Hollow Ecosystems: Ambient Shelters for Avifauna in Cities

Hollow Ecosystems (HES) can encourage a healthy population of birds within urban areas as well as add value of wonderment to architectural projects.

Typology of enclosures i) shielded type ii) partially enclosed type iii) open type. They maybe adopted depending on environmental conditions around the site. (Illustrated for Expanded Environment by author).

Cities are home to several species of birds which add to aesthetics, mood and vitality. For instance, Warsaw in Poland houses 65 per cent of all bird species in the country [i]. But the urban environment can also be really harsh on the avifauna causing stress that affects health and reproduction [ii]. Emissions, noise and lights in the city have been particularly recorded to discourage birds in the urban areas [iii][iv]. In addition, human interference and feral predators like cats and dogs are threats to birdlife in cities [v]. Thus, the avifauna need defined spaces in urban areas for not just providing them shelter – but also shielding them from the brutal environmental conditions in cities. Architectural interventions broadly categorised under Hollow Ecosystems can contribute towards this necessity.

Hollow Ecosystems – bird shelters with ambience for wonderment

Traditional shelters for birds like dovecotes or modern interventions like that of Ned Dodington’s Swift Tower are but examples that exemplify human-made refuges for the avifauna. In comparison, the Hollow Ecosystem (HES) concept can perhaps be more closely associated with aviaries which are built not only as shelters but also for the visual appreciation of bird-life. Very early since I was a student, I began experimenting with cavities in walls that not only provided shelter for birds but also restricted human entry and even had space for planters, to create a comfortable habitat as refuge. One of my early efforts which had articulated this idea was the Lava Columns (see figure below).  The term “Hollow Ecosystem” however, was coined much afterwards when I observed a common characteristic emerging from my designs.

Lava Columns : inspired from the amorphous flow of lava which brings vitality. Source: Deb, A., Jayashankar, M., 2012.

Along with my zoologist colleague M Jayashankar, I first suggested the concept of HES with a series of designs in 2012 at International Conference for Conservation of Sparrows [vi] held at Bengaluru. It went on to be awarded the best proposal. The model hypothesises that birds can seek refuge by flying in and out of hollow shells with least interference from humans or other legged predators. Two key characteristics of HES structures are: (a) partial enclosures that created shelters for birds (b) layer of biological growth creating a micro-climate inside the enclosures. The HES structures are bound to create an ambience within. This set up creates a unique man-made physical environment for the birds, and is thus referred to as an ecosystem.

The HES concept is meant to define aerial spaces for birds, enabling architecture to play a lead role in biodiversity conservation. The shelters can be configured to shield birds from light, air and noise pollution that is prevalent in the urban scene. The shell is conceptualised with ivy and creepers that screen from pollution and noise; provide green cover to create ambient temperature and appeal; requiring low maintenance and adding minimum weight. Nesting niches incorporated in the design become an additional advantage for the avifauna during breeding seasons. The shells can either be built in situ or be casted off site to be retrofitted on existing buildings to boost biodiversity in cities.

The structure of the shell was envisioned to be constructed in a variety of ways. I am particularly fond of the model ‘Catherine Gardens’ that portrays a sturdy frame – a spherical segment – covered with mesh to allow the ivy to grow on one side – leaving the other open for viewing. While on one hand the shell shields birds from the external environment; it also allows an inward interface for visual interaction for humans; to appreciate the novel architectural arrangement that would invite vibrant bird species.

A segment of poster on Hollow Ecosystems presented at International Conference on conservation of sparrows, 2012. Model #1 depicts the circular HES structure ‘Catherine Gardens’. See: Deb, A., Jayashankar, M., 2012.  

HES as an integral part of nature conservation

Shelters are not the only requisite for birds to thrive. Habitats must also require access to basic needs such as food and water. To that end, factoring the movement pattern of birds can point towards pathways to support their survival:

Birds make short localised trips from their shelters –essentially for foraging food, water and nesting materials broadly categorised under ‘station keeping’ activities[vii]. Research has recorded that bird species like egrets can fly up to 4 kilometres from their nests for foraging when resources are not available immediately around their colony[viii]. On the other hand, the domestic house sparrow prefers to forage closer to its shelter to avoid predation risk [ix]. Although, the range of movement can depend on several factors such as physical features on land and species, research from Cornell Laboratory of Ornithology maintains that foraging in birds take place on a daily basis throughout the day [x]. This ability of birds to travel between location of residence and source of food can enable a flexible approach to design rather than attempting to supply all resources within the HES structure.

Relying on the foraging behaviour of the birds, potential around the HES site can be tapped by enhancing blue-green components in the area. Components may include wetlands, urban woodlands, street trees, swales, ground cover, canals, ponds, lakes, reservoirs and so on. Ecological corridors provide navigation cues for birds and support a healthy biodiversity at the ground level encouraging worms, insects, fruit-bearing trees and shrubs that become food for birds. Healthy water bodies can quench thirst of bird population and provide them with fish for food. Thus nature conservation in the vicinity of site becomes an integral part of the design context; simply with birds as plea.

To conclude, HES can encourage a healthy population of birds within urban areas as well as add value of wonderment to architectural projects. While it is ideal to make food and water available within the HES shelters, developing the green and blue network in the city is crucial within the movement range of species inhabiting the HES. This triad of food, water and shelter is key to a vibrant urban habitat for wildlife.


[i] Jaramillo, M. P. B., 2015. Why concrete jungles need green spaces. [Online] Available at: http://www.bdlive.co.za/life/health/2015/08/06/why-concrete-jungles-need-green-spaces [Accessed 26 August 2016].

[ii] Sanderfoot, O. V. & Holloway, T., 2017. Air pollution impacts on avian species via inhalation exposure and associated outcomes. Environmental Research Letters, 12(8), pp. 1-16.

[iii] Liker, A. & Seress, G., 2015. Habitat Urbanisation And Its Effects On Birds. Acta Zoologica Academiae Scientiarum Hungaricae, 61(4), p. 373–408.

[iv] Ortega, C. P., 2012. Effects of Noise Pollution on Birds: A Brief Review of Our Knowledge. [Online]  Available at: http://www.bioone.org/doi/abs/10.1525/om.2012.74.1.6 [Accessed 1 October 2017].

[v] Nuwer, R., 2013. Feral Cats Kill Billions of Small Critters Each Year. [Online] Available at: https://www.smithsonianmag.com/science-nature/feral-cats-kill-billions-of-small-critters-each-year-7814590/ [Accessed 1 October 2017].

[vi] Deb, A., Jayashankar, M., 2012.  Hollow Ecosystems: Building Architecture and Sparrow Conservation in Urban Areas [Online] Available at: https://www.academia.edu/24226232/Hollow_Ecosystems_Building_Architecture_and_Sparrow_Conservation_in_Urban_Areas [Accessed 3 October 2017].

[vii] Dingle, H., 1996. Migration: The biology of Life on the Move. New York: Oxford University Press.

[viii] Nemetha, E., Bossew, P. & Plutzar, C., 2005. A distance-dependent estimation of foraging ranges of neighbouring bird colonies. Ecological Modelling , Volume 182, pp. 67-73.

[ix] Tsurim, I. et al., 2010. Foraging behavior of an urban bird species: molt gaps, distance to shelter, and predation risk. Ecology, 91(1), pp. 233-41.

[x] Bonter, D. N., Zuckerberg, B. & Sedgwick, C. W., 2013. Daily foraging patterns in free-living birds: exploring the predation–starvation trade-off. Proceedings of Royal Society for Protection of Birds, pp. 1-7.

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