Differential fitness effects of moonlight on plumage colour morphs in barn owls

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The Moon cycle exposes nocturnal life to variation in environmental light. However, whether moonlight shapes the fitness of nocturnal species with distinct colour variants remains unknown. Combining data from long-term monitoring, high-resolution global positioning system tracking and experiments using prey, we show that barn owls (Tyto alba) with distinct plumage colourations are differently affected by moonlight. The reddest owls are less successful at hunting and providing food to their offspring during moonlit nights, which associates with lower body mass and lower survival of the youngest nestlings and with female mates starting to lay eggs at low moonlight levels. Although moonlight should make white owls more conspicuous to prey, it either positively affects or does not affect the hunting and fitness of the whitest owls. We experimentally show that, under full-moon conditions, white plumage triggers longer freezing times in prey, which should facilitate prey catchability. We propose that the barn owl’s white plumage, a rare trait among nocturnal predators, exploits the known aversion of rodents to bright light, explaining why, counterintuitively, moonlight has a lesser impact on the whitest owls. Our study provides evidence for the long-suspected influence of the Moon on the evolution of colouration in nocturnal species, highlighting the importance of colour in nocturnal ecosystems.

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Fig. 1: Colour variation in barn owls.

Isabelle Henry

Fig. 2: Parental food provisioning depends on moonlight and parental plumage colouration in the barn owl.
Fig. 3: Probability of response and time spent frozen of common voles as a function of barn-owl plumage colouration and moonlight conditions.
Fig. 4: Offspring body mass and survival depend on moonlight and parental plumage colouration in the barn owl.
Fig. 5: Plumage colouration in association with moonlight levels on the night females laid the first egg of a clutch.

Data availability

The data that support the findings of this study are available at https://doi.org/10.6084/m9.figshare.c.4712765.v1. The GPS data used to assess hunting success is stored in Movebank (www.movebank.org) and accessible under the project named ‘Barn owl (Tyto alba)’ (Movebank ID 231741797).

Change history

  • 05 November 2019

    The ‘Data availability’ statement has been amended to reflect where the data are deposited; the first sentence now reads “The data that support the findings of this study are available at https://doi.org/10.6084/m9.figshare.c.4712765.v1”.


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We thank P. Ducouret for setting the video system to record the voles’ behaviour, J. Buser for his guidance and help in housing the voles in the animal facilities, I. H. Dufresnes for her help with the long-term barn owl database and for providing the picture in Fig. 1, P. Guillemin for helping prepare the data on adult food provisioning, P. Christe for giving us access to the Longworth live traps, K. Safi for helping us with the analysis of the GPS data and the people that have been involved in monitoring our barn-owl population over the last 20 years. We thank L. Keller, B. Milá and J. Delhaye for providing comments on early versions of the manuscript. We acknowledge funding from the Swiss National Science Foundation, ref. 173178, to A.R.

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A.R., A.A. and L.M.S.-J. conceived and designed the study. A.R., P.B., B.A., R.S., K.S. and C.G. collected the field data on barn owls. R.S., K.S. and C.G. conducted the GPS-tracking study with contributions from P.B. and B.A. L.M.S.-J., C.J., A.Q. and A.O.-X. designed and conducted the behavioural experiments with voles. L.M.S.-J. conducted the statistical analysis with the contribution of R.S. L.M.S.-J. and A.R. wrote the paper, with major contributions from A.R., A.K., and R.S. and with input from all co-authors.

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Correspondence to Luis M. San-Jose or Alexandre Roulin.

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San-Jose, L.M., Séchaud, R., Schalcher, K. et al. Differential fitness effects of moonlight on plumage colour morphs in barn owls. Nat Ecol Evol 3, 1331–1340 (2019). https://doi.org/10.1038/s41559-019-0967-2

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