Nest Camouflage in Nightjars & Other Birds

Introduction

Fiery-necked Nightjar

A Fiery-necked Nightjar brooding two chicks among leaf litter in Zambia.

Nesting nightjars (and other ground-nesting birds such as plovers and coursers) are a particularly neat system for studying the evolution of camouflage in the wild: they don’t build any kind of nest structure but just lay their eggs directly on the natural background, which means they depend completely on the appearance of their eggs or their own bodies for concealment. It’s also important that nests by definition are in a fixed location – so you know the bird has chosen that spot rather than happening to have landed there after being disturbed. At our study site in Zambia we have several species of nightjar, plover and courser breed out in the open in the baking heat of the late dry season. They need to make sure that their eggs (and themselves) are protected not only from predators but also dangerously high temperatures out in the sun at midday.

Jolyon and Jared

Jolyon Troscianko and Jared Wilson-Aggarwal in the field in Zambia, photographing an incubating Fiery-necked Nightjar using a UV-sensitive camera.

We’ve been studying nightjars, coursers and plovers in the field in Zambia since 2011. These birds are currently the focus of Dr Nick Horrocks‘s work on thermal ecology. They were previously the focus of a BBSRC-funded research project in collaboration with the Sensory Ecology Group Exeter University, co-led by Exeter’s Dr Martin Stevens and carried out by Dr Jolyon Troscianko and Jared Wilson-Aggarwal. Please read more about our work on the ProjectNightjar website, help us with our research by posing as a predator in an online computer game and exerting some natural selection on ever-evolving populations of virtual eggs, have a look at the photo galleries below of real nightjars and coursers in the field, and join nearly half a million others in watching this very short video that our funders, the BBSRC, made using our film footage from Zambia:

Publications

  • Stevens, M., Troscianko, J., Wilson-Aggarwal, J.K. & Spottiswoode, C.N. 2017 Improvement of individual camouflage through background choice in ground-nesting birds. Nature Ecology & Evolution 1: 1325-1333. Read on journal website [Open Access]
  • Troscianko, J. Wilson-Aggarwal, J., Griffiths, D., Spottiswoode, C.N. & Stevens, M. (2017) Relative advantages of dichromatic and trichromatic color vision in camouflage breaking. Behavioral Ecology 28: 556-564. Read on journal website [Open Access]
  • Troscianko, J., Wilson-Aggarwal, J., Spottiswoode, C.N. & Stevens, M. (2016) Nest covering in plovers: how modifying the visual environment influences egg camouflage. Ecology and Evolution doi: 10.1002/ece3.2494 Read on journal website [Open Access]
  • Wilson-Aggarwal, J., Troscianko, J., Stevens, M. & Spottiswoode, C.N. (2016) Escape distance in ground-nesting birds differs with level of individual camouflage. American Naturalist 188: 231–239. Read on journal website [Open Access]
  • Troscianko, J., Wilson-Aggarwal, J., Stevens, M. & Spottiswoode, C.N. (2016) Camouflage directly predicts the survival probability of ground-nesting birds. Scientific Reports 6: 19966. Read on journal website [Open Access]

Nightjar Photo Gallery

Coursers Photo Gallery

News

New paper published on Weber’s Law and mimicry

Our paper ‘Why and how to apply Weber’s Law to coevolution and mimicry’ has been published in the journal Evolution. This perspectives paper, written by Tanmay Dixit, Eleanor Caves, Claire Spottiswoode, and Nicholas Horrocks, argues that Weber’s Law of proportional processing can lead to otherwise counterintuitive predictions about the evolutionary trajectories of mimicry systems.  Weber’s Law states that when the magnitude of a stimulus is large, it is more difficult to discriminate a change or difference from that stimulus. In other words, relative differences are more salient than absolute differences. We show that Weber’s Law could have implications for mimicry: when stimulus magnitudes are high, it should be more difficult to discriminate a model from a mimic. This leads to testable predictions about evolutionary trajectories of models and mimics. We also present a framework for testing Weber’s Law and its implications for coevolution. 

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New paper on evolution of egg signatures

Our paper “Hosts elevate either within-clutch consistency or between-clutch distinctiveness of egg phenotypes in defence against brood parasites” has just been published in the journal Proceedings of the Royal Society of London B. In this study, led by Eleanor Caves, we asked how host eggs evolve adaptations that allow them better to discriminate their own eggs from parasitic eggs. Theoretically, hosts can generate their own individually-distinctive egg ‘signatures’ by laying eggs that appear similar to one another (consistency) but look very different from other individuals’ eggs (distinctiveness). In this new study, we show that host species of two African brood parasites deploy either consistency or distinctiveness, but not both, as defences, and achieve distinctiveness by combining egg colours and patterns in unpredictable combinations.

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Mairenn Attwood awarded Cambridge teaching prize

Congratulations to Mairenn Attwood for being awarded the Janet Moore Prize for teaching in the Department of Zoology at the University of Cambridge, for her outstanding tutorial supervision of final-year undergraduate students, who praised her breadth and depth of knowledge, enthusiasm, and friendliness.  Mairenn follows in the footsteps of Tanmay Dixit who was awarded the Janet Moore Prize in 2020. Well done both for inspiring the next generation of behavioural ecologists!

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