Avian Foraging Theory Methodlogy and Applications (Studies in avian biology)

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Recent volumes have focused on emerging questions in avian disease, the ecology of urban birds, and applications of video surveillance to studies of bird behavior. Studies of arctic shorebirds, boreal forest birds, and northern grouse have contributed to a better understanding of the ecology of birds in sensitive ecosystems. Each volume is guest-edited by a team of volume editors who select and coordinate submissions of manuscripts from contributing authors. All manuscripts undergo rigorous peer review, and acceptance of individual manuscripts is based on scientific merit.

Newsletter Google 4. Help pages. Prothero Michael J. Benton Richard Fortey View All. Go to British Wildlife. Conservation Land Management. Go to Conservation Land Management. In their study of wintering black-capped chickadees in Wisconsin in the US, Brittingham and Temple found that a population supplied with supplementary food for 25 years had an identical survivorship to that of an unfed control population nearby. In Australia, adult Australian magpies continued to provide natural foods to their nestlings even when large supplies of favored foods were readily available O'Leary and Jones, There are numerous other studies from a wide variety of species that strongly suggest that in the vast majority of cases individuals that visit feeders do so in rather a sporadic fashion with the diet comprising mainly natural food sources e.

Nevertheless, the proportion of the diet constituted by food supplements can vary seasonally e. One of the most obvious characteristics of bird feeding is that, unlike natural food sources, food supplements are typically made available regularly, in a surfeit, and in the same location.

This has a consequence of concentrating many birds in one place, often including species that are unlikely to interact when foraging naturally, as they compete closely for access to food. As well as increasing aggressive interactions e. Perhaps the best-studied example is provided by the so-called House Finch Disease, a particularly virulent form of conjunctivitis spread by mycoplasmal bacteria e.

Within a few months of this disease's appearance among house finches Carpodacus mexicanus in the mids near Washington DC in the US it was reported by participants in the Cornell Lab of Ornithology's Project FeederWatch. This citizen science program already had a large and active network of members and, having been informed about the disease outbreak, they were able to provide real-time information on the spread of the epidemic as it moved rapidly through the eastern US Bonney and Dhondt, Within just a few years, the house finch population in the eastern US had declined by a third, partly because of the gregariousness of the species, but especially because of the bacteria's capacity to remain viable on damp feeding structures Adelman et al.

Although there is evidence that access to feeders enabled some infected birds to survive for longer by being able to access food despite being sight-impaired , their tendency to remain for prolonged periods on or near feeders undoubtedly increased the likelihood of infection Adelman et al. No cure or antidote has been developed for this disease and incidents are still reported. A similar disease phenomenon occurred in the UK in — involving a trichomoniasis epidemic among several finch Fringillidae species but primarily impacting European greenfinches Chloris chloris. This species had been one of the chief beneficiaries of the increase in the popularity of bird feeding over the preceding decades, its considerable increase in abundance having been attributed at least in part to its attraction to nyjer seed provided as a food supplement Lawson et al.

A detailed picture of the spatio-temporal dynamics of the disease was only made possible through the network of participants in the British Trust for Ornithology's BTO's Garden BirdWatch citizen science program Robinson et al.

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Population Dynamics of the Mountain Chickadee in Northern California

As for the House Finch Disease outbreak, the role of feeders as sites for disease transmission was called into question for the trichomoniasis outbreak. However, in recent decades this species traditionally found in the countryside, has increasingly become a resident of towns and cities, an unexpected move attributed both to declining food resources in rural areas and the proliferation of seed feeders within urban areas Table 1 ; Lawson et al. Although as yet unconfirmed, this suggests a potential source of cross-species transfer of infection that previously would have been unlikely.

These two disease outbreaks are highlighted mainly because of their scale and impact, but also because of the possible role bird feeding plays in increasing rates of infection in avian populations. Moreover, numerous other diseases may be similarly spread because of the interactions of birds at feeders.

These include salmonellosis and Avian Pox, highlighting the importance of thorough and frequent cleaning of feeders as best practice when feeding birds Lawson et al.

Cornell Lab of Ornithology

Despite the severity of these outbreaks, and the relatively high level of publicity associated with them, relationships between feeders and disease remain remarkably under-studied. In a rare exception, the presence of pathogens was investigated among common garden bird species in New Zealand, comparing individuals frequenting feeders with those that were not Galbraith et al.

In addition, birds using feeders carried greater parasite loads than those that did not, with common blackbirds having more helminths and house sparrows more feather lice Phthiraptera Galbraith et al. The importance of food resources in all aspects of the lives of animals is fundamental to understanding population and community dynamics. These complex interactions have been investigated experimentally in a vast number of supplementary feeding studies on many different species and in many biomes.

However, remarkably little empirical data exist for comparison between cities and species. In part, this is due to the many challenges associated with undertaking scientifically robust studies in environments unavoidably occupied by high densities of people. Nonetheless, a growing number of important pioneering investigations are shedding light on the ecological influence of food supplements on the local community of birds. One recent study compared the changes in composition and abundance of the suburban bird community in Auckland, New Zealand over an month period during which food was provided by householders, followed by its withdrawal Galbraith et al.

The results were dramatic for several of the species involved, with increased abundance of house sparrows and spotted doves Streptopelia chinensis —both introduced species—during the provisioning phase, while that of the native gray gerygone Gerygone igata was significantly lower.


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The influence of feeding in shaping avian communities was further emphasized when the community returned to its pre-supplementary feeding structure within only a few weeks of the cessation of feeding. An important but rarely achieved aspect of this study was the willing compliance of the participants to engage with the scientific objectives in stopping feeding birds when instructed to do so to allow the role of feeding to be investigated rigorously.

Although we have claimed that bird feeding is extremely popular and effectively ubiquitous, the timing, duration, and intensity of the practice can be markedly heterogeneous even over short spatial scales. For example, Lepczyk et al. In the UK, Davies et al. In a more detailed investigation within the city of Sheffield in the UK, Fuller et al. This study also found a notably robust positive correlation between the density of feeders and the overall abundance of birds. However, there was no such relationship between feeder density and species richness i.

The remainder of this piece focuses on research priorities that should concern all of us with interests in bird feeding, whether researchers investigating the biological effects of providing food supplements to birds to address targeted research questions, or members of the general public feeding birds over long temporal and wide spatial scales. The world is urbanizing ever more rapidly United Nations, Department of Economic and Social Affairs, Population Division, and as a consequence our interactions with wildlife generally, and birds more specifically, are likely to increase in frequency and, in the case of bird feeding, intensity.

Social networks and culture in birds

That urbanization will inevitably influence all aspects of avian life has not gone unnoticed by ornithologists; research examining how urbanization influences the behavior and ecology of birds has been summarized in a number of books over the last 20 years e. Many provide invaluable accounts of how urbanization and sub-urbanization impacts birds in terms of their behavior, ecology, physiology, abundance, and distribution. The next major challenge, however, is to determine how food availability, especially through the provision of food supplements, influences the biology of birds in our urban centers while contemporaneously being able to control extrinsic factors that influence the biology of urban birds equally strongly e.

In the case of garden bird feeding, we think that it is highly unlikely that the practice will decline in popularity in countries where it is well-established. In fact, there is evidence to suggest that it may intensify as human populations are ever more concentrated in cities in the future where feeder density will inevitably increase Fuller et al.

Therefore, it may be timely to harness further the power of citizen science Dickinson and Bonney, to investigate how feeding influences individual birds, and avian populations and communities in a concerted and structured way. Citizen science has significantly advanced our understanding of various aspects of the breeding biology of birds e. We see no reason why those engaged in bird feeding would not embrace the opportunity to carry out similar projects that improve our understanding of its impacts on urban birds.

Below, we retain the comparative perspectives offered by ongoing research in the Northern and Southern Hemispheres to explain what we consider to be the key future research priorities. Such an approach allows us to compare and contrast the responses to feeding of species between different ecological and avian communities Table 1 , under different seasonal conditions and under different patterns for introduced species as well as native species sometimes in competition for food at feeders.

Here, we pose a number of research questions that will allow us to gain further and new insights into how individuals, populations, and communities respond to bird feeding. Modern field ornithology has access to an increasing number of methodologies that allow this question to be answered effectively. They include, for example, the marking of individual birds with devices such as Passive Integrated Transponder PIT tags that quantify visitation rates to feeders where receivers have been incorporated into feeder access points e.


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However, the number of feeder visits that a bird makes may reflect intense defense of food, and therefore the value that the bird places on this resource, but it may not indicate levels of food consumption. More invasive protocols involving tissue sampling enable methods such as fatty acid signature characterization to be carried out Andersson et al. Such approaches have revealed that there is much variability in dietary intake of food supplements within populations of blue tits visiting feeders in the winter in Northern Ireland Robb et al.

Statistical approaches that allow dietary reconstruction from SIA outputs using Bayesian modeling are growing ever more sophisticated e. These approaches promise much in improving knowledge of urban birds' dependence on food supplements. Examination of the patterns of feeder use by birds exposed to long-term food supplementation and how they relate to over winter-survival, recruitment into the breeding population, investment of energy, time, etc. The challenge will be directly relating dietary composition to reproductive and life-history traits of birds when we know that they are sensitive to so many intrinsic and extrinsic factors.

Both surveys provide invaluable long-term species richness and abundance data over large spatial scales but neither is targeted specifically at urban areas and food availability is not manipulated in the sense that provisioning is not experimentally prescriptive. Manipulative feeding studies have attempted to mimic urban habitats by providing food supplements over long periods from feeders in high density.

One such study Robb et al. Harrison et al. We know that some urban bird species demonstrate reduced clutch size and productivity in urban landscapes Chamberlain et al. This could be achieved through surveys combining monitoring efforts of both feeders and nests.

The challenge will be recruiting sufficient participants to undertake monitoring of both nests and feeder use by breeding birds. Carry-over effects are defined as the outcome of processes experienced by an organism in one season that subsequently influence its performance in the following season. More investigations need to take place within the urban context as a matter of urgency. Of course, it is one thing to examine how protracted feeding of birds influences their breeding performance within one annual cycle; it is quite another to study how food supplementation throughout the life of an urban bird influences its lifetime reproductive success Newton, Examination of whether birds exposed to long-term food supplementation exhibit carry-over effects that result in their improved breeding performance and survival.

The challenge will be controlling for major sources of variation between birds in breeding experience, age, and onset of senescence. Food supplementation is a potent tool in applied conservation of endangered species when it is employed to promote the establishment of new populations in areas that have been ecologically restored e. However, it is not a panacea and in the case of kakapo, as well as promoting recruitment, food supplementation resulted in unpredicted adverse effects such as breeding adult obesity Powlesland and Lloyd, and an unwanted skew toward a male-biased sex ratio in offspring Clout et al.

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In light of the negative as well as the positive effects of intentional feeding of birds outlined above, we feel that it is critical that research be directed urgently toward understanding the impacts of feeding on the mating behaviors of urban birds. Our focus in this context is on the role that feeding plays in connecting bird populations within towns and cities through the movements of individual birds. After all, such connectivity may be of major importance in the processes of natural selection i.

In turn, it has downstream effects on population dynamics, the distribution of species, the spatial distribution of genetic diversity, and urban ecosystem functioning Unfried et al.

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