild and domestic species, as well as human health. This review examines major pathways by which humans influence parasitism by altering (co)evolutionary interactions between hosts and parasites on ecological timescales. There is still much to learn about these interactions, but a few well-studied cases show that humans influence disease emergence every step of the way. Human actions significantly increase dispersal of host, parasite and vector species, enabling greater frequency of infection in naive host populations and host switches. Very dense host populations resulting from urbanization and agriculture can drive the evolution of more virulent parasites and, in some cases, more resistant host populations. Human activities that reduce host genetic diversity or impose abiotic stress can impair the ability of hosts to adapt to disease threats. Further, evolutionary responses of hosts and parasites can thwart disease management and biocontrol efforts. Finally, in rare cases, humans influence evolution by eradicating an infectious disease. If we hope to fully understand the factors driving disease emergence and potentially control these epidemics we must consider the widespread influence of humans on host and parasite evolutionary trajectories.
This article is part of the themed issue ‘Human influences on evolution, and the ecological and societal consequences’.
... Nestling bird growth and development are influenced by the composition and quality of food given (Orłowski et al., 2015). Therefore, the understanding of population dynamics requires an understanding of the patterns of food supply to nestlings and the factors that influence them (Fischer & Miller, 2015). Although nest predation is likely to be the most important factor affecting the reproductive success of most birds (Rao et al., 2023), parental care can also be an essential factor, which is sometimes overlooked. ...
The house-farmed edible-nest swiftlet ( Aerodramus sp.) is monogamous, produces nests from hardened saliva, and uses echolocation to navigate in the darkness. Most previous studies have focused on swiftlet nest building and incubation behaviour, but nestling provisioning behaviour, crucial for the survival of offspring during the breeding season, remains unclear. This study examined the nestling provisioning behaviour of house-farmed swiftlets at a swiftlet house farm in central Peninsular Malaysia. Complete focal video footage of the provisioning phase of swiftlets was analysed in detail. The overall feeding period decreased as the chick grew older. The parents alternately visited their nest 6-14 times a day from dawn to dusk to feed the nestling. The peak of this activity was from 07:00 to 08:00 and between 19:00 and 20:00. Nestling provisioning behaviour differed between pairs. The egg-laying interval of parents with two chicks was longer and affected the development of the second chick since the first chick more successfully competed for food and grew larger in size. Most second chicks with a smaller body size did not survive, because of being either purposely or unintentionally eliminated by the parents or sibling. The smaller-sized second chicks that survived took a longer time to fledge than the first chick; therefore, parents had to increase their foraging effort to ensure the survival of their chick until fledging. These behaviours may be influenced by physiological factors, such as age, experience, individual fitness, and abiotic factors, such as weather and food resources; therefore, different parental strategies may be established during the nestling provisioning phase.
... its natural fear of humans and pets (Fischer and Miller 2015). A food-conditioned animal is likely to approach other people looking for food (Clark et al. 2015). ...
This study briefly describes the history of synanthropy in a high-altitude bird species , Prunella collaris. A list of food items that synanthropic individuals seek in garbage in the mountains is presented. Possible influences on behavioural changes and physiology of this protected species are discussed. The large number of synanthropic individuals of this species is evidence of how the development of alpine tourism in Europe over the last 200 years has seriously affected the life of alpine fauna.
... While deliberate wild bird feeding is a popular pastime in urban areas around the world, the impact of this human activity on avian communities remains poorly understood. [1][2][3][4][5][6][7] Supplementary food can benefit visiting individuals by mitigating the stress related to food shortage, especially in harsh winters, when a reduction in immunity makes birds more susceptible to disease. [8][9][10] However, there are concerns that supplementary feeding may lead to negative effects on bird health, such as poor body condition or disease outbreaks. ...
Garden bird sugar water feeding is increasingly popular worldwide, but little is known about its effects on bird health and associated diseases. There is a concern that feeding stations can accumulate pathogens and facilitate pathogen transmission between individuals, resulting in adverse effects on body condition of visiting birds. We tested the effects of sugar water feeding in urban New Zealand backyards by sampling target species for multiple infections and comparing bird body condition. For this, we compared backyards with and without sugar water feeders and again compared existing sugar water feeders with various sugar concentrations in two cities and in two seasons. Birds caught in gardens with sugar water feeders had poorer body condition; however, birds had better body condition in the city with the warmer climate (Auckland), during summer, and in gardens with high (≥20%) sugar concentration in sugar water feeders in winter. All screening tests for Chlamydia psittaci and Salmonella spp. returned negative results. Avian poxvirus prevalence in tauhou ( Zosterops lateralis) was four times higher in the city with a warmer climate. The likelihood of lice infection in tauhou was lower in gardens with feeders, in the warmer city, in summer, and at feeders with higher sugar concentrations. In tūī ( Prosthemadera novaeseelandiae), the likelihood of lice infection decreased with an increase in sugar concentration. Coccidia infection was 4.25 times higher in tauhou in gardens with feeders. Despite the identified risks associated with sugar water feeding, there appear to be potential benefits for native nectarivorous birds, specifically in winter.
... Positive effects of deliberate feeding for individual birds are as follows: reduced time needed for foraging, improved body condition and increased reproductive output (Chamberlain et al., 2009;Robb, McDonald, Chamberlain, & Bearshop, 2008). However, negative effects of exploiting anthropologic food are also possible: increased disease transmission (Fischer & Miller, 2015;Pennycott et al., 2007), dependence on the supplementary food resource (Lahti, Orell, Rytkönen, & Koivula, 1998), malnutrition (Ishigame, Baxter, & Lisle, 2006), and increased nitrogen and phosphate load in the water (Hermsen et al., 2011). This negative effect on water ecology will also affect bird health. ...
Supplementary feeding can affect populations of birds. It reduces energy spent on foraging and reduces the risk of starvation, but it also increases the risk of disease transmission and predation. Supplementary feeding may reduce species richness if some species are better able to exploit supplementary food resources than others. Feeding may also artificially inflate the carrying capacity of the ecosystem, leading to bird nuisance in the form of droppings and noise. The aim of this study was to characterise and quantify the risk factors and consequences of feeding free-living birds in public areas in the western part of the city of Amsterdam. In seven study areas, the following data were collected: bird population size and species composition, feeding events, and the type and amount of supplementary food offered. Estimations were made of the nutritional energy provided and the number of birds that could be supported by the food offered. Members of the public who fed the birds were invited to complete a questionnaire on various aspects of feeding. Results showed that supplementary feeding attracts juvenile gulls and feral pigeons, which could in the long-term affect biodiversity. Bread was the main category of supplementary food being offered (estimated to be 67% of the total amount of food). The majority of respondents fed birds so as not to waste bread and meal leftovers. In six of the seven areas studied, an overabundance of nutritional energy was calculated. We conclude that the current type and extent of supplementary feeding in the city of Amsterdam is nutritionally unbalanced and affects species diversity at a local level. The overabundance is undesirable for reasons of both animal health, because it can lead to malnutrition, and public health, because surplus food attracts rats and may also have a negative effect on water quality.
... House Finches are common backyard songbirds that are largely dependent on bird feeders throughout their introduced range in eastern North America (Badyaev et al. 2020). In fact, House Finch densities in the introduced range are positively associated with human population density and the presence of bird feeders (Mertz and Brittingham 2000;Fischer and Miller 2015). Bird feeders are also known to play an important role in the spread of Mycoplasma gallisepticum (MG), a common bacterial pathogen of House Finches (Dhondt et al. 2007a;Adelman et al. 2015). ...
Provisioning of wildlife, such as backyard bird feeding, can alter animal behavior and ecology in diverse ways. For species that are highly dependent on supplemental resources, it is critical to understand how variation in the degree of provisioning, as occurs naturally across backyards, alters wildlife behavior and ecology in ways potentially relevant to disease spread. We experimentally manipulated feeder density at suburban sites and tracked local abundance, foraging behaviors, body mass, and movement in House Finches (Haemorhous mexicanus (P.L. Statius Müller, 1776)), the primary host of a pathogen commonly spread at feeders. Sites with high feeder density harbored higher local House Finch abundance, and birds at these sites had longer feeding bouts and total time on feeders relative to sites with low feeder density. House Finches at high-density feeder sites had lower residual body mass despite greater apparent feeder access. Finally, birds first recorded at low-density feeder sites were more likely to move to neighboring high-density feeder sites than vice versa. Because local abundance and time spent on feeders have both been linked with disease risk in this species, the effects of heterogeneity in bird feeder density on these traits may have important consequences for disease dynamics in this system and more broadly.
... living house finches (Mertz and Brittingham 2000), alter contact rates among house finches (Moyers et al. 2018b), and promote contaminated feeder surfaces (Adelman et al. 2015). These changes have consequences for transmission and infection rates of the bacterium Mycoplasma gallisepticum (Adelman et al. 2015;Fischer and Miller 2015). Infection with this pathogen can lead to increased GCs (Lindströ m et al. 2005;Love et al. 2016), decreased roost-site fidelity that may further increase contact rates (Dhondt et al. 2006), and can inhibit antipredator responses (Adelman et al. 2017). ...
Synopsis
Anthropogenic change has well-documented impacts on stress physiology and behavior across diverse taxonomic groups. Within individual organisms, physiological and behavioral traits often covary at proximate and ultimate timescales. In the context of global change, this means that impacts on physiology can have downstream impacts on behavior, and vice versa. Because all organisms interact with members of their own species and other species within their communities, the effects of humans on one organism can impose indirect effects on one or more other organisms, resulting in cascading effects across interaction networks. Human-induced changes in the stress physiology of one species and the downstream impacts on behavior can therefore interact with the physiological and behavioral responses of other organisms to alter emergent ecological phenomena. Here, we highlight three scenarios in which the stress physiology and behavior of individuals on different sides of an ecological relationship are interactively impacted by anthropogenic change. We discuss host–parasite/pathogen dynamics, predator–prey relationships, and beneficial partnerships (mutualisms and cooperation) in this framework, considering cases in which the effect of stressors on each type of network may be attenuated or enhanced by interactive changes in behavior and physiology. These examples shed light on the ways that stressors imposed at the level of one individual can impact ecological relationships to trigger downstream consequences for behavioral and ecological dynamics. Ultimately, changes in stress physiology on one or both sides of an ecological interaction can mediate higher-level population and community changes due in part to their cascading impacts on behavior. This framework may prove useful for anticipating and potentially mitigating previously underappreciated ecological responses to anthropogenic perturbations in a rapidly changing world.
... The positive influences of feeder use on population size reported here are likely to be the product of a combination of improved survival 3,4 , better physiological condition 13,43 and increased productivity 44 among the individuals frequenting feeders. However, negative impacts of supplementary feeding have been widely reported, particularly those associated with increased disease transmission at feeders and the poor nutritional quality of food supplements [45][46][47][48] . Further research is needed to determine whether, and how, these might limit population growth. ...
There is a multi-billion dollar global industry dedicated to feeding wild birds in residential gardens. This extraordinary boost to food resources is almost certainly reshaping entire bird communities, yet the large-scale, long-term impacts on community ecology remain unknown. Here we reveal a 40-year transformation of the bird communities using garden bird feeders in Britain, and provide evidence to suggest how this may have contributed to national-scale population changes. We find that increases in bird diversity at feeders are associated with increasing community evenness, as species previously rarely observed in gardens have increasingly exploited the growing variety of foods on offer over time. Urban areas of Britain are consequently nurturing growing populations of feeder-using bird species, while the populations of species that do not use feeders remain unchanged. Our findings illustrate the on-going, gross impact people can have on bird community structure across large spatial scales.
... Given the scale at which it occurs, purposeful feeding of wild animals has the potential for widespread consequences for natural populations. It is well known that food resources underlie many demographic processes (Fischer & Miller, 2015;, and that populations can increase when natural diets are supplemented with regular, predictable anthropogenic food sources (Oro et al., 2013). Empirical studies have found that supplemental feeding of wild bird populations can alter foraging effort, territoriality, and the phenology of reproductive behaviors (Robb, McDonald, Chamberlain, Reynolds et al., 2008), and supplemental food has also been linked to increases in individual survival (Brittingham & Temple, 1988;Jansson, Ekman, & Bromssen, 1981;Orell, 1989) and improved condition (Desrochers & Turcotte, 2008;Grubb & Cimprich, 1990;Wilcoxen et al., 2015). ...
Purposeful provisioning of food to wild animals is a widespread and growing activity that has the potential to impact populations and communities. Nevertheless, studies assessing use of recreational feeders by free‐living birds during winter are surprisingly rare and largely limited to regions with continental climates characterized by freezing temperatures and snow cover. In contrast, there is little information available regarding bird use of feeders within warmer climates during winter, despite widespread recreational feeding in these areas. In this study, we quantified visitation patterns to bird feeders in a Mediterranean climate to evaluate the relationship between feeder use and several environmental variables known to influence supplemental feeder use in continental climates. We established a network of bird feeders in Corvallis, Oregon, USA, that were filled with black oil sunflower (Helianthus annuus) seeds and equipped with radio frequency identification (RFID) data loggers that recorded >315,000 visits by 70 individual Black‐capped Chickadees (Poecile atricapillus) across a 5‐month period (October 2016–March 2017). We found extensive variation in feeder use, with individuals averaging 1–406 feeder visits/day and using 1–9 of the 21 feeders that were available; individual variability was largely consistent during the course of our study. At the population level, we found that feeder use decreased from the start of our study, and this decline continued through the period when foraging was most limited by daylight, including the winter solstice. In contrast to theoretical predictions and empirical work in continental climates, we found that weather variables did not drive feeder use and that feeder visits peaked at mid‐day and gradually decreased until sunset. Our study indicates that individual‐level differences combined with seasonality to drive feeder use patterns, and we conclude that use of supplemental feeders during winter in Mediterranean climates appears to differ notably from feeder use in continental climates. Intentional recreational feeding can impact bird populations, and nearly all previous studies have been limited to cold regions characterized by freezing temperatures and snow cover. We assessed bird feeder visitation patterns by individually PIT‐tagged songbirds in a Mediterranean climate during winter to examine the relationships between feeder use and environmental characteristics. We found that individual‐level differences combined with seasonality to drive feeder use patterns, and that feeder use patterns in Mediterranean climates appear to differ notably from those observed in continental climates.
... Bird feeders can act as a fomite for various pathogens and lead to transmission of disease from infected to uninfected individuals (Murray et al., 2016;Becker et al., 2015;Bradley and Altizer, 2006). For example, Mycoplasma gallisepticum is able to persist and remain infectious for 12 hours on bird feeder portals (Dhondt et al., 2007, Fischer et al., 2015. Trichomonas gallinae can survive and replicate in moist bird seed for up to 24 -48 hours depending on seed type (McBurney et al., 2017). ...
The impetus for this report was the widespread trichomonosis outbreak in the summer and fall of 2017 that extended through every province from Ontario east to Newfoundland and Labrador (CWHC, unpublished data). This and other bird feeder associated diseases generate a large amount of public interest and concern. The bird feeding public is passionate about bird protection on their properties, and many are avid conservationists. This document summarizes actions that can be taken by the public and resource managers to reduce disease risk.
... Furthermore, results of the SMI and carcass composition analyses showed that urban Black Ducks can maintain a similar body condition to wild Black Ducks through winter, which further suggests that urban habitats may be important to Black Ducks at the northern limit of their wintering range. Emerging research is highlighting the attraction of various bird species to anthropogenic habitats because of food subsidies (e.g., Fischer and Miller 2015;Walker and Marzluff 2015;English et al. 2017), an attraction which northern wintering Black Ducks appear to display. ...
Body condition is commonly used in ecology to assess the physiological health of an organism or population and can be used to predict individual survival or breeding success. Waterfowl have been the focus of much research on body condition, and we studied body condition via carcass composition and using a scaled mass index (SMI) in American Black Ducks (Anas rubripes Brewster, 1902) wintering in coastal, agricultural, and urban areas of Atlantic Canada. Carcass composition varied between sexes and body mass decreased through winter as fat reserves depleted. Carcass composition was compared with American Black Ducks wintering in the United States, and American Black Ducks wintering in Atlantic Canada were structurally smaller yet proportionally fatter than those wintering in the United States, likely as a mechanism to survive Atlantic Canada’s harsher winters. SMI did not differ between coastal, agricultural, or urban American Black Ducks, indicating that despite known differences in the diets of the Black Ducks from these three areas, they can maintain similar body conditions capable of surviving the winter. We show that the SMI is a nondestructive alternative to study body condition in waterfowl. Our research highlights the adaptability and hardiness of American Black Ducks at the northern limit of their winter range.
... As wildlife diseases are often highly seasonal, avoiding feeding during sensitive periods has been suggested as a measure to mitigate spread of diseases associated with population-level declines, such as during the house finch conjunctivitis peak in the autumn months [16]. However, a study using large-scale surveys found that house finch declines following disease emergence were greatest where the density of bird feeding was reduced, which indicates that while supplementary food provision may contribute to pathogen transmission, there might have been some compensatory positive effect countering the level of disease-related mortality [84]. Comparison of these findings with additional studies, focused on alternative infectious diseases with varying case fatality rates, would be useful to further appraise the evidence for beneficial effects of feeding versus detrimental effects of increased transmission opportunities. ...
Provision of supplementary food for wild birds at garden feeding stations is a common, large-scale and year-round practice in multiple countries including Great Britain (GB). While these additional dietary resources can benefit wildlife, there is a concomitant risk of disease transmission, particularly when birds repeatedly congregate in the same place at high densities and through interactions of species that would not normally associate in close proximity. Citizen science schemes recording garden birds are popular and can integrate disease surveillance with population monitoring, offering a unique opportunity to explore inter-relationships between supplementary feeding, disease epidemiology and population dynamics. Here, we present findings from a national surveillance programme in GB and note the dynamism of endemic and emerging diseases over a 25-year period, focusing on protozoal (finch trichomonosis), viral (Paridae pox) and bacterial (passerine salmonellosis) diseases with contrasting modes of transmission. We also examine the occurrence of mycotoxin contamination of food residues in bird feeders, which present both a direct and indirect (though immunosuppression) risk to wild bird health. Our results inform evidence-based mitigation strategies to minimize anthropogenically mediated health hazards, while maintaining the benefits of providing supplementary food for wild birds.
This article is part of the theme issue ‘Anthropogenic resource subsidies and host–parasite dynamics in wildlife’.
... For example, while our study showed a decrease in rates of aggression with an increasing density of feeders, the presence of feeders in the wild (relative to no supplemental food) likely augments host contact rates by providing high-value pointsource resources. Finally, the abundance of free-living house finches is likely linked to garden feeder abundance [42], providing another potential mechanism by which bird feeder density can contribute to the dynamics of Mg transmission [43] that our study with constant group sizes could not address. ...
Anthropogenic food provisioning of wildlife can alter the frequency of contacts among hosts and between hosts and environmental sources of pathogens. Despite the popularity of garden bird feeding, few studies have addressed how feeders influence host contact rates and disease dynamics. We experimentally manipulated feeder density in replicate aviaries containing captive, pathogen-naive, groups of house finches ( Haemorhous mexicanus ) and continuously tracked behaviours at feeders using radio-frequency identification devices. We then inoculated one bird per group with Mycoplasma gallisepticum (Mg), a common bacterial pathogen for which feeders are fomites of transmission, and assessed effects of feeder density on house finch behaviour and pathogen transmission. We found that pathogen transmission was significantly higher in groups with the highest density of bird feeders, despite a significantly lower rate of intraspecific aggressive interactions relative to the low feeder density groups. Conversely, among naive group members that never showed signs of disease, we saw significantly higher concentrations of Mg-specific antibodies in low feeder density groups, suggesting that birds in low feeder density treatments had exposure to subclinical doses of Mg. We discuss ways in which the density of garden bird feeders could play an important role in mediating the intensity of Mg epidemics.
This article is part of the theme issue ‘Anthropogenic resource subsidies and host–parasite dynamics in wildlife'.
... Bird feeders are a powerful means of facilitating humannature interactions to improve human mental health (Cox et al. 2017) and encouraging people's engagement in local and broader conservation issues (Cox and Gaston 2016). However, we show that promotion of bird feeding as a strategy should be tailored to socio-economic status of householders, and acknowledge that there can be negative consequences for birds and bird communities, such as reduced diet quality (Brittingham and Temple 1992;Rollinson et al. 2003), spread of disease (Fischer and Miller 2015), increased risk of local nest predation (Hanmer et al. 2017), bird-window collisions (Kummer and Bayne 2015), and exclusion of other bird species (Galbraith et al. 2015). Impacts on non-avian species may also occur (Orros et al. 2014). ...
Socio-economic status of urban householders explains some of the variation in avian community composition through its impact on vegetation; however, it may also affect the quality of human–nature interactions through its association with bird-feeding practices. We investigated whether socio-economic status-related differences in bird-feeding exacerbate existing inequities in bird-viewing opportunities, particularly for native species. We surveyed 378 households across three high and three low socio-economic status suburbs in Dunedin, New Zealand, and counted birds in those suburbs. A higher proportion of householders in high socio-economic status suburbs provided food appropriate for native species than those from low socio-economic status suburbs. Food provision was not associated with education level, although people who fed birds had a better knowledge of birds’ names. While feeding sugar water increased householders’ chances of seeing native birds in their own garden, all respondents in high socio-economic status suburbs were more likely to see native birds than householders providing sugar water in low socio-economic status suburbs, as numbers of native birds were very low in low socio-economic status areas. Better-informed bird feeding can improve the likelihood that people in low socio-economic status suburbs can encounter, recognise and value native species, and potentially advocate for their conservation, but incentives to improve vegetation volume and cover are more important.
... However, the relative abundances of only crows and cowbirds were positively related to the numbers of bird feeders, and relative abundance did not increase for any predator species in response to experimental supplementation. Although quantifying the amount of supplementary food consumed by our focal predators was outside the scope of our research, others have shown that anthropogenic foods, including birdseed, can have significant effects on the population demography of generalist species (e.g., Robb et al. 2008, Fischer andMiller 2015). Bird feeders attract cowbirds from great distances and support populations to the extent that reducing bird feeding during the breeding season is one management recommendation for decreasing the risk of brood parasitism and nest predation by cowbirds (Coker andCapen 1995, Chace et al. 2003). ...
The abundance of anthropogenic foods in urban areas offers an excellent opportunity to examine the effects of supplementary food on animal communities, but few studies have examined the consequences of these supplements on relationships between predators and prey. We used observational and experimental approaches to investigate how supplementary food (i.e. bird feeders) affected predator abundances and nest survival of American Robins (Turdus migratorius) and Northern Cardinals (Cardinalis cardinalis) in 7 neighborhoods of Columbus, Ohio, USA. From April to August of 2011-2014, we quantified supplementary foods, the relative abundance of 6 common nest predators, and the nest survival of 2 songbirds. In April-August of 2013 and 2014, we supplemented 3 neighborhoods with additional bird feeders, the supplementary food most frequently available to predators. The effects of bird feeders varied among predator and prey species. Bird feeders were positively associated with the relative abundance of American Crows (Corvus brachyrhynchos) and Brown-headed Cowbirds (Molothrus ater). Neighborhoods with at least 15 feeders had on average 2.7×more crows and 3.2×more cowbirds than neighborhoods with 3 or fewer feeders. Relationships among bird feeders, predators, and nest survival were complex. Nest survival of robins declined with increasing numbers of bird feeders only where crows were most frequently detected. In neighborhoods with the most bird feeders and crows, fewer than 1% of robin nests were expected to survive to fledging (i.e. to 28 days), while in neighborhoods with fewer feeders and/or crows, up to 34% of robin nests were expected to successfully fledge young. In contrast, nest survival rates of cardinals were not related to either feeders or predators. Differences between robins and cardinals in vulnerability to specific predators and diet may partially explain the different patterns that we observed. Thus, although bird feeders generally did not promote nest predation, there may be nuanced and species-specific responses that have the potential to affect common breeding birds.
1. Humans have a particularly strong connection with birds, driving the enormous popularity of residential bird feeding in much of the world.
2. We conducted a web search to document US state wildlife management agency responses to two recent avian disease outbreaks, finding that 23 agencies made recommendations to cease feeding wild birds in 2021–2022.
3. The psychological benefits of bird feeding for humans are well-documented but often overlooked in management decisions in response to avian disease outbreaks.
4. Likewise, ecological evidence does not necessarily support ceasing bird feeding to reduce the spread of every avian disease.
5. Ecological and social science need to be applied in tandem to ensure that well-intended guidance to cease feeding of birds does not have unintended consequences.
1. Supplemental food provided to wildlife by human activities can be more abundant and predictable than natural resources, and subsequent changes to wildlife ecology can have profound impacts on host–parasite interactions. Identifying traits of species associated with increases or decreases in infection outcomes with resource provisioning could improve assessments of wildlife most prone to disease risks in changing environments.
2. We conducted a phylogenetic meta-analysis of 342 host–parasite interactions across 56 wildlife species and three broad taxonomic groups of parasites to identify host-level traits that influence whether provisioning is associated with increases or decreases in infection.
3. We predicted that dietary generalists that capitalize on novel food would show greater infection in provisioned habitats owing to population growth and food-borne exposure to contaminants and parasite infectious stages. Similarly, species with fast life histories could experience stronger demographic and immunological benefits from provisioning that affect parasite transmission. We also predicted that wide-ranging and migratory behaviors could increase infection risks with provisioning if concentrated and non-seasonal foods promote dense aggregations that increase exposure to parasites.
4. We found that provisioning increased infection with bacteria, viruses, fungi, and protozoa (i.e., microparasites) most for wide-ranging, dietary generalist host species. Effect sizes for ectoparasites were also highest for host species with large home ranges but were instead lowest for dietary generalists. In contrast, the type of provisioning was a stronger correlate of infection outcomes for helminths than host species traits.
5. Our analysis highlights host traits related to movement and feeding behavior as important determinants of whether species experience greater infection with supplemental feeding. These results could help prioritize monitoring wildlife with particular trait profiles in anthropogenic habitats to reduce infectious disease risks in provisioned populations.
Rapid urbanization has become an area of crucial concern in conservation owing to the radical changes in habitat structure and loss of species engendered by urban and suburban development. Here, we draw on recent mechanistic ecological studies to argue that, in addition to altered habitat structure, three major processes contribute to the patterns of reduced species diversity and elevated abundance of many species in urban environments. These activities, in turn, lead to changes in animal behavior, morphology and genetics, as well as in selection pressures on animals and plants. Thus, the key to understanding urban patterns is to balance studying processes at the individual level with an integrated examination of environmental forces at the ecosystem scale.
Significance
Bird feeding is essentially a massive global supplementary feeding experiment, yet few studies have attempted to explore its ecological effects. In this study we use an in situ experimental approach to investigate the impacts of bird feeding on the structure of local bird assemblages. We present vital evidence that bird feeding contributes to the bird community patterns we observe in urban areas. In particular, the study demonstrates that common feeding practices can encourage higher densities of introduced birds, with potential negative consequences for native birds.
Human activities dramatically change the abundance, diversity, and composition of species. However, little is known about
how the most intense human activity, urbanization, alters food webs and trophic structure in biological communities. Studies
of the Phoenix area, situated amid the Sonoran Desert, reveal some surprising alterations in the control of trophic dynamics.
Species composition is radically altered, and resource subsidies increase and stabilize productivity. Changes in productivity
dampen seasonal and yearly fluctuations in species diversity, elevate abundances, and alter feeding behaviors of some key
urban species. In urban systems—in contrast to the trophic systems in outlying deserts, which are dominated by limiting resources—predation
by birds becomes the dominant force controlling arthropods on plants. Reduced predation risk elevates the abundance of urban
birds and alters their foraging behavior such that they exert increased top-down effects on arthropods. Shifts in control
of food web dynamics are probably common in urban ecosystems, and are influenced by complex human social processes and feedbacks.
The raccoon dog (Nyctereutes procyonoides) is an introduced species in Europe with a continually expanding range. Since the species is capable of affecting local ecosystems and is a vector for a number of severe zoonotic diseases, it is important to understand its food habits. Raccoon dog diet was studied in Estonia by examining the contents of 223 stomach samples collected during the coldest period of the year, August to March, in 2010-2012. The most frequently consumed food categories were anthropogenic plants (e.g. cereals, fruits; FO = 56.1%) and carrion (e.g. carcasses of artiodactyls and carnivores; FO = 48.4%). Carrion was also the only food category that was consumed significantly more frequently by raccoon dogs exhibiting symptoms of sarcoptic mange than by uninfected animals. Small mammals, which represent intermediate hosts for the zoonotic tapeworm Echinococcus multilocularis, were more commonly recorded in samples also containing anthropogenic plants than expected by chance. Comparison of raccoon dog and red fox (Vulpes vulpes) diet in Estonia revealed higher overlap than found elsewhere in Europe, with 'carrion' and 'anthropogenic plants' making up the bulk of both species' diet; however, raccoon dogs were more omnivorous than red foxes. Our results suggest that while the use of most food categories reflects the phenology of natural food sources, 'anthropogenic plants' and 'carrion' provide an essential resource for raccoon dogs during the coldest period of the year, with the latter resource especially important for individuals infected with sarcoptic mange. Since both of these food categories and small mammals are often found at supplementary feeding sites for wild boar (Sus scrofa), this game management practice may facilitate high densities of mesocarnivores and promote the spread of some severe zoonotic diseases, including alveolar echinococcosis, trichinellosis, rabies and sarcoptic mange.
We performed experiments to test if American Goldfinches (Spinus tristis) could be a competent reservoir for Mycoplasma gallisepticum and play a role in the epidemic spread of mycoplasmal conjunctivitis among House Finches (Carpodacus mexicanus) in North America. We infected one of two individuals housed together in a cage and determined if transmission occurred to the second bird. Probability of transmission between an American Goldfinch and a House Finch (in either direction) was similar to that between two House Finches. In a second experiment small groups of birds (6-8) were housed in large aviaries. Two source birds were inoculated with M. gallisepticum, and transmission to the naive birds in the aviary was recorded. Transmission occurred among House Finches, among American Goldfinches, and from House Finches to American Goldfinches. Transmission was more likely between House Finches than among American Goldfinches, and between House Finches and American Goldfinches. We conclude that American Goldfinches are a competent reservoir for Mycoplasma gallisepticum and could have played a role in the spread of the epidemic as they are more migratory than House Finches.
Parasite infections can influence host foraging behavior, movement, or social interactions. House finches (Carpodacus mexicanus) in the US are susceptible to a recently emerged strain of the bacteria, Mycoplasma gallisepticum. Infected birds develop mild to severe conjunctivitis that could affect their foraging or social behavior. We videotaped house finches with and without conjunctivitis at a bird feeding station in Atlanta, GA to determine whether birds with conjunctivitis differed in feeding duration, efficiency, total food intake, or aggressive interactions. We observed 105 house finch feeding bouts (of which 41% were of birds with conjunctivitis). Infected birds spent more time at the feeding station and had smaller average and minimum flock sizes. House finches with conjunctivitis also showed lower feeding efficiency than noninfected birds in terms of seeds obtained per attempt and number of seeds eaten per unit time. However, because of their longer feeding bouts, birds with conjunctivitis consumed similar total numbers of seeds as birds without conjunctivitis. Finally, house finches with conjunctivitis were displaced from feeder perches less frequently than noninfected individuals and 75% of all observed displacement events consisted of an infected bird displacing a noninfected bird. Differences in flock sizes and feeding behavior of birds with and without mycoplasmal conjunctivitis could influence the fitness effects and transmission of this bacterium in wild house finch populations.
When measured by extent and intensity, urbanization is one of the most homogenizing of all major human activities. Cities homogenize the physical environment because they are built to meet the relatively narrow needs of just one species, our own. Also, cities are maintained for centuries in a disequilibrium state from the local natural environment by the importation of vast resources of energy and materials. Consequently, as cities expand across the planet, biological homogenization increases because the same “urban-adaptable” species become increasingly widespread and locally abundant in cities across the planet. As urbanization often produces a local gradient of disturbance, one can also observe a gradient of homogenization. Synanthropic species adapted to intensely modified built habitats at the urban core are “global homogenizers”, found in cities worldwide. However, many suburban and urban fringe habitats are occupied by native species that become regionally widespread. These suburban adapters typically consist of early successional plants and “edge” animal species such as mesopredator mammals, and ground-foraging, omnivorous and frugivorous birds that can utilize gardens, forest fragments and many other habitats available in the suburbs. A basic conservation challenge is that urban biota is often quite diverse and very abundant. The intentional and unintentional importation of species adapted to urban habitats, combined with many food resources imported for human use, often produces local species diversity and abundance that is often equal to or greater than the surrounding landscape. With the important exception of low-income areas, urban human populations often inhabit richly cultivated suburban habitats with a relatively high local floral and faunal diversity and/or abundance without awareness of the global impoverishment caused by urbanization. Equally challenging is that, because so many urban species are immigrants adapting to city habitats, urbanites of all income levels become increasingly disconnected from local indigenous species and their natural ecosystems. Urban conservation should therefore focus on promoting preservation and restoration of local indigenous species.
Host individuals who are infected with a pathogen may alter their behaviour in ways that influence transmission. We observed a marked population of house finches (Carpodacus mexicanus (Muller, 1776)) in Ithaca, New York, to test whether individuals change their behaviour at feeding stations when infected with a prevalent bacterial pathogen, Mycoplasma gallisepticum (MG). We found that house finches with conjunctival lesions consistent with MG infection fed for longer bouts of time than individuals without conjunctivitis. Furthermore, the same individuals that were observed both with and without conjunctivitis during 3years of study were more likely to feed alone and associated in significantly smaller flocks when conjunctivitis signs were present. These results suggest house finches alter their foraging and social behaviour at feeding stations when visibly infected with MG. Since MG transmission is thought to primarily occur at feeders, these changes in host behaviour likely have important consequences for MG transmission dynamics.
Urbanization is recognized as one of the greatest threats to biodiversity throughout the world. However, the vegetation within an urbanized landscape is diverse and includes a variety of native and exotic plant species. This variation allows for testing whether certain landscape designs outperform others in the support of native biodiversity. Residential yards represent a large component of an urban landscape and, if managed collectively for birds and other wildlife, could offset some of the negative effects of urbanization. In addition, many urbanites have their primary interaction with the natural world in their front and back yards. Therefore, ensuring positive wildlife experiences for them is essential in promoting urban biodiversity. At the Central Arizona-Phoenix Long-Term Ecological Research site we tested the efficacy of native landscaping in residential yards in attracting native birds. We also explored the links between socioeconomic factors, landscape designs, and urban gradient measurements with the urban bird communities. A redundancy analysis suggested that native desert bird species increased in abundance in neighborhoods with desert landscaping designs, neighborhoods closer to large desert tracts, and higher-income neighborhoods. Variance partitioning showed that collectively these three sets of environmental variables explained almost 50% of the variation in the urban bird community. Results suggested racial and economic inequities in access to biodiversity, whereby predominantly Hispanic and lower-income neighborhoods had fewer native birds. We also found that residents' satisfaction with bird diversity was positively correlated with actual bird diversity. Our study provides new insights into the relative importance of socioeconomic variables and common urban ecological measurements in explaining urban bird communities. Urban planners can use this information to develop residential landscapes that support the well-being of both birds and people.
Wild bird feeding is one of the most common forms of human-wildlife interactions in the Western world. Originally a practice providing nutritional assistance to over-wintering birds, especially in more northern latitudes, birds throughout the cities of the world are now provided with considerable amounts and a variety of foods year-round. Despite the global nature of the practice, remarkably little is known about the outcomes and implications of what may be seen as a supplementary feeding experiment on a massive scale. Although many claims are made about the benefits of feeding, there are growing concerns about the spread of disease, poor nutrition, risk of dependency and many other important issues. Constructive debate among increasingly vigorous proponents and opponents is currently constrained by a lack of reliable information. Here we argue that bird feeding provides an important, if challenging, opportunity for fundamental research in urban ecology.
The roles of dispersal and population dynamics in determining species' range boundaries recently have received theoretical attention but little empirical work. Here we provide data on survival, reproduction, and movement for a Virginia opossum (Didelphis virginiana) population at a local distributional edge in central Massachusetts (USA). Most juvenile females that apparently exploited anthropogenic resources survived their first winter, whereas those using adjacent natural resources died of starvation. In spring, adult females recolonized natural areas. A life-table model suggests that a population exploiting anthropogenic resources may grow, acting as source to a geographically interlaced sink of opossums using only natural resources, and also providing emigrants for further range expansion to new human-dominated landscapes. In a geographical model, this source-sink dynamic is consistent with the local distribution identified through road-kill surveys. The Virginia opossum's exploitation of human resources likely ameliorates energetically restrictive winters and may explain both their local distribution and their northward expansion in unsuitable natural climatic regimes. Landscape heterogeneity, such as created by urbanization, may result in source-sink dynamics at highly localized scales. Differential fitness and individual dispersal movements within local populations are key to generating regional distributions, and thus species ranges, that exceed expectations.
An ongoing outbreak of conjunctivitis in free-ranging house finches (Carpodacus mexicanus) began in 1994 in the eastern United States. Bacterial organisms identified as Mycoplasma gallisepticum (MG) were isolated from lesions of infected birds. MG was also isolated from a blue jay (Cyanocitta cristata) that contracted conjunctivitis after being housed in a cage previously occupied by house finches with conjunctivitis, and from free-ranging American goldfinches (Carduelis tristis) in North Carolina in 1996. To investigate the molecular epidemiology of this outbreak, we produced DNA fingerprints of MG isolates by random amplification of polymorphic DNA (RAPD). We compared MG isolates from songbirds examined from 1994 through 1996 in 11 states, representing three host species, with vaccine and reference strains and with contemporary MG isolates from commercial poultry. All MG isolates from songbirds had RAPD banding patterns identical to each other but different from other strains and isolates tested. These results indicate that the outbreak of MG in songbirds is caused by the same strain, which suggests a single source; the outbreak is not caused by the vaccine or reference strains analyzed; and MG infection has not been shared between songbirds and commercial poultry.
Observations from a citizen-based survey were used to identify potential risk factors associated with mycoplasmal conjunctivitis (Mycoplasma gallisepticum) in eastern house finches (Carpodacus mexicanus). Between November 1994 and October 1996, 778 volunteers provided 7,224 monthly observations at residential bird feeding sites across an eight state region in the eastern USA. Information collected by questionnaires included health status of house finches and four sympatric passerine species, types and number of bird feeders maintained, neighborhood housing locale and altitude of the observation site. Bivariate analyses revealed that house finches were 14 to 72 times as likely to be observed with conjunctivitis than the sympatric species studied. Year of the study, season, and the presence of platform, hopper, and tube type feeders were significantly associated with conjunctivitis in house finches. Multivariate analysis using a logistic regression model suggests that increased risk of conjunctivitis in house finches was associated with the second year of the study (the third year of the outbreak), the cooler non-breeding periods from September through March, and the presence of tube style feeders. In addition, the presence of raised platform type feeders may have been protective against conjunctivitis in house finches. Prevention of spread of this disease may include modifying bird feeding activities based on season and type of feeder.
In the winter of 1993-94, house finches (Carpodacus mexicanus) with severe conjunctivitis (later shown to be caused by Mycoplasma gallisepticum) were first observed in sub-urban Washington D.C. (USA) and adjacent states. Using a large network of volunteer observers in eastern North America, we were able to track the monthly prevalence of the disease between November 1994 and March 1997. Using the information on 24,864 monthly data forms, we describe the very rapid spread of the conjunctivitis epidemic through the eastern house finch population. The epidemic first expanded mainly north, probably carried along by house finches on their return migration, then mainly toward the southeast, and later west. By March 1997, conjunctivitis had been reported from most of the eastern range of the house finch. The prevalence of the disease seemed to fluctuate seasonally with increases in the fall, probably as a result of dispersing juveniles. House finch numbers decreased throughout winter in areas with cold winters and high conjunctivitis prevalence, suggesting significant mortality associated with the disease.
Although many new diseases have emerged within the past 2 decades [Cohen, M. L. (1998) Brit. Med. Bull. 54, 523-532], attributing low numbers of animal hosts to the existence of even a new pathogen is problematic. This is because very rarely does one have data on host abundance before and after the epizootic as well as detailed descriptions of pathogen prevalence [Dobson, A. P. & Hudson, P. J. (1985) in Ecology of Infectious Diseases in Natural Populations, eds. Grenfell, B. T. & Dobson, A. P. (Cambridge Univ. Press, Cambridge, U.K.), pp. 52-89]. Month by month we tracked the spread of the epizootic of an apparently novel strain of a widespread poultry pathogen, Mycoplasma gallisepticum, through a previously unknown host, the house finch, whose abundance has been monitored over past decades. Here we are able to demonstrate a causal relationship between high disease prevalence and declining house finch abundance throughout the eastern half of North America because the epizootic reached different parts of the house finch range at different times. Three years after the epizootic arrived, house finch abundance stabilized at similar levels, although house finch abundance had been high and stable in some areas but low and rapidly increasing in others. This result, not previously documented in wild populations, is as expected from theory if transmission of the disease was density dependent.
An epidemic of conjunctivitis among house finches (Carpodacus mexicanus) caused by Mycoplasma gallisepticum (MG) bacterial infections was first described in 1994. The disease exhibits high primary host specificity, but has been isolated from a limited number of secondary avian hosts at various times and locations. We used records from the House Finch Disease Survey, a continent-wide, volunteer monitoring project, to document the host range of conjunctivitis in birds at feeding stations and to investigate how disease in house finches might influence the spread of conjunctivitis to other hosts. Between 1994 and 1998, participants recorded 675 cases of conjunctivitis in 31 species other than house finches in eastern North America. Seventy five % of these cases were observed among three species: American goldfinches (Carduelis tristis), purple finches (Carpodacus purpureus) and house sparrows (Passer domesticus). The proportion of sites with diseased wintering populations of the three species increased over the 4 yr study and coincided with range expansion of conjunctivitis in house finches. Sites with diseased house finches present were significantly more likely to report conjunctivitis in each of the three species during the same month. These observations are most consistent with transmission of an infectious agent (presumably MG) from house finches to these secondary hosts via spillover of localized epidemics, rather than sustained interspecific transmission.
Mycoplasma gallisepticum (MG) has caused an endemic upper respiratory and ocular infection in the eastern house finch (Carpodacus mexicanus) after the epidemic first described in 1994. The disease has been studied by a number of investigators at a population level and reports describe experimental infection in group-housed MG-free house finches. Because detailed observation and evaluation of individual birds in group-housed passerines is problematic, we studied individually housed house finches that were experimentally inoculated with the finch strain of MG in a controlled environment. To accomplish this, a study was conducted spanning the period of November 2001-April 2002 with 20 MG-free (confirmed by the rapid plate agglutination assay and polymerase chain reaction [PCR] assay) eastern house finches captured in the Cayuga Basin area of central New York (USA) in the summer of 2001. After a period of acclimatization and observation (12 wk), 20 finches were inoculated with a 0.05-ml aliquot of MG (3.24 x 10(5) colony-forming units/ml) via bilateral conjunctival sac instillations. Two additional finches acted as controls and were inoculated in the same manner with preservative-free sterile saline solution. After inoculation, all finches except the controls exhibited clinical signs of conjunctivitis within 2-6 days. The progression of the disease was evaluated by several methods, including PCR, behavioral observations, and physical examination including eye scoring, body weight, and body condition index. Over a period of 21 wk, MG-infected finches developed signs of disease and recovered (80%), developed signs of disease and progressed to become chronically infected (15%), or died (5%). We hypothesize that the high survival rate and recovery of these finches after infection was associated with the use of controlled environmental conditions, acclimatization, a high plane of nutrition, and low stocking (housing) density, all of which are factors documented to be important in the outcome of MG infections in domestic poultry and other species.
Ever since Mycoplasma gallisepticum emerged among house finches in North America, it has been suggested that bird aggregations at feeders are an important cause of the epidemic of mycoplasmal conjunctivitis because diseased birds could deposit droplets of pathogen onto the feeders and thereby promote indirect transmission by fomites. In this paper we bring the first experimental evidence that such transmission (bird-to-feeder-to-bird) does actually take place. House finches infected via this route, however, developed only mild disease and recovered much more rapidly than birds infected from the same source birds but directly into the conjunctiva. While it is certainly probable that house finch aggregations at artificial feeders enhance pathogen transmission, to some degree transmission of M. gallisepticum by fomites may serve to immunize birds against developing more severe infections. Some such birds develop M. gallisepticum antibodies, providing indication of an immune response, although no direct evidence of protection.
Recreational bird feeding is an extremely popular activity that influences winter bird distribution and demography and may influence other organisms near feeders. In the United States, an estimated 60 million people, or 43% of households, currently feed wild birds. For this reason, it has been suggested that public bird feeding currently is the largest wildlife management activity in northern temperate regions. We used a replicated experiment utilizing mealworms (Tenebrio molitor) as surrogate overwintering arthropods to examine whether supplemental winter bird feeding influences kill rate on nearby alternative foods (i.e., mealworms). After 6 weeks of exposure during winter 2000-2001, more mealworms were consumed in feeder plots than in control plots. Predation intensity on mealworms did not decline at distances up to 20 m from feeders. Our findings support the hypothesis that the aggregation of birds near a feeder results in increased predation on nearby bark-dwelling arthropods. Use of winter bird feeders as a potential alternative form of arthropod pest control deserves further study.
Reports on the frequency with which mortality due to causes other than predation or accidents occurs at feeders, and describes factors that may affect the probability of mortality occurring at feeder sites. -from Authors
Can enhancement of garden habitat for native birds have conservation benefits, or are garden bird assemblages determined by landscape and environmental characteristics? The relative roles of vegetation structure, floristics and other garden attributes, and environmental and landscape controls, on the abundance and richness of bird species in 214 back or front gardens in 10 suburbs of Hobart, Tasmania, Australia, are addressed to answer this question. Birds were counted in each garden and the resources they utilized noted. Vascular plant species and other attributes of the garden were noted, along with rainfall, altitude, distance from natural vegetation, distance from the city and garden size. Garden floristics and bird assemblages were ordinated, and garden groups characterized by particular assemblages of birds identified. General linear modelling was used to determine the combinations of independent variables that best predicted the richness of birds and the abundance of individual bird species and groups of species. The models for bird richness, bird species and groups of bird species were highly individualistic. Although native birds showed a preference for native plants, they also utilized many exotic plants. Exotic birds largely utilized exotic plants. Variation in garden characteristics does substantially affect the nature of garden bird assemblages in Hobart, with weaker environmental and landscape influences. The fact that gardens can be designed and managed to favour particular species and species assemblages gives gardeners a potentially substantial role in the conservation of urban native avifauna.
Every year, millions of households provide huge quantities of supplementary food to wild birds. While alteration of the natural dynamics of food supply represents a major intervention in avian ecology, we have a remarkably limited understanding of the impacts of this widespread pastime. Here, we examine the many and varied responses of birds to supplementary feeding at backyard feeders - in large-scale management projects and in focused academic studies - and evaluate population responses to the bird-feeding phenomenon. Our review encompasses a wide range of species, from songbirds to raptors, and compares provisioning with a variety of foods, at different times of year and in different locations. We consider positive impacts, such as aiding species conservation programs, and negative ones, such as increased risk of disease transmission. It seems highly likely that natural selection is being artificially perturbed, as feeding influences almost every aspect of bird ecology, including reproduction, behavior, demography, and distribution. As the effects of bird feeding cascade through ecosystems and interact with processes of environmental change, we suggest areas for future research and highlight the need for large-scale experiments, with a particular focus on the backyards of an increasingly urban and generous, but sometimes fickle, human population.
Competition is a major force in structuring ecological communities. It acts directly or indirectly, in which case it may be mediated by shared natural enemies and is known as 'apparent competition'. The effects of apparent competition on species coexistence are well known theoretically but have not previously been demonstrated empirically in controlled multigenerational experiments. Here we report on the population dynamic consequences of apparent competition in a laboratory insect system with two host species and a common parasitoid attacking them. We find that whereas the two separate, single host-single parasitoid interactions are persistent, the three-species system with the parasitoid attacking both hosts species (which are not allowed to compete directly) is unstable, and that one of the host species is eliminated from the interaction owing to the effects of apparent competition.
Abstract The absence of small birds from many suburban areas may be due to adverse garden characteristics, interspecific aggression or human behaviour such as supplementary food provisioning that encourages predators. We investigated the relationship between these factors and the presence of seven small bird species in Sydney through a community-based survey. The survey was conducted by participants over a 7-day period between 7 am and 10 am in November and early December 2000. Three dominant species, the noisy miner (Manorina melanocephala), pied currawong (Strepera graculina) and common myna (Acridotheres tristis) were each present in over 59% of gardens. Each small bird species was present in less than 40% of gardens. All small birds were negatively associated with noisy miners, but only the silvereye (Zosterops lateralis) was negatively associated with pied currawongs. None of the species of small birds was negatively associated with common mynas. Four species of small birds were associated with at least one habitat variable, notably the proportion of native vegetation. Although more birds were recorded in gardens in which meat was provided, there were significantly fewer small birds in these gardens. There were also more birds recorded in gardens where seed was provided, with red-browed finches (Neochmia temporalis) positively associated with seed provisioning in most regions of Sydney. The presence of dogs and cats was not related to the total abundance of birds overall or small birds in gardens. While garden characteristics may influence the presence of small birds to some degree, the presence of noisy miners, a species that are thought to aggressively exclude other species from their territories, is likely to be an important influence on these species in suburban areas. Furthermore, supplementary feeding by people is likely to negatively influence some small birds. The presence of carnivorous pets does not seem to influence the presence of small birds at the scale of the individual garden.
Households across the developed world cumulatively spend many millions of dollars annually on feeding garden birds. While beneficial effects on avian assemblages are frequently claimed, the relationships between levels of garden bird feeding and local avian populations are unknown. Using data from a large UK city, we show that both avian species richness and abundance vary across different socioeconomic neighbourhood types. We examined whether patterns in bird feeding could explain this variation. The density of bird feeding stations across the urban environment was strongly positively related to avian abundance, after controlling for differences in habitat availability. This effect was almost exclusively driven by the abundance of those species known to utilize garden feeding stations frequently. In contrast, the density of feeding stations had no effect on avian species richness. We also examined variation in the proportion of households in different communities that provide food for birds, a factor that is not correlated with feeder density. The prevalence of bird feeding across different neighbourhoods declined as socioeconomic deprivation increased, and increased with avian species richness and abundance. Our results suggest that the provision of supplementary food for birds by multiple landowners across a city can impact the status of urban bird populations. The potential for harnessing these actions for conservation needs to be explored.
As urbanisation increases globally and the natural environment becomes increasingly fragmented, the importance of urban green spaces for biodiversity conservation grows. In many countries, private gardens are a major component of urban green space and can provide considerable biodiversity benefits. Gardens and adjacent habitats form interconnected networks and a landscape ecology framework is necessary to understand the relationship between the spatial configuration of garden patches and their constituent biodiversity. A scale-dependent tension is apparent in garden management, whereby the individual garden is much smaller than the unit of management needed to retain viable populations. To overcome this, here we suggest mechanisms for encouraging 'wildlife-friendly' management of collections of gardens across scales from the neighbourhood to the city.
Naturally-occurring mycoplasmal conjunctivitis is described among 104 wild-caught, and initially seronegative, house finches (Carpodacus mexicanus) maintained in captivity for 12 wk during November 1995 through January 1996. Finches housed in three pens were monitored for clinical signs, and > or = 10 birds were euthanatized for necropsy and mycoplasma testing every 2 wk. Within 2 to 4 wk following initial detection of lesions, > 50% of the birds in each of three pens developed a debilitating disease characterized by mild to severe ocular swelling, conjunctivitis, and ocular and nasal discharge. Microscopic lesions in affected finches consisted of mild to severe lymphoplasmacytic inflammation with epithelial and lymphoid hyperplasia in conjunctivae, nasal turbinates, and trachea. Mycoplasma gallisepticum infection was confirmed by culture or polymerase chain reaction (PCR) in all birds with conjunctival lesions and in 43% of birds without lesions. An arbitrary primer PCR was used to confirm M. gallisepticum isolates as identical to a field strain previously associated with house finch conjunctivitis. Most birds (89%) with conjunctivitis developed a concurrent antibody response detectable by serum plate agglutination (SPA) within 2 wk of lesion development. Hemagglutination inhibition (HI) and enzyme-linked immunosorbent assay (ELISA) tests were less sensitive than the SPA test. The clinical severity of this disease and high proportion of affected birds suggests that M. gallisepticum may have a negative impact on free-flying house finch populations.
Fluctuations of bird abundances in the Midwest region of the United States have been attributed to such factors as landscape change, habitat fragmentation, depredation, and supplemental feeding. However, no attempt has been made to estimate the collective role of landowner activities that may influence birds across a landscape. To investigate how landowners might influence birds when the majority (> 90%) of land is privately owned, we surveyed all 1694 private domestic landowners living on three breeding bird survey routes (approximately 120 km) that represent a continuum of rural-to-urban landscapes in Southeastern Michigan from October through December 2000. Our survey was designed to investigate (1) the proportion of landowners involved in bird feeding, providing bird houses, planting or maintaining vegetation for birds, gardening, landscaping, applying fertilizer, and applying pesticides or herbicides; (2) whether differences existed between urban, suburban, and rural landowner activities; and (3) whether landowners that carried out a given activity were sociodemographically different from those who did not. Of the 968 respondents (58.5% response rate), 912 (94%) carried out at least one of the activities on their land and the average landowner carried out 3.7 activities. A total of 65.6% fed birds, 45.7% provided bird houses, 54.6% planted or maintained vegetation for birds, 72.7% gardened, 72.3% landscaped, 49.3% applied fertilizer, and 25.2% applied pesticides or herbicides. Significant differences existed between the landscapes, with rural landowners having more bird houses and applying pesticides or herbicides in greater frequency. Similarly, urban landowners had a greater density of bird feeders and houses, but planted or maintained vegetation in the lowest frequency. Participation in activities varied by demographic factors, such as age, gender, and occupation. Scaling each activity to all landowners, including nonrespondents, across all landscapes indicates that between 14% and 82% of landowners may be engaged in a particular activity, with application of pesticides or herbicides having the least potential involvement (13.9%-55.4%) and gardening having the greatest potential involvement (40.1%-81.6%). Taken collectively, our results indicate that landowners are both intentionally and unintentionally engaged in a wide range of activities that are likely to influence bird populations.
Urbanization as a major cause of biotic homogenization
- McKinney
Worldwide urbanization and its effects on birds
- Marzluff
House finch (Haemorhous mexicanus)
- Badyaev
Energy storage and expenditure
- Brodin