<b>The geographic code of egg maculation: population-specific recognition cues in a cuckoo host</b>

The study area is a mosaic of land types, including villages, arboreal forests, and croplands, with tea plants (<i>Camellia sinensis</i>), eucalyptus trees (<i>Eucalyptus robusta</i>), and plum trees (<i>Prunus salicina</i>) cultivated as main crops.</p><p dir="ltr">Located in the eastern extension of the Wumeng Mountains, Liuzhi features a predominantly karst landscape with elevations ranging from 1,070 to 1,657 meters above sea level and experiences a subtropical monsoon climate.

The study area comprises a mosaic of land cover types, including villages, shrublands, croplands, and barren slopes. The primary crop cultivated in the region is maize (<i>Zea mays</i>) (Zhong et al. 2023).</p><p dir="ltr">The coevolutionary arms race between parasitic birds and their hosts has driven the evolution of host defenses, including the ability to recognize and reject foreign eggs. As a host of the common cuckoo (<i>Cuculus canorus</i>), the grey bush chat (<i>Saxicola ferreus</i>) has evolved egg recognition ability, but whether it relies on maculation patterns as visual cues remains unclear.

Field observations indicate that egg phenotypes in this species are polymorphic, solid blue and mottled eggs with a blue background and reddish-brown maculation—sometimes even within the same nest. To investigate whether the presence and type of maculation serve as recognition cues, we combined avian visual modeling with field experiments in both Yunnan and Guizhou populations, testing rejection behavior toward experimental eggs painted with either uniform red spots or lines.

Our results revealed that individuals from Yunnan population did not exhibit significantly different rejection rates regardless of the presence or type of maculation, suggesting that uniform spotting patterns are not a primary cue for egg recognition. In contrast, in the Guizhou population, experimental eggs with lined patterns were rejected at a significantly higher rate than controls, indicating that pattern type influences rejection decisions.

Additionally, the distribution of egg phenotypes differed between the two populations, with immaculate eggs being more common in Guizhou than in Yunnan populations. This study demonstrates that egg recognition cues in the grey bush chat may be population-specific and involve more complex multi-cue integration. This is the first report on intra-clutch egg color dimorphism in a cuckoo host.</p>