Garden structure is for the birds!

Cities and urbanisation

Urbanisation is a known and major driver of global biodiversity loss. It is also true that urbanisation has a differential effect on species and can encourage some but deter others. Currently almost half of the world’s 7.8 billion human population lives in cities and this is expected to reach 60% by 2030. This makes it important to change the way we operate in these urban areas if we wish to ensure that our life support systems which are derived from nature and the flow of ecological processes are able to continue. Natural areas such as reserves and parks have been empirically shown to improve the standard of living of people in cities and can affect attitudes to natural ecosystems and conservation. Therefore, the quality of urban environments and particularly of urban green spaces, is increasingly an important issue for human health in our concrete conurbations. Contemporary studies have highlighted the critical roles of urban nature reserves and managed green spaces for supporting both local and even regional biodiversity.

Most of us are aware of the importance of green spaces within our city through the D’Moss programme, the work done by conservancies and because of what we see when we interact with them through bird clubs, butterfly groups, hiking and bicycle trails but do we ever really consider how valuable our gardens can be? The Covid-19 pandemic and our national lockdown have certainly meant that people take a much closer and intimate look at their own backyards. Here we look at what our gardens mean, and can mean, to local and regional biodiversity by examining their structure and our own perceptions of what makes a garden great for birds. The birds profiled are all species of the Upper Highway area that you should see in your garden if it is structured for nature.

Garden structure and bird diversity

An Olive Sunbird feeding on nectar at an Erythrina caffra flower

There have been many books, articles and blogs written about the value of planting indigenous species in your garden. As a nature-aware community many of us have evolved from just planting indigenous, through to being aware of what is regionally indigenous. Indigenous plants very obviously remain important from the point of view of providing the food birds need to survive and thrive in a way that non-native or alien plants cannot do. Some of this relates to the production of fruit, nectar and seeds but also perhaps even more significant is the dependence on insect populations, as most land birds require insects to feed growing young so there is a direct and profound effect on breeding success and survival.

Klaas’ Cuckoo male (right) courtship feeding a female (left)

A garden’s 3-D architecture

For birds in urban environments, the configuration of local habitat within the landscape may be as critical as the composition of the local habitat itself. Specific landscape characteristics such as the vegetation structure are now being recognised as one of the most important factors that impact bird species diversity in an area. Not all birds have the same habitat preferences and different species thrive under different conditions with some preferring dense vegetation while others prefer more open habitat.

For maximum species diversity habitats need to have variety and to include canopy and understory plants, degree of openness and be as unmanicured as possible. When it comes to considering the ecological value of a garden it’s what could be called their 3-D architecture.

Structure wild style – a landscape of layers with large woody species overtopping a dense herbaceous understory

Whether you live in an urban apartment or have a large residential or rural plot, your outdoor area is more than just a private space. Ecologically, a garden is another jigsaw piece in the landscape.

Vertical and horizontal structure, which comes from multiple layers of different plants at different heights, provides many more niches than an expansive lawn lined with manicured hedges and neatly trimmed topiaries. One of the main characteristics of urban areas is the numerical dominance of a few abundant bird species. So in order for gardens to be frequented, used and lived in by more than the usual garden generalist species, you need to think a little more about the bush we go to visit when we want to relax and enjoy wildlife. Think of the structure that exists around the edge of a bushcamp and that’s where parts of your garden, if not all of it, needs to be heading.

Build it and they will come

A mix of old mature trees – there is nothing that can replace these within a habitat – middle story and understory. If you have the space in your patch for an ecotone habitat – an area of smaller shrubs, herbs and annuals in between open habitats and forest, this will create this important niche. The love of lawns comes at such a high cost, with higher water demand and fertiliser/herbicide combinations adding to the environmental issues of lowered carrying capacity.

In addition, the simplistic plant choices, the same plants favoured for landscaping which are used over and over again in different gardens, compound the issues by creating uniform habitats that limit biodiversity. The most common bird species seen in our urban gardens are generalists and will be found in gardens with low to high ecological value. Dark-capped bulbuls for example are fruit eating generalists that have no specific habitat preference and are found in open to forested habitats.

Dark-capped bulbuls are one of the more common generalist birds found in the upper highway gardens

Getting the more unusual or specialist bird species to your garden requires a little more natural architecture. Lesser Honeyguides and Ashy Flycatchers will come to forests each looking for specific food items. Laying the table without having the right ambience doesn’t really work. Another example comes from the seed-eaters. Putting out seed will attract many of the seed-eaters but coaxing Red-backed Mannikins to spend time in your gardens requires forest margins and thickets.

Ashy Flycatcher and Lesser Honeyguide will visit gardens which provide their habitat requirements for forest and thickets

Red-backed Mannikins will visit forested and more densely vegetated gardens

Part of building the structure of a garden is to have what is perceived as ‘no structure at all’ and this includes not cleaning a garden continuously which is how we used to think about gardening –trimming, cleaning and tidying until there is very little that could be considered habitat left to host wildlife. Many species don’t like regular disturbances which are brought about by trimming hedges, lawns and stray branches on a continuous basis.

Collared Sunbird pairs also enjoy wilder garden structures and will nest and stick close to a territory if it provides the right components of cover, food and quieter nesting areas.

Leaf, branch and fruit fall are important sources of food for species such as robins and thrushes that forage on the ground and leaf litter and old wood provides important habitat for food organisms. Old decaying trees far from being ugly also provide important food and nesting habitats. This particular log (photo) was being investigated by a pair of Red-throated Wrynecks as a potential nesting site and in turn the pair of Wrynecks was being closely tracked by a pair of Lesser Honeyguides who were hoping for them to provide their brood parasite service – two uncommon species pulled in by the presence of a single dead tree.

Red-throated Wryneck investigating cavities in a dead tree trunk as a potential nest site

Not just the size that counts but the structure

Whatever their size, a garden can contribute to natural functions and processes in the local area, such as regulating water drainage, buffering the damaging effects of strong winds, or providing food and shelter for all sorts of birds and other wildlife if structure is allowed to mimic natural habitat structure. The network of parks, nature reserves and open spaces in the Upper Highway area is important but these areas can be significantly supplemented by the actions taken in individual gardens. Gardens are a significant proportion of the area of green space when the whole area is considered and, in this area, forms up to 50% or more of the urban landscape. Collectively they therefore provide unique and undervalued resources for enhancing urban biodiversity. Gardens if considered as significant habitats in their own right, improve connectivity by functioning as corridors or by collectively enlarging the size of adjacent habitats irrespective of individual size.

In this regard it has been interesting to collate the bird lists from the Upper Highway area from those participants in BirdLife Port Natal’s Bird Count Lockdown Challenge. This has suggested that longer bird lists don’t necessarily emanate simply from larger properties but rather follow the level of wildness and structure of the gardens and surrounding habitats.

Blue Waxbill and Red-billed Firefinch recently recorded in the Lockdown garden challenge could become much more common with a collective urban landscape agenda.

A new landscape paradigm

Perhaps we need to be thinking more broadly about our urban landscapes and managing gardens more as a collective landscape, rather than individual gardens. This would not only increase diversity but also the carrying capacities of our urban areas while also enhancing the regional movements of birds. Changing our cultural expectations and assumptions about gardens has to blend our society-imposed sense of order with the perceived sense of disorder in nature – the very same disorder that we flock to in the ‘bush’ when on holiday.

The same landscape that mentally and physically heals us but it is somehow not good enough for where we live. And so, we come back to the title of this article. Structure, if we consider the presence of a canopy, understory, ecotones and habitat mosaics made up of adjacent forests and grasslands IS for the birds while removing fallen winter leaves, dead wood and trimming hedges is not. The way in which we structure (or don’t) our gardens is important if we are to reverse the trends of species loss, and bring about natural systems that are self-sustaining and provide many more benefits that we realise, although one of them is definitely to see more birds in our home patches.