Managing domestic gardens collectively to promote urban biodiversity

Posted by Lee Dixon

Lee was a Research Masters student in our group before moving to University of Manchester to take up a ‘President Doctoral Scholarship’ to study urban biodiversity. Here he talks about his PhD work. 

Urban biodiversity

Cities frequently consist of a highly diverse mosaic of habitats which are subject to varying degrees of human intervention and manipulation. These habitats range from semi-natural habitats such as urban parks to totally artificial habitats such as industrial parks. As a result, cities have the capacity to hold a large number of ecological niches which in turn can support a surprising number of species. This biodiversity is vital for the sustained provision of ecosystem services, most notably those provided by pollination, but is also important for the health benefits that contact with nature has for humans.

Gardens are important habitat for Bumblebees (Bombus spp) currently declining in Europe and elsewhere as a result of urbanisation and climate change (Photo: Aconcagua).

To maintain high urban biodiversity and associated ecosystem service and health provision, it is important that growth in the world’s cities, land use changes, habitat fragmentation, and other by-products of human living such as pollution, do not result in loss of important species or communities. A key resource for urban wildlife is the domestic garden and their value is at the heart of my PhD. Urban gardens, although individually small in size, cover considerable areas of cities and have the capacity to hold a high level of biodiversity. As a result, domestic gardens taken as a collective entity may reasonably be described as a major nature reserve within cities. However, their value is contingent on the decisions made by householders about the composition of their own garden. 

Greater than 25% of the UK's national population of the Red Listed Song Thrush (Turdus philomelos) are held in domestic gardens (Photo: Tony Mills).

The habitat garden approach

The collective management of domestic gardens whereby multiple domestic gardens are managed in aggregation as a single habitat as opposed to individually (the habitat garden approach) has recently been proposed as a promising means to maintain or boost urban biodiversity. The approach is based on the 'species-area relationship', which describes the typical increase in number of species contained in larger and larger areas.It stands to reason that a collection of gardens all managed sympathetically for wildlife, as a single unit, may be better than individual gardens acting ‘unilaterally’.

South Manchester gardens make up a significant proportion of the urban landscape. Here is Stu's garden and the not-quite-as-nice gardens of his neighbours (Image: Google Maps).

There are, of course, social scientific factors which may influence the level of biodiversity within domestic gardens which are managed collectively as a single habitat. These include differences in how householders perceive the purposes of domestic gardens and different forms of garden wildlife, and the different garden management practices which they may implement in their gardens. These perceptions and management practices, if unfavourable to urban biodiversity, may nullify the potential benefits that this approach may bring to urban biodiversity and, as such, may form a constraining factor in its implementation in residential areas of cities. Moreover, it is unclear how institutions may promote householder perceptions and garden management practices which are favourable to urban biodiversity in order to maximise the potential benefits that the collective management of domestic gardens may bring for urban biodiversity.

'Privatisation' of domestic gardens such as the erection of fences and walls keep gardens relatively small in size and act as barriers to species' movement - in turn reducing the potential benefits that the habitat garden approach may bring to urban biodiversity (Photo: Lee Dixon).

The PhD

This research will explore what effect these householder perceptions and garden management practices may have on the potential benefits that the collective management of domestic gardens may bring for urban biodiversity and, with this taken into consideration, the feasibility of its implementation in cities. The research will also explore what incentives and approaches institutions could employ to promote householder perceptions and garden management practices which are favourable to urban biodiversity, and how these institutions may facilitate householder collaboration in the collective management of domestic gardens.

The specific objectives are

1.    To explore how householders perceive the purposes of domestic gardens, and garden wildlife

2.    To analyse how householder garden management practices may affect the biodiversity of domestic gardens

3.    To explore what incentives and approaches institutions could employ to promote biodiversity favourable householder perceptions and garden management practices

4.    To investigate if the collective management of domestic gardens is an appropriate approach to promoting urban biodiversity

Can hyenas help save mainland Africa’s most imperiled bird?

Posted by Bruktawit Muhamued, Huw Lloyd & Stuart Marsden

Once famed for its highly productive breed of Boran cattle, the Liben Plains of southern Ethiopia are in deep trouble – they are seriously overgrazed by cattle, being encroached by aggressive scrub species, and lost due to conversion to cereal crops. These changes have grave consequences for the livelihoods of the local pastoralists and at the same time have pushed the endemic Liben Lark Heteromirafra archeri to the brink of extinction. The Lark may now represent mainland Africa’s most threatened bird species. 

Liben Lark Heteromirafra archeri. Photo: Paul Donald

The conservation of the Liben Plain rangelands and its fauna requires designing an appropriate habitat restoration strategy that incorporates the traditional Gadda system of grassland management, whilst also mitigating possible adverse effects on rural livelihoods. MMU PhD student Bruktawit Muhamued has been working on the Liben Plain collecting ecological data on this ‘Critically endangered’ bird along with socio-economic information on local livelihoods and lifestyles. Working with Huw Lloyd and Stu at MMU, along with Nigel Collar (BirdLife International), Paul Donald (RSPB), and rangeland ecologist James Bennett (Coventry University), Bruk is creating an important evidence base to find compromises good for both people and the lark. 

The Liben Plains with Boran cattle. Photo: Paul Donald

Since June 2013, we have been collecting data on the abundance, foraging behaviour, and habitat associations of the lark. These data will enable Bruktawit to estimate the Lark’s global population size, to determine whether it is restricted to areas of traditional Gadda managed grassland habitat and how the species responds to shifting land use practices brought about by changes to the economic realities faced by native pastoralists.

Bruk prepares artificial lark nests. Photo: Huw Lloyd

Perhaps the best hope for lark’s survival has come from an unlikely source. A few years ago we found small patches of longer grass on the overgrazed plain – areas where the cows seemed not to want to feed. Even stranger was that these areas were dotted with white hyena dungs – and it was this pooh that the cows were avoiding. We wondered whether we might be able to use hyena excrement to create small patches of nesting habitat in an otherwise overgrazed landscape. The scats would act as a biological control to reduce overgrazing – just as people use wolf urine or tiger faeces to deter deer and other ‘pests’ from entering gardens and fields.

Bruk is using artificial nest experimental plots demarcated with hyena dung, which will enable her to monitor the natural restoration of grassland vegetation, and determine the survival rates of the artificial nests. Hyena dung collection has been one of the most challenging aspects of her first fieldwork season! 

Spotted Hyena and the 'white gold' that is its dung. 
Photos: Bruk

Hyenas regularly come into contact with rural and small urban populations in Ethiopia, feeding in close proximity to rural houses and rubbish dumps. The challenge is to collect not only enough pooh but also dung of the right quality! There are several locations in the region where this is possible, although sometimes, the local hyenas can become a little puzzled or inquisitive at the unusual interest in their waste products!

Bruk's PhD is supported by Manchester Metropolitan University along with A.G. Leventis Foundation, RSPB and BirdLife International.

  

Dishing the dirt on Peru’s parrots

Posted by Alan Lee and Stuart Marsden

Alan Lee finished his PhD in the group three years ago. His PhD, supervised by Stu, along with Martin Jones (MMU), and Donald Brightsmith of Texas A&M University, focused on the ecology of the rich parrot community of southeastern Peru, and in particular examined how and why the various species consume clay at colpas (claylicks). Geophagy is the intentional consumption of ‘dirt’ – something which a surprising variety of animals do. Chimpanzees and a range of new world monkeys have been recorded eating dirt (often from termitaria). Herbivorous mammals such as tapir, peccary, deer, agoutis and bats have been recorded drinking salty water and eating dirt at claylicks in South America, while several publications have examined geophagy in elephants in Africa and Asia. Markets in West Africa sell small bags of special clay for pregnant women. 

Red-and-green Macaws at the Blanquillo claylick in Manu

Geophagy and consumption of mineral-rich water is common in the tropics especially among frugivorous birds such as parrots and pigeons. This said, we still do not know how common and widespread geophagy is in birds – largely because it is difficult to observe in the vast and little-known tropical forests. Previous work by Dr Craig Symes, another South African who worked in our group, recorded fourteen pigeon species and six parrot species practising geophagy, or drinking salt water in a forest in Papua New Guinea (61% of the sites parrots and 30% of parrots). Cassowary was recorded eating blue soil rich in iron and the conclusion from this study is that different birds in the area were using different dirt for different reasons (Symes et al. 2006).

Alan and Red-tailed Boa Constrictor

Before his PhD, Alan had spent a couple of years working for an NGO ostensibly to investigate the impacts of tourism on Amazonian wildlife, and volunteered on the Tambopata Macaw Project under Donald Brightsmith. He learnt a lot about the wildlife of the region but was most fascinated by the geophagy sites along the rivers of SE Peru, where parrots would flock together in the early morning, fly around noisily, look spectacularly beautiful and then some of them would descend to the river banks to munch on soil. But not always, and not evenly, and not everywhere. It was Alan’s task to figure out if there was a pattern to this spectacle – a spectacle so impressive that several successful tourist enterprises had been built on the back of this raucous feathered firework show. 

 







Together with a handful of volunteers from all walks of life, we spent hundreds of hours at many parrot geophagy sites across the Peruvian Amazon. We braved jaguars, herds of peccary, floods, rabid bats, terrorist attacks, flesh eating diseases, and a host of other difficulties to try and understand parrots and their ways. The first job was to map out across the entire continent where the claylicks were found, and to use MaxEnt, a presence-only species (or in this case, claylick) distribution model to determine where claylicks were and perhaps why they were in some areas and not others. We realised that they were only found in the western sections of the Amazon, where sodium deficits are the greatest (Lee et al. 2010).

The next job was to put the numbers of parrots which regularly use the region’s riverbank claylicks into perspective of the numbers of parrots in the areas – do all parrots visit claylicks everyday? We made many counts of parrots at various claylicks but a more difficult job was trying to survey parrots in the tall and complex Amazonian forest. This problem led us to propose a variant of Distance Sampling based on call counts which may be a useful line transect method in tall forests (Lee & Marsden 2012). In respect to geophagy, our results suggested that only a small proportion of the parrots in the area visit claylicks on a given day – the consumption of clay seems to be more of a ‘topping up’ habit than a daily necessity.

This is important in terms of our understanding of why parrots eat dirt. While several researchers have posited that the soil was being consumed for the sodium contained therein, a PhD conducted by Jamie Gilardi during the nineties had convinced much of the world that the soil was consumed in order to neutralise the natural toxins found in the seeds and unripe fruit. This is a fascinating possibility – Jared Diamond and team in a publication on geophagy and birds from Papua New Guinea highlighted the behaviour in the light of the toxin-arms race between plants and parrots who predate rather than disperse their seeds (Diamond et al. 1999). 

Dusky-headed Parakeets and Blue-headed Macaws

That claylicks are concentrated in a small portion of South America where sodium deficits are likely to be highest, and that parrots tend to visit claylicks periodically and not continuously may suggest that the reason for parrot geophagy is mineral- rather than toxin-related. A final strand of enquiry, which we are about to publish, looked at the diets of different parrot species and their tendency to visit claylicks. Again, we were unable to link geophagy to toxin neutralization - in fact, it was flower-eating successional-forest parrot species that seemed to consume more soil than those large macaws that predate more toxin-rich seeds and unripe fruit. We will detail these findings in an upcoming post.


Alan now has a postdoctoral research position at the University of Cape Town investigating how the endemic birds of South Africa's endemic biome (the Fynbos) will fare under climate change scenarios. The work is almost as exciting as it was in the Amazon – you can read all about it at http://bluehillescape.blogspot.com/

Alan's PhD research was done in association with the Tambopata Macaw Project

 


References

Diamond, J., Bishop, K.D. & Gilardi, J.D. (1999). Geophagy in New Guinea birds. Ibis 141: 181-193.

Lee, A.T., Kumar, S., Brightsmith, D. & Marsden, S.J. (2010) Distribution of claylicks and their use by parrots across South America: Do patterns of where help answer the question why? Ecography 33: 503-513.

Lee, A.K.T. & Marden, S.J. (2012). The influence of habitat, season and detectability on abundance estimates across an Amazonian parrot assemblage. Biotropica 44: 537-544.

Symes, C. T., Hughes, J. C., Mack, A. L. & Marsden, S. J. (2006). Avian geophagy in the Crater Mountain Wildlife Management Area, Papua New Guinea. Journal of Zoology 268: 87-96.