Kitabı oku: «Garden Birds»

CHAPTER 1
Gardens and Birds

PRIVATE GARDENS ARE A FEATURE of most of the dwellings found within the UK. A study by Davies et al. (2009), using data from a number of different datasets, put the proportion of households with an associated garden at 87 per cent. The researchers then used this information, alongside figures for mean garden size and the number of households, to calculate the total area of gardens within the UK. The resulting figure, some 432,964 ha, represents an area larger than the county of Suffolk but still an order of magnitude less than the 4.7 million ha of UK land that is under statutory protection.

While such figures underline that gardens only make up a relatively small part of the UK land area, they are the habitat within which many of us engage with birds and other forms of wildlife. This gives them special importance, not least because gardens provide the best opportunities to empower UK citizens with the conservation and research understanding needed to support sustainable planning, lifestyle and land management decisions. Birds are of particular importance in this context because they are one of the most visible, accessible and appreciated components of the wider natural world. If we can understand how they use gardens, and how this use is perceived by the people who have access to those gardens, then we can begin to provide the evidence and messaging needed to support public engagement with the natural world more widely.

FIG 1. Private gardens vary considerably in their size, composition and use, presenting a series of different opportunities for birds. (Mike Toms)

We also need to recognise that gardens come in many different forms; at the simplest level they have tended to be split into those that are urban, suburban or rural in nature, but there is substantial variation within these broad categories. Many gardens fall within urbanised landscapes, so we also need to understand the relationships that exist between gardens and their surroundings. We know, for example, that city-centre gardens are just one form of urban green space and that birds, being mobile, will move between a city’s many different patches of such space. But how important is the spatial arrangement of these different patches or the temporal pattern of feeding resources available within them? Many of the same questions can be asked of those birds using rural gardens, perhaps bordered by arable farmland or woodland plantations. This underlines that gardens should not be viewed in isolation but rather as a part of a wider landscape over which birds may range. In some cases these ranging movements may take birds not just beyond the boundaries of the gardens and often urbanised landscapes within which they sit, but also beyond the borders of countries or even continents.

FIG 2. The Robin is perhaps the most familiar of our ‘garden birds’ but in reality it is a species of woodland edge habitats. (John Harding)

It is for this reason that this book on garden birds starts by looking at the nature of the garden habitat and the garden’s place within a wider landscape context. Inevitably, this will require us to look at urban ecology and the processes that shape the urban environment, and to look into a future where the ongoing process of urbanisation sees an ever-growing number of us living within towns and cities. We will also use this chapter as an opportunity to ask ‘what is a garden bird?’ and to examine the nature of garden bird communities. Are they, for example, just those species that happen to be generally common and widespread across the wider landscape, or is there something special about garden bird species and the communities that they form.

THE URBAN ENVIRONMENT

One of the most shocking statistics relating to the human population is that showing the proportion of the global population now living within urbanised landscapes (see Figure 3); this figure, which passed 50 per cent in 2008, is projected to reach 66 per cent by 2050 (United Nations, 2014). This increase brings with it an associated increase in the amount of land under urban cover. Urbanisation is an ongoing process and considered to be one of the greatest threats facing species and their ecosystems. It is of particular concern because some of the most intensive urban development is projected to occur within key global biodiversity hotspots (Elmqvist et al., 2013). The growth in the numbers of households globally, and within biodiversity hotspot regions in particular, has been more rapid than aggregated human population growth, reflecting that average household size continues to fall. This is relevant because the reduction in average household size is thought to have added 233 million additional households to biodiversity hotspot countries alone between 2000 and 2015 (Liu et al., 2003). It seems all the more important than ever to understand the implications of urbanisation for biodiversity; to some extent this urgency has been recognised by the research community, with increasing numbers of studies helping to unravel how birds and other forms of wildlife make use of the urban environment and revealing what urban expansion means for their wider populations. Urbanisation also has implications for the ways in which the human population interacts with the wider natural world, of which it is a part, so we also need to learn about these relationships and what they mean for both birds and people; this is something that we will explore in Chapter 6.

FIG 3. The proportion of the human population living within urbanised landscapes passed 50% in 2008 and is predicted to reach 66% by 2050. Redrawn from United Nations data.

The process of urbanisation involves the conversion of natural or semi-natural landscapes – the latter including farmed land – into ones that are characterised by high densities of artificial structures and impervious surfaces. Urbanised landscapes contain fragmented and highly disturbed habitats, are occupied by high densities of people and show an elevated availability of certain resources. Associated with the process of urbanisation is the modification of ecological processes, particularly those linked with nutrient cycling and water flow. The density of bird species within such landscapes is best explained by anthropogenic features and is often negatively associated with the amount of urban cover. This underlines the importance of urban green space, especially gardens and (for some species) urban parks and woodland. Although many bird species decline in abundance once an area has become urbanised, some are able to take advantage of the new opportunities that have been created. Because different species respond to urbanisation in different ways, we typically see a dramatic shift in the structure of avian communities living within urban landscapes and the habitats, like gardens and urban parks, found within them.

Alongside the structural changes seen, which may alter nesting opportunities or the availability of food resources, urbanisation also results in increased levels of disturbance, noise, night-time light and pollution, all of which may impact birds and other wildlife. While some of these impacts may be generally negative across species, there may be instances where such effects are not felt equally. Noise pollution can impact on some species more than others, for example, perhaps because of the frequencies at which such noise tends to occur; bird species whose songs are pitched towards lower frequencies may be affected more than those whose high-pitched songs can still be heard above the background noise. Other species may show a behavioural response, perhaps moving the time at which they sing or even altering the characteristics of the song itself. It has been found, for example, that Robin Erithacus rubecula populations breeding in noisy parts of urban Sheffield sing at night, with the levels of daytime noise experienced by these individuals a better predictor of their nocturnal singing behaviour than levels of night-time light pollution, the latter previously considered to have been the driver for nocturnal song in this species (Fuller et al., 2007a).

Not all of the changes that occur during urbanisation are necessarily negative; the provision of food at garden feeding stations (Chapter 2) is regarded as being generally beneficial, buffering the temporal variation in food availability that is typical of natural landscapes and thought to limit populations. The availability of anthropogenic food, either at garden feeding stations or present as food scraps, is thought to be one of the main factors driving the structure of urban bird communities, something to which we will return shortly. A number of studies have found that urbanisation stabilises both the richness and composition of bird communities, perhaps because there is greater predictability of, and less variation within, the climate and resource availability of more urbanised landscapes (Suhonen et al., 2009; Leveau & Leveau, 2012).

As we’ll also discover later in this chapter, some species are better able to cope with or respond to the impacts and opportunities of the built environment than others, and there are particular traits within bird families or species groups which may lead to them being more likely to adapt to the urban environment (Blair, 1996). This raises the question of just what is a garden bird.

WHAT IS A GARDEN BIRD?

Some people take the term ‘garden bird’ to mean a species that is common and widespread, adaptable and found just as commonly in other habitats. While this is certainly true of many garden birds, it is not true of every species found to use gardens on a regular basis. The phrase ‘common or garden’ – meaning something that is common and consequently of little value – may have also added to the sense that garden birds have little conservation value and are thus of little interest. This may be exacerbated by the sense that gardens themselves are an artificial habitat, highly modified and managed and thus greatly removed from more natural habitats and processes. However, it needs to be remembered that many of the habitats that we consider to form the countryside – such as farmland and woodland – are also often highly managed and very different to wholly natural landscapes untouched by human activities. Once we recognise this, then it becomes possible to accept garden birds less as a distinct type of bird and more as simply a subset of a wider population using a broad range of habitats.

Look at any book on UK garden birds and you will see species that are summer migrants (Swift Apus apus, House Martin Delichon urbicum, Spotted Flycatcher Muscicapa striata), winter visitors (Redwing Turdus iliacus, Waxwing Bomybycilla garrulus, Brambling Fringilla montifringilla, Fieldfare Turdus pilaris), insectivores (Goldcrest Regulus regulus, Wren Troglodytes troglodytes), omnivores (Carrion Crow Corvus corone), cavity nesters (Blue Tit Cyanistes caeruleus, Great Tit Parus major) or have low dispersive ability (House Sparrow Passer domesticus), all underlining the variety of ecological traits encountered within our garden bird community. Certain ecological traits may come to the fore if you look at particular components of the wider community; for example, an examination of the birds using garden feeding stations may suggest the dominance of granivorous and omnivorous species rather than insectivores, a reflection of the types of food being provided (Shochat et al., 2010). A different pattern may be seen in winter from summer, when looking at some aspect of the breeding community, or indeed when looking at the same component (e.g. cavity-nesting) but in different geographical locations. We know, for example, that cavity-nesting species are well represented within the UK garden bird community, having adapted to nest boxes, but are far less common in that of Australia, where native cavity nesters rely on natural tree cavities rather than boxes (Shanahan et al., 2014).

Globally, certain species are well represented within garden bird communities, including Rock Dove/Feral Pigeon Columba livia, House Sparrow and Starling Sturnus vulgaris (Aronson et al., 2014). Also widely represented – at least within the wider urban environment – are introduced or ‘invasive’ species such as Mallard Anas platyrhynchos, Canada Goose Branta canadensis, Collared Dove Streptopelia decaocto and Ring-necked Parakeet Psittacula krameri, plus (in those places beyond their native range) House Sparrow, Starling and Rock Dove/Feral Pigeon. As a group, corvids appear to be well represented, as do pigeons and doves, leading some authors to suggest that urban bird communities globally are becoming more homogenous in their composition (either directly, in terms of particular species, or indirectly, through different species occupying similar ecological niches). This process is something that we will discuss in the next section.

FIG 4. Blackbird is best considered as an ‘urban adopter’, a species that is opportunistic in the way that it uses gardens and the resources that they offer. (John Harding)

The species of birds associated with the urban environment – of which gardens are a key component – can be divided into three main types. These are the ‘urban exploiters’, the ‘urban adopters’ and the ‘urban relicts’. Exploiters are those species, like Feral Pigeon, that are typically abundant within urban areas and which depend upon the anthropogenic resources available within the built environment. Adopters also make use of the resources but are more opportunistic in how they do this, and many of our familiar garden birds can be regarded as being of this kind – think of the Blackbirds Turdus merula and Siskins Spinus spinus that move into gardens during the winter months. Urban relict species are those whose population has managed to hang on within a fragment of their former habitat that is now contained within a wider urbanised landscape; such species tend to be found outside of western Europe, where new cities have emerged quickly within formerly wildlife-rich habitats. Another term that may be encountered when discussing urban bird populations is ‘urban avoiders’, those species that are absent or very poorly represented within the urban bird community.

The Rock Dove/Feral Pigeon is one of the oldest and most cosmopolitan commensal species, whose huge global population reflects early domestication and the subsequent transportation and introduction to sites across the world. The very high Feral Pigeon densities encountered in many cities is, to a large degree, a consequence of supplementary feeding and discarded human food, and the presence of buildings and other structures with an abundance of suitable nest sites. In some cities, such as Singapore, these populations are derived from the rapid expansion of a genetically homogenous group of founder individuals (Tang et al., 2018), underlining how a species can very rapidly colonise an urban area given favourable conditions. Similar patterns may be seen in introduced populations of House Sparrow, Starling and Collared Dove.

The notion that species found in a high proportion of the world’s cities, such as Starling, are successful generalists and able to breed anywhere, does require some refinement. Work by Gwénaëlle Mennechez and Philippe Clergeau has, for example, revealed that while the abundance of breeding Starlings does appear to be similar throughout the urbanisation gradient, the degree of urbanisation still has a measurable negative impact on its breeding success. Working in western France, Mennechez and Clergeau (2006) found that the amount of food delivered to Starling nestlings in more urbanised areas was significantly lower than that delivered elsewhere along the urbanisation gradient, resulting in smaller nestling masses. These urban Starlings were found to produce fewer young, each of seemingly lower quality; while they were able to maintain breeding populations in these highly urban habitats, the species was not as successful as a simple measure of breeding abundance might suggest. This is something to which we will return in Chapter 3.

URBAN BIRD COMMUNITIES

Surprisingly perhaps, one in five of the world’s 10,000 or so bird species is found in the highly urbanised landscapes of major cities, including 36 species that have been identified by the IUCN global Red List as threatened with extinction. (Aronson et al., 2014). Globally, the species richness of urban bird communities ranges from 24 species to 368, with a global median of 112.5 species (Aronson et al., 2014). As just noted, a number of studies, typically involving work carried out within a single city, have suggested that the process of urbanisation results in urban bird communities that are becoming increasingly similar over time, and dominated by a few key species. This process is known as homogenisation and is thought to come about because urbanisation not only extirpates native species from an area but also promotes the establishment of non-native species capable of adapting to the new conditions (Luck & Smallbone, 2010). Although these new conditions tend to be similar in cities across the world, they do not in themselves promote the same species winners; instead, it is our preference for certain species (transporting them to new settlements) that has resulted in the homogenisation seen at a global scale (McKinney, 2006).

In their review of the bird communities of 54 cities, spread over 36 countries and 6 continents, Aronson et al. (2014) found that cities tended to retain similar compositional patterns within their distinct biogeographic regions. While certain non-native species were shared across many of the cities studied, the urban communities had not yet become taxonomically homogenised at a global scale – they retained the characteristics of their local region pool. Four species were found in more than 80 per cent of the cities examined; these being the familiar Feral Pigeon, House Sparrow, Starling and Barn Swallow Hirundo rustica. With the exception of Australasia, the proportion of non-native species found within each urban community was similar (at 3 per cent), Australasia being somewhat higher because of the large number of non-native species introduced into New Zealand by settlers. Work within Europe (Jokimäki & Kaisanlahti-Jokimäki, 2003; Clergeau et al., 2006) suggests that urbanisation here might bring about homogenisation by decreasing the abundance of ground-nesting species and those preferring bush-shrub habitats, but also noting that it is difficult to generalise because of the effects of latitude and diversity in the urban habitats studied.

DISEASE AND THE URBAN ENVIRONMENT

Chapter 4 explores the diseases affecting garden birds in detail, but it is important to give a brief overview here of how disease risks differ between urban and rural environments. Comparisons between the diseases of urban and rural populations of birds have yielded mixed results when it comes to seeking general patterns of occurrence and prevalence. Some studies, such as the work of Grégoire et al. (2002), Fokidis et al. (2008) and Evans et al. (2009a), have found reduced parasite loads in urban populations of garden bird species, including Blackbird. Others, such as Giraudeau et al. (2014) have found higher levels of disease in more urban areas. Giraudeau’s work revealed that the severity of coccidian infection in House Finch Haemorhous mexicanus and the prevalence of pox virus were both inversely related to the proportion of undisturbed habitat within the Phoenix metropolitan area. Patterns of disease infection along urban to rural gradients, and across the different habitats within the urban environment, may differ between diseases, in part a reflection of variation in how different diseases are transmitted. In the case of parasites, transmission may require an intermediate host that is absent from the urban environment (Sitko & Zales´ny, 2014), but for other diseases – including those transmitted between individuals through contaminated food – transmission rates may increase in gardens and other urban sites because of the high densities of birds attracted to garden feeding stations (Lawson et al., 2018). The provision of food at garden feeding stations may also influence disease dynamics (Galbraith et al., 2017a).

FIG 10. Garden feeding stations have been implicated in the transmission of disease between different species of garden bird, but the presence of supplementary food also has positive benefits for birds like this Brambling. (Jill Pakenham)

ARE GARDENS IMPORTANT?

As the figures presented within this chapter demonstrate, gardens and the wider built environment support significant proportions of the breeding populations of certain bird species. In addition, gardens and their associated resources may be important for particular birds at other times of the year or during periods when the availability of key resources within the wider environment is at a seasonal low. This underlines that gardens are important, and not just for species flagged as being of conservation concern. How we manage our gardens and the resources they contain has consequences for bird populations and, as we shall see later in this book, may also help to drive evolutionary change. It is important to remember that garden bird populations do not exist in isolation, since birds are well able to move between different habitats or regions. While gardens may not be as suitable as certain other habitats for breeding, they may be better in other ways, at least for some species.

We are, however, far from fully understanding the role that gardens play in a wider context, particularly in relation to source-sink dynamics, and it is certainly too early to be able to quantify the true value (or cost) of garden living for bird populations here in the UK, in Europe or North America, let alone elsewhere in the world. The mobility of birds makes it difficult to follow individuals throughout their full life cycle; in turn, this prevents us from being able to determine why particular individuals use gardens and the consequences or benefits of this use on future events in their lives. For a young Great Tit, raised in a piece of mature deciduous woodland bordering a city’s suburbs, the presence of suitable food in garden bird feeders may enable it to survive its first winter when it would otherwise have died. While this fortunate individual may fail to secure a prime woodland breeding territory the following year, and instead end up making a failed breeding attempt in a garden setting, it may still have the opportunity to occupy a woodland territory in a subsequent year. In the end, this individual’s lifetime reproductive success may still be better for having used a garden and its resources, than would have been the case had it only ever lived within a woodland site.

FIG 11. Gardens across the globe vary greatly in their structure and in the plants they contain, something that can reflect both cultural differences and local conditions. (Mike Toms)

CONCLUDING REMARKS

Before we leave this chapter and turn to look in more detail at particular aspects of the garden environment, it is worth reminding ourselves that the gardens present here in the UK, and across much of western Europe and North America, are often very different from those in other parts of the world. Thinking about gardens in a more global context forces you to move away from the predominantly recreational basis to gardens located within western Europe and North America. Many home gardens elsewhere are very different and provide families with space to engage in food production for subsistence or small-scale marketing. Such gardens may also play an important social or cultural role, perhaps acting as spaces within which knowledge related to agricultural practices can be shared. The management of these spaces creates structures and microclimates that are typically very different from the surrounding countryside; in this respect they can be considered alongside the more familiar urban and suburban gardens of western Europe, even though they look and act very differently (Guarino & Hoogendijk, 2004). It is known, for example, that ‘home gardens’ support high levels of inter- and intra-specific plant diversity, making them important in a global context, but far less is known about the role that they play for wider biodiversity and, in the context of this book, wild birds (Galluzzi et al., 2010). For the most part, however, we will just consider the gardens of western Europe, North America and Australasia in this book, something that also reflects where the greater amount of research has been carried out. The pattern of research worldwide isn’t just linked to particular geographic areas, since it has also been demonstrated that there is a positive and significant association between the degree of urbanisation of a species and how frequently it has been the subject of scientific study (Ibáñez-Álamo et al., 2017).

This chapter has highlighted the fact that gardens come in many different forms and that this has consequences for the communities of birds associated with them. The birds present in our gardens are the species that have, for the most part, adapted to the process of urbanisation to take advantage of the resources and other opportunities that gardens and the wider built environment provide. While some of these species populations are resident within the built environment, others make use of our gardens on a seasonal basis. Most UK gardens are located within highly urbanised landscapes; with urban land cover globally predicted to triple between 2000 and 2030 (United Nations, 2014), we can expect to see future changes in our garden bird communities. Such changes are part of an ongoing process that has altered the distribution of bird species, changed the composition of avian communities, brought about local extinctions and altered behaviour. It is these features and processes that we will examine of the following chapters, starting with feeding opportunities (Chapter 2), then moving on to an examination of breeding behaviour (Chapter 3), disease risk (Chapter 4) and behaviour (Chapter 5).

CHAPTER 2
Foods and Feeding

FEEDING WILD BIRDS IS UNDOUBTEDLY a popular pastime here in the UK and a great many of us put out mixed seed, sunflower hearts and fat- or suet-based products for our garden birds. The addition of such food to the environment represents a substantial supplementation of the resources available to wild birds, yet we still lack a clear understanding of its effects. In a wider research context, we know that food supplementation can increase survival rates (Brittingham & Temple, 1988a), change community and population structure (Galbraith et al., 2017b), alter behaviour (Saggese et al., 2011; Plummer et al., 2015) and impact on wider biodiversity (Orros et al., 2015a). It has also been linked to disease transmission in birds (Lawson et al., 2018) and to health and well-being benefits in people.

Through this chapter we will explore how and why supplementary food is provided to garden birds, how provision varies across countries, cities and cultures, and the consequences that such provision has for the birds that visit our gardens to partake of this significant resource. Understanding why people feed wild birds and the extent to which they appreciate its costs and benefits will be central to our exploration, as will a review of the scale of food provisioning, which is where we will start this chapter.

THE PROVISION OF FOOD FOR WILD BIRDS

It has been estimated that between one-quarter and two-thirds of households across major parts of Europe, North America, Australia and New Zealand provide food for wild birds (Thomas, 2000; Ishigame & Baxter, 2007; United States Fish & Wildlife Service, 2011; Davies et al., 2012). Within the UK, and using figures from the English Housing Survey and other studies, Davies et al. (2009) reported that 48 per cent of households, and 51 per cent of households with a garden, participated in feeding wild birds. Perhaps more interestingly, the study also reported that 28 per cent of households, and 23 per cent of households with a garden, specifically used bird feeders. An earlier and often quoted study by Cowie & Hinsley (1988a) put the figure at 75 per cent, but was based on a small sample of households (in Cardiff) and did not properly account for those questionnaires that were not returned. Work in Reading, Berkshire, using a face-to-face questionnaire approach outside supermarkets, came up with a figure of 55.3 per cent for the proportion feeding wild birds, of which 65 per cent reported that they fed all year round (Orros & Fellowes, 2015b). Marketing work by the RSPB, using two separate telephone surveys of randomly selected groups of 1,000 people and carried out in summer and winter 2004, indicated that 56 to 61 per cent per cent of people over the age of 16 had fed their garden birds during the past year (RSPB, unpublished).

FIG 12. Suet-based foods, such as fat balls, have become very popular with UK householders, their use targeted at small garden birds like tits and Starlings. (John Harding)

A rough calculation by Zoe Davies and colleagues, based on the population sizes of birds known to use seed feeders, suggests that there is at least one bird feeder for every nine potentially feeder-using birds. This does not allow for the fact that many households provide food in more than one feeder, or that many bird feeders are sitting empty at any one point in time. RSPB data, again from their marketing survey, suggest that on a typical summer’s day one in every seven gardens has at least one empty bird feeder. Even so, it does underline the potential scale of food provisioning taking place within the UK – something Davies et al. (2009) have suggested could equate to a standing crop of 2,580 tonnes of bird food. Figures from the Pet Food Manufacturers Association put UK bird food sales at c. 150,000 tonnes annually, representative of an annual consumer spend in excess of £200 million. O’Leary & Jones (2006) suggest that in excess of 500,000 tonnes of food is provided annually across the UK and US combined, while United Nation’s figures from 2005 put the global bird food industry’s value at $5–6 billion, with growth of c. 4 per cent annually since the 1980s (Lin, 2005).

Thanks to the periodic National Survey of Fishing, Hunting, and Wildlife-Associated Recreation, we know that expenditure on wild bird foods within the United States has doubled over a 20-year period, exceeding $4 billion per year by 2011 (United States Fish & Wildlife Service, 1991; 2011). We lack a comparable survey within the UK, and securing commercially sensitive sales information from the wild bird care sector is problematic, but it is thought that the current annual UK spend on wild bird care products (food, feeders and nest boxes) is between £220 million and £500 million (Fuller et al., 2012).

FIG 13. The proportion of BTO Garden BirdWatch participants presenting different foodstuffs at their garden feeding stations each week across four of the project years (2014–17). Note the increase in fat and suet provision during the winter months. ‘Live’ foods include dried mealworms. Data reproduced with permission from BTO.

Information from the weekly submissions made by BTO Garden BirdWatchers provides a measure of the change seen in different types of bird food (see Figure 13) but these data come from a subset of the national population (see Chapter 6) and do not reveal the actual quantities provided. Having said this, as part of BTO’s work on microevolution in Blackcaps (see later in this chapter), we were able to estimate that the total volume of sunflower hearts and fat products provided by BTO Garden BirdWatchers during the winter months more than doubled from 6.35 tonnes to 17.26 tonnes over the course of a 12-year period (Plummer et al., 2015).

WHY DO PEOPLE FEED WILD BIRDS?

While bird feeding is clearly influenced by external factors, such as socioeconomic status and having access to a garden, it is also shaped by intrinsic and motivational factors. At its heart, bird feeding may be seen as a humane act, an act of kindness reflecting a wish to help a fellow creature. However, this act may be further shaped by other motivations, such as guilt or a wish to learn. Despite the obvious commercial advantages to be gained by understanding motivations for feeding wild birds, there has been relatively little work in this area and many of our assumptions about why people provide supplementary food for wild birds remain untested (Jones & Reynolds, 2008). Understanding motivations requires a considered and rigorously scientific approach; it is all too easy to inadvertently bias a response from a study subject by asking a question in the wrong way.

The work that has been done suggests that people feed wild birds for a range of different reasons driven by underlying environmental, cultural and philosophical perceptions (Davies et al., 2012). Many people derive pleasure from feeding wild birds and in many instances the provision of food is simply a reflection of this. Others feed because they are concerned about wild birds (and other creatures) and wish to nurture and support them. Some provide food because of the experiential knowledge that is gained, while others seek to counter the guilt that they feel over wider human impacts on the environment.

Examination of a random sample of 1,000 participants in BTO’s weekly Garden BirdWatch scheme (Schreiber, 2010) found that ‘pleasure’, ‘contributing to the survival of wild birds’ and ‘studying behaviour’ were the top three justifications given by respondents for feeding. ‘Responding to environmental degradation’ and ‘teaching children’ were also given as reasons for feeding. Of course, participants in a citizen science scheme like Garden BirdWatch are unlikely to be representative of the wider UK public; they have sufficient interest in garden birds to have become involved in a rigorous monitoring scheme and will have been exposed to articles delivering information and messages on the practices associated with feeding wild birds. At this point it is just worth noting that the provision of supplementary food is sometimes practised for other reasons; conservation practitioners use supplementary food to enhance the survival and reproductive success of endangered species, while others use it to reduce predation pressure by provisioning predators; some use it to bring animals to sites where they can be observed or even hunted.

FIG 14. Peanuts were one of the first foods provided specifically for wild birds visiting UK gardens. Originally presented loose or in net bags, peanuts are now typically provided in mesh feeders, though their use has fallen with the arrival of new high-energy seeds. (Jill Pakenham)

The provision of food at garden feeding stations, and indeed the wider participation in wildlife-friendly gardening, may also be a response to peer pressures or the development of a shared social ideal, or to the opportunities provided by having the time and/or financial resources required. The ‘luxury effect’ noted by Hope et al. (2003), Kinzig et al. (2005) and others, where wealthier neighbourhoods support greater levels of vegetation cover and have a greater richness of vertebrate taxa, may also apply to the provision of food for wild birds. We’ll return to this as we move through the next two sections.

As well as seeking to understand the motivations for feeding, it is also important to understand any concerns that those feeding wild birds may have about the practice. While some individuals may only see feeding as being beneficial – for their own interest or for the welfare of the birds themselves – others may continue to feed even if they have concerns about particular aspects of the practice. The sample of BTO Garden BirdWatch participants just mentioned were also asked whether they had any concerns about feeding and, if so, what these might be. Just under half of the respondents noted that they did have concerns; those highlighted being the risk of disease transmission, the risk of attracting predators, and the risk of attracting unwanted species to the garden.

THE VARIATION IN FOOD PROVISION

Across northern Europe and North America the feeding of wild birds appears to have once been a winter practice, suggesting that food was provided in recognition of the challenging winter conditions being faced by birds. To some extent feeding remains a winter practice; as data from BTO Garden BirdWatch reveal, the proportion of its participants providing supplementary food shows a strong seasonal pattern with increasing provision during the winter months. Up until the 1980s, the prevailing view was that feeding wild birds during the breeding season would lead to adult birds feeding their young on unsuitable foods and perhaps lead to nestlings choking on ‘indigestible foodstuffs such as peanuts’. Despite this, a pronounced move towards feeding year-round was made during the 1980s, when the advice provided by both the RSPB and BTO switched from winter only to feeding throughout the year.

The switch in BTO’s position was evidence-based and derived from work carried out by Patrick Thompson, who organised a special spring extension to the BTO’s Garden Bird Feeding Survey (Thompson, 1987). The study sought to compare the numbers of feeding birds in the spring with those seen in winter and to determine which species made use of garden feeding stations during this period. Some 181 participants took part in the winter component, with 113 contributing to the spring extension. While fewer species were recorded in the spring component than in the winter, the same species were present in the top 12 in both studies; for some species the level of feeding in spring was as high as, or higher, than that seen in autumn or winter. In House Sparrow, for example, feeding activity peaked in late spring. Other species, e.g. Robin, Blue Tit and Great Tit, used provided food extensively through into the first month of the spring survey, but after this their use of this resource dropped markedly. This drop in use was thought to reflect a shift towards natural prey, which generally become more abundant in spring. That seed-eating species, like Dunnock Prunella modularis and Greenfinch, did not move away from provided food quite so quickly perhaps underlines a lack of seed availability more widely until later into the year.

The second component of Thompson’s study looked at the breeding season use of supplementary food (peanuts) by Blue Tits and Great Tits across 13 gardens at Ashridge Park, Hertfordshire. This population had been studied by the BTO’s Chris Mead since 1977. Chris was a key figure in the development of several projects studying garden birds. The garden-nesting Blue Tits bred significantly earlier than those breeding in nearby woodland and laid larger clutches. There was no difference in the timing of laying between the two Great Tit populations but the garden-breeding birds laid significantly smaller clutches than their woodland counterparts, and there was no significant difference in the fledging success of either species between the two habitats. The feeding habits of the adult tits were also carefully monitored. While Great Tits were very rarely seen to feed their young on peanuts (less than 7 per cent of visits), the Blue Tits were never seen to do this. Importantly, no young tits were reported to have died from ingesting nuts.

FIG 15. While the food available at garden feeding stations appears to be important to young Blue Tits once they have left the nest, it is only rarely provided to nestlings by adult birds. (John Harding)

Elsewhere, both Cowie & Hinsley (1987) and Perrins (1979) have noted a lower fledging success in tits using gardens compared to woodland habitats, with much of this down to chick starvation, despite the fact that supplementary foods are available in this habitat. This underlines the reluctance of adult tits to feed their young on supplementary food. Collectively, the evidence from Thompson’s study and the wider literature convinced BTO to change its advice on year-round feeding, recognising that the extra food may provide a ‘valuable food source to adult birds’. The advice to switch to year-round feeding in Germany was made even more strongly by Peter Berthold and Gabriele Mohr, both respected researchers, whose book Vögel füttern, aber richtig – loosely translated as ‘feeding birds, but right’ – made a scientifically based case for year-round feeding. Although initially criticised in some scientific circles, the book was well received by birdwatchers, shifting 50,000 copies within two years of first publication. Figures from the UK, taken from the RSPB’s marketing study, suggest that winter and summer feeding levels are now fairly similar, at least in terms of the proportion of people providing food (53 per cent summer and 59 per cent winter).

DIFFERENCES BETWEEN INDIVIDUALS

The suspicion that some people are more likely to put out food for birds than others has proved difficult to test, in a large part because of the methodological difficulties in securing a random and representative sample of respondents when carrying out questionnaire-based studies. The scale at which the data are collected can also cause problems for their interpretation. Fuller et al. (2012), for example, found that three different measures of socioeconomic status – household income, the age of householders and the number of individuals comprising the household – were poor predictors of bird feeding behaviour at the national level; however, all three were found to be strongly related to both the presence of bird feeding and the spatial density of bird feeding stations when they just looked at the city of Sheffield. It appeared that by aggregating data at a wider scale, the researchers had averaged away important fine-scale differences. The Sheffield data revealed that bird feeding and the spatial density of bird feeders increased as household income increased but showed an interesting ‘humped’ relationship with the age and number of householders.

Provisioning may also vary between individuals in terms of how often they put out food, the types of foods they provide and where the food is presented. Roughly a quarter of those interviewed by the RSPB put out food daily, with half putting out food at least once a week, and food was presented roughly equally across bird feeders (33 per cent), bird tables (27 per cent) and on the ground (30 per cent). Davies et al. (2012) found that just 29 per cent of the households they studied provided food at least once a week. The work in Reading, mentioned earlier in this chapter, had a more detailed second component; this looked at a subset of people feeding birds within the city, charting what they provided over a two-year period. As well as the finding that a significantly higher proportion of the individuals feeding year round provisioned daily, compared to those who only fed the birds during autumn and winter, the Reading work also collected valuable information on the amount of food being given. This revealed that each day the median amount provided per garden was 127 g, though ranging from 18 g to 3,573 g. Knowing what food was being provisioned, and in what quantities, enabled Orros and Fellowes to calculate a daily energy value of 628 kcal provisioned per garden per day. In addition to variation in the quantities of food provided, there was also variation in the types of food provided, with 91 per cent of individuals provisioning one to three types of food. Mixed seed was the most commonly provisioned food, by both mass and kcal; interestingly, 43 per cent of individuals still provisioned household scraps.

FIG 16. Various members of the crow family, including Carrion Crow, have taken advantage of the feeding opportunities available at garden feeding stations. Work in North America has highlighted how the nature of these opportunities may vary regionally. (John Harding)

Work in the US has also examined the question of who feeds wild birds, revealing that older people are more likely to provide supplementary food than young people (Lepczyk et al., 2012), and are more likely to be women and to have achieved higher educational qualifications than those not participating (Lepczyk et al., 2004a). Mark Goddard, working on why people in Leeds garden for wildlife, also found that the frequency of bird feeding increased with age (Goddard et al., 2013). The RSPB marketing study, which is probably the study that is most representative of the wider UK population, found that interviewees 35 years of age or older were more likely to feed their birds than those under 35 (RSPB, unpublished). Of course, the characteristics of those provisioning wild birds may sometimes confound attempts to examine the relationships between food provision and other features – for example, housing density (something we touched on in the previous chapter).

REGIONAL DIFFERENCES

Cultural differences in attitudes to birds may explain many of the regional differences in the types and quantities of supplementary food provided for garden birds. The biggest markets for wild bird food and feeding products are based in Europe and North America but even within these regions there are differences between countries and peoples. Within Europe, for example, the feeding of wild birds is common in Germany, Poland, Finland, Switzerland, the UK and the Netherlands, but not in France, Spain or indeed other Mediterranean countries. That cultural differences might be behind the patterns seen within Europe could be suggested by the differing attitudes towards the hunting of small wild birds, still a common practice in the south of Europe but not in the north. Could the differences within Europe also relate to geography and the harsher winter weather encountered further north within the continent?

As Lepczyk et al. (2012) found, some of these regional differences in provisioning practices within North America do indeed relate to climatic conditions. Through a series of parallel studies Christopher Lepczyk and colleagues found that householders in Michigan and Arizona had differing attitudes towards the provision of supplementary food for birds; while 66 per cent of respondents in Michigan provided food, just 43 per cent of those in Arizona did so. The authors put this down to the fact that Michigan is a region that experiences severe winter weather, during which birds face harsher environmental conditions, while Arizona has a more favourable winter climate. In addition, Lepczyk found that Michigan residents were more likely to provide high-quality supplementary foods (such as thistle and sunflower seeds) than those living in Arizona. One further pattern of interest can be seen in in Lepczyk’s study: relatively fewer urban residents engaged in the provision of high-quality food than was the case for non-urban residents; they were, instead, more likely to provide food of a lower quality.

FIG 17. Granivorous (seed-eating) species, like Yellowhammer, dominate at UK garden feeding stations, while insect-eating species tend to be less common. (Jill Pakenham)

Similar findings were reported from Poland, where Tryjanowski et al. (2015) found that urban and rural areas differed in the availability of food, offered intentionally or unintentionally to wild birds during the winter months. Both intentional and unintentional food provision was greater within urban areas than it was in rural locations. While the number of bird feeders and feeding stations differed significantly between the two habitats, the proportion of feeders containing food was similar. Tryjanowkski found differences between the two habitats in the availability of several foodstuffs, with seed feeders and waste food significantly more common in the urban area and animal fat more common at rural sites.

There also clear regional differences in the types of food being provided for wild birds at garden feeding stations in different countries. While the main foods provided at garden feeding stations in the UK and elsewhere in Europe are seed-based, in North American backyards we see the additional use of sugar solution feeders for hummingbirds, and in Australia we see many more high-protein foods provided (such as meat and cheese), reflecting the differing range of species more commonly encountered in Australian backyards.