Evolution of pendant nests: do birds build to reduce predation risk?

Nest building is a key reproductive behaviour in birds and yet we know very little about the decision-making underpinning it, nor the evolutionary drivers of diversity in nest design. While birds of the same species often build different nests in different geographic regions, it is not clear whether this is a result of birds making decisions in response to environmental conditions, or to other factors such as predation. Similarly, whether environmental conditions, predation or other factors such as sexual selection best explain variation in bird nest design across species remains poorly understood. With this project we aim to address the extent to which birds’ nest design is shaped by predation risk at both small and large evolutionary scales.
The focus in this project would be particularly pendant nests (i.e. nests that hang from branches), arguably some of the most elaborate nests built by any bird species. These nests are intricately constructed from hundreds of strips of flexible material, requiring significant investment in time and energy and yet the fitness benefits of this costly nest design largely remain to be established. While the most famous examples are found in the weaverbirds, members of at least 11 passerine families build pendent nests suggesting that they may have evolved multiple times independently in response to common selection pressures. While it is commonly assumed that these nests are specifically designed to prevent access by nest predators, particularly snakes, this hypothesis has rarely been systematically tested. We will especially focus on the weavers as this group of birds vary widely in the shape of their nests, and especially in the presence and length of nest entrance tubes.
We will use three different ways to address this question: 1) use nests in online and museum collections such as at the Birds of the World Online, Natural History Museum collection, Tring/the Hunterian collection, Glasgow as well as in collections in Southern Africa to compare variation in morphology within and across species, and across geographical locations in Africa; 2) look at within and between species variation in extant populations of weavers (specifically white-browed sparrow weavers in the Kalahari and cape weavers in Cape Town) along with quantitative measures of predation; finally, we will use a large-scale comparative analysis to examine the factors, including predation that might explain pendant nest structure.

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Image Captions

Figure 1. Sparrow weaver roost short,Figure 2. Sparrow weaver roost long,Cape weaver colony


Fieldwork on weaver nests and roosts would be conducted in South Africa at a number of locations including the Kalahari as part of Healy’s research programme. Phylogenetic comparative analyses will be conducted with training from Sally Street.

Project Timeline

Year 1

Years 1-3 will consist of three components: i) fieldwork in South Africa collecting data on nest morphology; ii) collecting morphological data from nest collections in museums; iii) conducting a comparative analysis of avian nest structure in relation to predation and environmental conditions (with Dr Sally Street, Durham).

Year 2

Fieldwork in South Africa collecting data on nest morphology; conducting a comparative analysis of avian nest structure in relation to predation and environmental conditions. Conference attendance.

Year 3

Collecting morphological data from nest collections in museums. Possibly also field work in South Africa. Conference attendance.

Year 3.5

Finishing off data analyses; writing up thesis.

& Skills

There are multiple kinds of training that will be intrinsic to this project: field skills acquired as a result of identifying birds, ringing birds, measuring nests, both in the field and in museum collections; comparative analyses of a large data set of avian building available to Healy and Street; data analyses of the field and experimental analyses; statistical programming in R; writing papers; presenting data at lab group meetings (Healy has a weekly lab group meeting), national and international conferences; attendance at seminars (multiple available at all three sites).

References & further reading

Breen, A., Guillette, L.M. & Healy, S.D. 2016. What can nest-building birds teach us? Comparative Cognition & Behavior Reviews, 11, 83-102.
Bailey, I. E., Muth, F., Morgan, K. V., Meddle, S.L. & Healy, S.D. 2015. Birds build camouflaged nests. Auk, 132, 13-17.
Healy, S.D., Morgan, K.V. & Bailey, I.E. 2015. Nest-construction behaviour. In Nests and Eggs: Incubating New Ideas about Avian Reproduction (Ed. by C. Deeming and J. Reynolds). Pp. 16-28. Oxford University Press.
Mainwaring, M.C. & Street, S. 2021. Conformity to Bergmann’s rule in birds depends on nest design and migration. Ecology and Evolution, 11, 13118-13127.
Sugasawa, S., Edwards, S.C., Stanforth, R., Bruton, E., Hansell, M., Reilly, M. & Healy, S. D. 2021. A non-destructive approach to collect nest material data using photographs. Ibis, 163, 1457–1462.
Vanadzina, K., Street, S., Healy, S.D., Laland, K., Sheard, C. Global drivers of variation in cup nest size in passerine birds. Journal of Animal Ecology, DOI: 10.1111/1365-2656.13815.

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