LINKED PAPER Wing patch size predicts assortative mating but not reproductive outcomes in the Daurian Redstart (Phoenicurus auroreus). Liu, M., Zhang, J., Lin, Z., Liu, R., Zhao, C. & Deng, W.(2025) IBIS.VIEW

The Daurian Redstart (Phoenicurus auroreus) is a socially monogamous passerine species. Males display vivid black and orange plumage, while females exhibit softer gray tones (Collar, 2020; Zhang et al., 2021). Both sexes, however, share a distinctive white patch on their wings, which is typically larger and more prominent in males and has previously been regarded as an ornamental trait (Figure 1).

Figure 1. The white wing patch of a (a) male and (b) female Daurian Redstart.

In China, the Daurian Redstart is a popular small bird, commonly observed across a wide range of habitats — from urban parks and green spaces to riverside paths in rural areas. During breeding season, the male and female cooperate in building the nest, often choosing locations such as old buildings, wall crevices, or other sheltered cavities that offer safety and cover. Once the nest is completed, the female is responsible for incubating the eggs. After about 14 days, the chicks hatch, and both parents take part in feeding and caring for them until they fledge.

Figure 2. Nest of a Daurian Redstart in a brick crevice, with a female incubating eggs.

Our study focused on the white wing patch of Daurian Redstarts. We aimed to examine whether males and females tend to choose mates with similar wing patch sizes — in other words, whether individuals with larger patches prefer partners with larger ones, and those with smaller patches prefer partners with smaller ones. To address this question, we captured and measured a total of 261 pairs of Daurian Redstarts over five years of fieldwork. For each male and female, we took standardized photographs of the white wing patches and quantified their wing patch size (WPS) using ImageJ. Because previous studies have shown that plumage ornamentation may be influenced by individual body size (Hegyi et al., 2008; Purves et al., 2016), and wing length is widely used as a proxy for body size in passerines (Oficialdegui & Serrano, 2024; Dias et al., 2025), we controlled for this effect by using the residuals of male and female WPS relative to wing length. We then used a Spearman’s rank correlation test to examine whether these residuals of males and females were correlated.

Our results indicate that Daurian Redstarts exhibit assortative mating based on wing patch size, with individuals tending to choose mates that have similarly sized wing patches (Figure 3). The white wing patch indeed serves as a principal trait of assortative mating.

Figure 3. Spearman’s rank correlation between male and female wing patch size (WPS) residuals relative to wing length. The grey shaded area represents the 95% confidence interval.

This finding led us to a further question: what potential benefits might arise from such assortative pairing? Could pairs with greater morphological or behavioral compatibility experience reduced intra-pair aggression and lower stress levels, ultimately improving offspring quality and increasing reproductive success?

To test this, we examined several reproductive traits — clutch size, brood size, and nestling body condition — in relation to the difference in wing patch size between mates.

Figure 4. Left: blue-type eggs of the Daurian Redstart; middle: 5-day-old nestlings; right: 12-day-old nestlings.

To quantify the difference in wing patch area between males and females, we used Storer’s index to calculate sexual size dimorphism (SSD) in the white wing patch size of paired male and female Daurian Redstarts. Interestingly, we found no clear advantage to assortative matching (Figure 5). In other words, pairs that matched more closely in appearance did not necessarily produce more or healthier offspring.

Figure 5. Relationships between SSD and (a) clutch size, (b) brood size, and (c) nestling’s body condition. The grey shaded area represents the 95% confidence interval.

Our study adds a new case to the understanding of how ornamental traits function in assortative mating. Although Daurian Redstarts mate assortatively with respect to wing patch size, this phenotypic matching does not appear to confer any clear reproductive advantages. Several factors may account for this pattern, including extra-pair mating, predation risk, nestling behavioral traits, or environmental influences (Wells et al., 2015; Harriman et al., 2017; Mutzel et al., 2019; Common et al., 2024). Overall, our findings suggest that wing patch size functions primarily as a social or signalling attribute rather than as a direct indicator of individual fitness.

In the future, we plan to collect data from Daurian Redstart populations across multiple sites and continue exploring their behavioral and physiological traits. We hope to use stable isotope analysis to trace the migratory origins of wintering individuals and examine whether migratory behavior influences blood parasite infections. In addition, we also aim to investigate how environmental factors – such as temperature and the degree of urbanisation – shape the physiological responses of Daurian Redstarts.

Acknowledgements

We thank Yongji Forestry Bureau, Jilin, China, for their permission to work on their land and cooperation. We also express our sincere gratitude to the volunteers for their assistance in the fieldwork; without their support, our field studies would not have been possible.

Figure 6. All team members involved in the fieldwork

References

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Dias, T., Lemoine, N. P., Yanco, S. W., Zimova, M., Bay, R. A. & Weeks, B. C. 2025. Long-term increases in wing length occur independently of changes in climate and climate-driven shifts in body size. Proceedings of the Royal Society B: Biological Sciences 292:20242556.VIEW

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Purves, E. F., Conboy, M. A., Robertson, R. J. & Martin, P. R. 2016. Does white tail patch size indicate quality in male Cerulean Warblers (Setophaga cerulea)? The Wilson Journal of Ornithology 128(2):343-354.VIEW

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Zhang, J., Møller, A. P., Yan, D., Li, J. & Deng, W. 2021. Egg rejection changes with seasonal variation in risk of cuckoo parasitism in Daurian redstarts, Phoenicurus auroreus. Animal Behaviour 175:193-200.VIEW

Image credit
All images were taken by © Meijun Liu.