Vertebrate Conservation
Current projects
URBAN BIRD STUDY: can you help?
Garden birds are perhaps the most familiar wild animals present in our towns and cities, and huge.jpg)
numbers of people gain a great deal of pleasure from feeding them and by providing boxes for them to nest in. Species like blue tits and great tits readily take advantage of our hospitality and appear to be thriving. However, there is some evidence that the urban environment itself, and our feeding practices, could be having a negative effect on the reproductive success of these species (Image of blue tit copyright Mark Fellowes 2012).
Impact of habitat structure
While breeding, blue tits and great tits face the dual problems of finding enough food and then transporting it back to the nest. Even where food is abundant and trees are close together, parent birds have to make dozens of round trips every day. However, as trees become more widely dispersed and / or food becomes less abundant, parent birds either have to work harder or simply deliver less food. For example, Strauss et al. (2005) found no difference in the number of visits to nests by blue tits in good versus poor woodlands, but pairs in poor habitat covered 674 km whilst rearing chicks compared to 375 km in good habitat. Additionally, Tremblay et al. (2005) reported that blue tits in good woodland habitats made approximately 36 visits each hour to their nest compared to just 17 for individuals in poor habitats. All of these effects would be expected to impact the breeding success of individual birds, either by reducing the number of chicks raised or by lowering adult survival rates.
The same processes also seem to be present in some habitats in urban areas. In a comparison of the breeding success of great tits in an urban park versus deciduous woodland, Hinsley et al. (2008) found that pairs in the park had smaller clutch sizes (8.4 versus 9.7) and fledged many fewer chicks too (5.9 versus 8.8). Despite this, birds in the park worked much harder, expending an average of 86 kJ per day compared to 78 kJ per day in the woodland. Overall, parent birds in the park worked about 64% harder for every chick reared because of the wide spacing of trees in the park habitat.
It is plausible that these negative influences are also present within the suburbs of UK towns and cities as most large trees are widely dispersed between residential gardens, or are simply absent. Furthermore, urban tree dispersion is likely to vary in relation to housing density and age. For example, recent housing developments constructed as part of national campaigns to increase the availability of affordable housing tend to have small gardens with few large trees. In comparison, older houses tend to have more mature gardens with large trees, although these are still widely dispersed.
It is important, therefore, to investigate how the breeding success of species such as blue tits and great tits varies between and within different urban areas in the UK.
Providing artificial food
It is currently estimated that people in the UK put out approximately 60,000 tonnes of food for birds annually at a cost of around £270 million (Fuller et al. 2008; Jones & Reynolds 2008). In effect, this is a large-scale supplementary feeding "experiment" that could have repercussions for lots of different species, both positive and negative. For example, Robb et al. (2008) demonstrated that feeding birds over-winter, but stopping before spring, increased the numbers if chicks fledged in the breeding season because the parent birds were in better physical condition.
However, another effect observed in Robb et al.'s (2008) study was that birds laid clutches earlier and chicks fledged earlier too. Although chicks that are fledged earlier can have higher survival rates than those reared later in the year, this could lead to a mismatch, or "decoupling", of the timing of reproduction and peaks of key natural prey availability. For example, it would be predicted that breeding has evolved to occur at a time when prey, such as caterpillars, are widely available to parents feeding chicks and to fledglings once they have left the nest. Therefore, over-winter feeding, earlier lay dates and decoupling may result in have negative impacts, including higher chick mortality.
Furthermore, a more recent study in Worcestershire examining the effects of feeding birds during March-July identified a range of negative effects (Harrison et al. 2010), including a reduction in the clutch size, hatching success and brood size in both blue tits and great tits. This is especially worrying because one of the recent trends in the UK is an increase in feeding spring and summer.
As above, therefore, it is important to investigate how the breeding success of species such as blue tits and great tits varies between and within towns and cities in the UK. And to do this we need your help.
HOW YOU CAN HELP
To investigate how the breeding success of blue tits and great tits varies within urban areas, we are looking to enlist the help of volunteers who have cameras fitted to nest boxes in their garden. This way we hope to be able to extract key information from a wide variety of locations to begin to tackle the issues outlined above.
Therefore, IF YOU HAVE A NEST BOX CAMERA and would be willing to help collect these data, would you please get in touch with Mr Paul Parker (urbanbirds@reading.ac.uk), an MSc student at the University of Reading, who will be using the data as part of a research project for his postgraduate degree. Paul will then be able to give you more detail about the kind of information we would like to collect.
All information will be treated in the strictest confidence.
All data received will be passed to the Nest Recording Scheme run by the British Trust for Ornithology.
References
- Fuller, R.A., Warren, P.H., Armsworth, P.R., Barbosa, O. & Gaston, K.J. (2008) Garden
bird feeding predicts the structure of urban avian assemblages. Diversity &
Distributions, 14, 131-137. - Harrison, T.J.E., Smith, J.A., Martin, G.R., Chamberlain, D.E., Bearhop, S., Robb, G.N.
& Reynolds, S.J. (2010) Does food supplementation really enhance productivity
of breeding birds? Oecologia, 164, 311-320. - Hinsley, S.A., Hill, R.A., Bellamy, P.E., Harrison, N.M., Speakman, J.R., Wilson, A.K.
& Ferns, P.N. (2008) Effects of structural and functional habitat gaps on breeding
woodland birds: working harder for less. Landscape Ecology, 23, 615-626. - Jones, D.N. & Reynolds, S.J. (2008) Feeding birds in our towns and cities: a global
research opportunity. Journal of Avian Biology, 39, 265-271. - Strauss, M.J., Burkhardt, J.F. & Tomiuk, J. (2005) Foraging flight distances as a
measure of parental effort in blue tits Parus caeruleus differ with environmental
conditions. Journal of Avian Biology, 36, 47-56. - Tremblay, I., Thomas, D., Blondel, J., Perret, P. & Lambrechts, M.M. (2005) The effect
of habitat quality on foraging patterns, provisioning rate and nestling growth in
Corsican blue tits Parus caeruleus. Ibis, 147, 17-24.
Reading fox survey
Urban foxes
Urbanization is one of the most important forms of habitat modification undertaken by humans, and typically results in a wide range of practices that are detrimental to native biodiversity. There are some species, however, that positively benefit from the construction of urban environments; one of these is the red fox (Vulpes vulpes).
Foxes are a common sight in towns and cities in Britain, and they are also becoming increasingly common in urban areas in other countries including Australia, France, Japan and the USA. Generally speaking, urban foxes in Britain cause few serious problems, although this is vehemently disputed by some householders. In contrast, urban foxes in other countries pose a much greater problem as they can transmit important diseases and parasitic infections, such as rabies and echinococcosis. Fortunately, both of these are absent from Britain, although the government continues to monitor and prepare contingency plans for their control should they be introduced into this country. Understanding the behaviour and ecology of foxes in urban areas is, therefore, of considerable applied importance.
Red fox social organization
Red foxes also display an interesting pattern of social organisation. In very productive habitats, such as urban areas, foxes frequently live in small groups of up to six or more individuals; indeed foxes reach higher densities in urban areas than in any other habitat. Typically these groups were thought to consist of a dominant monogamous pair that produce a litter of cubs each year and non-dispersing offspring from previous years that do not breed. Within the group, the foxes do not need to hunt co-operatively to catch their food and spend most of their time foraging alone. One obvious question is, therefore, what benefit(s) do these non-breeding subordinate animals gain from being part of a group? In particular, from an evolutionary perspective, it is necessary to identify the means by which each individual within the group maximise its lifetime fitness i.e. how do they maximise the number of genetic descendants they produce?
There are a number of possible ways they may do this. For example, subordinate foxes may help to raise the offspring of their parents by bringing food back to the den or by babysitting the cubs. If this assistance results in more cubs being produced than the dominant pair could raise on their own, this will also increase the fitness of the subordinate animals as they are related to the cubs of their parents (i.e. their brothers and sisters) to the same degree as they would be to their own cubs had they been allowed to breed. Alternatively, dispersing away from their home territory may increase the likelihood that they will be killed and never get to reproduce; staying at home may therefore be the best strategy for becoming a dominant breeding animal in the long-term, even if it means spending a year or two as a non-breeding subordinate group member.
Furthermore, it is not clear whether subordinates are always prevented from breeding as was previously thought. Recent genetic analyses suggests that fox groups are not as monogamous as first thought, and that subordinate animals do sometimes get to breed. Also, it does not always seem to be that the cubs of the dominant female are sired by the dominant male in her group; instead she may mate with males from outside her own group. One repercussion of this extra-pair mating will be to reduce relatedness between subordinate helpers and the cubs of their mother. In turn, this will reduce any genetic benefits to subordinate animals that they may have gained from helping to raise the cubs of the dominant female. Identifying how individuals within this system maximise their fitness is, therefore, complex and will require long-term studies of known individual animals.
Reading fox survey
Developing field projects to study the behaviour, ecology and management of free-ranging wild animals is very difficult. One of the first steps in this process is to determine how many animals are present and where they are located. And this is the aim of the Reading Fox Survey.
Determining the distribution of foxes in urban areas can be difficult because much of the land is privately owned and not accessible. Fortunately, however, much of this land is residential gardens, parkland or commercial land. Any foxes living in these areas are, therefore, likely to be observed by members of the general public. Therefore, I am asking for your assistance in reporting sightings of foxes within Reading to me. In particular, I am interested in information on litters of fox cubs and dead foxes.
Litters of cubs are useful because they provide a rough estimate of the number of fox groups in an area; remember, each social group typically produces only one litter of cubs each year. Cubs are readily visible during May-June as they play in the vicinity of their den, particularly on sunny days. Other signs that you may have cubs nearby include the remains of prey animals, especially birds, and items such as balls, gloves and shoes that the adults bring back to them to play with. Cubs can also be quite noisy during the night as they fight with their litter-mates to establish a dominance hierarchy.
Dead foxes are a potential source of valuable information on a range of topics. The post mortem analysis of carcasses can provide data on e.g. parasites, diet, productivity, age structure and even mating strategies.
How you can help
Please report sightings of litters of cubs and dead foxes within Reading to Dr Phil Baker, either by email ( p.j.baker@reading.ac.uk) or telephone (0118 3784566).
What the cat brought in
Introduction
The introduction of species into new areas beyond their natural geographic range is widely recognised as one of the major threats to global biodiversity. Introduced species can dramatically affect native species in a wide variety of ways, but one of the most obvious ways in which they do so is through predation. The domestic cat (Felis catus) is considered one of the world's worst invasive species, and has been implicated in the decline and demise of a range of native species, particularly on oceanic islands.
Cats show varying degrees of dependence on humans. Pet cats (also known as house cats or inside/outside cats in other countries) are most common; there are an estimated 9 million pet cats in Britain. Pet cats show the highest level of dependency on humans with the vast majority of their food being provided by their owners. However, many are allowed to roam freely during the day and/or night where they may kill other animals, some of which may be eaten. At the other extreme are feral cats. These live completely free of humans and must hunt for all of their food. Semi-feral cats are midway between pet cats and feral cats in terms of their dependency on humans; although they have no owner, they are often fed by humans to a fairly high degree.
Predator-prey interactions
As they are completely reliant on their prey for food, the number of feral cats that can be supported in a given area is closely linked to the availability of their prey. Therefore, if cat numbers become too high, they tend to reduce prey numbers which in turn leads to a decline in cat numbers. There is, therefore, in general terms, a balance between prey availability and feral cat numbers.
This is not the case with pet cats, however. Because pet cats get most of their food from their owners, their numbers are not directly linked to the availability of prey in their environment. As such, the numbers of pet cats can dramatically exceed the natural carrying capacity of the habitat. In these circumstances, pet cats could potentially have a serious detrimental impact on the prey species they kill i.e. a reduction in prey availability will have no long-term effect on cat numbers. This situation is potentially worrying in conservation terms if the animals being killed by pet cats are in decline or threatened. As a result there has been a lot of interest recently in Britain in the possible detrimental impact of free-ranging pet cats on wild bird populations.
However, the situation is by no means clear. The impact of pet cats on a prey population is dependent on a range of factors including: cat density; the number of that species killed by cats; the number of that species dying from other causes; prey density; and prey productivity. In most cases, there is very little quantified information on any of these components. Therefore, it is premature to assume that cats are having a negative effect on prey populations. Indeed it is quite plausible that cats do not have any significant negative effect on bird populations, since we do know that most do not appear to kill any prey at all. Furthermore, it has been suggested that the species living in urban areas that we see today are present because they are able to withstand cat predation.
What the cat brought in survey
It is clear, however, that the situation warrants study and that it would be beneficial to identify whether or not this is a problem that needs addressing and, if so, what would be the most appropriate course of action. This is the aim of the "What the cat brought in" survey.
This study aims to address this problem by enlisting the support of local cat owners to help record the number of prey animals killed by their pet cat(s). Fortunately, cats often deliver prey animals they have killed to their owners, and this is a valuable source of information on the number of different species that are being taken. As the density of prey species varies between different parts of a town or city in relation to e.g. the availability of different habitats, we will be targeting specific areas within Reading to see how predation by cats varies in relation to prey density. The specific aims of the project are:
- To quantify cat density within specific areas within Reading town limits
- To quantify the number of animals of different prey species killed by cats in those areas by asking owners to keep a record of prey animals returned home to them by their pet(s) g
- To compare the numbers killed with estimates of breeding density and productivity in those areas to begin to estimate whether cat predation is a potentially limiting factor for certain prey species
How you can help
The specific areas we will be working in will be surveyed door-to-door to enlist cat owners to help in this study, so if you have not received a questionnaire then you are not in one of our intensive survey areas. However, in addition to the owners in these specific areas, we are keen to enlist the help of other cat owners in the town and in the surrounding areas to also keep a record of the prey animals that their pet cat(s) bring back to them. Enlisting the help of cat owners can be problematic and can lead to sampling biases; therefore, we are keen to enlist the help of owners whose pet cat(s) DO and DO NOT bring prey animals home.
If you would like to take part in this survey, please contact Dr Phil Baker, either by email ( p.j.baker@reading.ac.uk) or telephone (0118 3784566).