Canchao Yang

In brood‐parasitism systems, geographical variations have been documented during nest defense and the egg stage, but research on host–parasitic nestling interactions is limited, especially within the same species. The begging calls of 5–6‐day‐old nestlings of the common cuckoo ( Cuculus canorus ) and its primary host, the oriental reed warbler ( Acrocephalus orientalis ), were recorded in China (Baiyangdian, Yongnianwa, and Zhalong), and acoustic parameters were analyzed. We found marked geographical variation in acoustic mimicry: Yongnianwa cuckoos exhibited the highest mimicry precision, Zhalong cuckoos the lowest. A dual strategy of conservative mimicry of high‐frequency spectral components and adaptive mimicry of low‐frequency spectral components was evident. Mahalanobis distance calculations confirmed geographical differentiation: compared to non‐local hosts, Baiyangdian/Yongnianwa cuckoos had higher acoustic similarity to local hosts, whereas Zhalong cuckoos did not. Begging call mimicry in cuckoos is a geographically structured trait; environmental drivers of this variation should be identified.

Egg recognition and rejection constitute essential host defenses against brood parasitism, with rejection decisions reflecting evolutionary adaptations shaped by cost–benefit trade‐offs. Although long‐term studies have established correlations between egg rejection behavior and parasitism risk, it remains unclear whether hosts can dynamically adjust their defenses in response to stage‐specific parasitic threats across different breeding periods. We investigated temporal variation in egg recognition and rejection latency in the green‐backed tit ( Parus monticolus ), analyzing both seasonal patterns and stage‐specific responses within breeding cycles. Our findings reveal that while rejection behavior remained consistently precise throughout the breeding season without seasonal variation, we observed a striking stage‐dependent pattern: complete acceptance of parasitic eggs during laying followed by near‐total rejection during incubation. This biphasic response contrasts sharply with patterns reported in most other host species. We propose this unique recognition strategy stems from the tit's egg‐covering behavior during laying—an adaptation likely driven by nest predation pressure that temporarily suppresses anti‐parasitic defenses. These results demonstrate that green‐backed tits have evolved independent adaptive responses to distinct selective pressures: nest predation during egg‐laying and brood parasitism during incubation. This study provides new insights into the plasticity of host defenses and suggests that species with egg‐covering behaviors may develop specialized anti‐parasitic strategies. Our findings offer important implications for understanding the evolutionary dynamics of host–parasite interactions and establish a framework for investigating recognition behaviors in other cavity‐nesting hosts.

China stands as a global hotspot for cuckoo diversity and their avian hosts, presenting an unparalleled natural laboratory for investigating brood parasitism and co‐evolutionary dynamics in avian systems. Through an extensive synthesis of published literature, verified media reports, and meticulously curated visual documentation contributed by citizen scientists, we present a comprehensive update on cuckoo–host diversity and their intricate ecological relationships across China. Our study identifies 17 cuckoo species, with 15 confirmed as brood parasites exploiting an extensive network of 142 host species spanning 74 genera and 34 families within the passerine assemblage. While we observed broad overlaps in the ranges of host body mass and egg volume across different cuckoo species, phylogenetic generalized linear mixed models reveal significant patterns of adaptive matching in both body mass and egg volume parameters between cuckoos and their respective hosts. Our findings demonstrate striking specificity in host selection, with minimal overlap in actual host species utilization among sympatric cuckoos, suggesting sophisticated niche partitioning strategies to mitigate interspecific competition. Nevertheless, critical knowledge gaps persist, particularly regarding the evolutionary dynamics of egg phenotype mimicry in relation to specific host species. Finally, we introduce a real‐time tracking program designed to engage citizen scientists in ongoing documentation of parasitism events, facilitating dynamic updates to host–parasite records.

Alarm calls in bird vocalizations serve as acoustic signals announcing danger. Owing to the convergent evolution of alarm calls, some bird species can benefit from eavesdropping on certain parameters of alarm calls of other species. Vocal mimicry, displayed by many bird species, aids defense against predators and may help brood parasites during parasitism. In the coevolutionary dynamics between brood parasites, such as the common cuckoo (Cuculus canorus), and their hosts, female cuckoo vocalizations can induce hosts to leave the nest, increasing the probability of successful parasitism and reducing the risk of host attacks. Such cuckoo calls were thought to mimic those of the sparrowhawk. However, owing to their similarity to alarm calls, we propose a new hypothesis: female cuckoos cheat their hosts by mimicking the parameters of the host alarm call. In this study, we tested this new hypothesis and the sparrowhawk mimicry hypothesis simultaneously by manipulating the syllable rate in male and female common cuckoo vocalizations and playing them in front of the host Oriental reed warbler (Acrocephalus orientalis) for examination. The results indicate that similar to a normal female cuckoo call, a female call with a reduced syllable rate prompted the hosts to leave their nests more frequently and rapidly than male cuckoo calls. Additionally, the male cuckoo calls with increased syllable rate did not prompt the host to leave their nests more frequently or quickly compared with the male cuckoo calls with a normal syllable rate. Our results further confirm that female common cuckoos mimic the vocalizations of Eurasian sparrowhawks, reveal the function mechanisms underlying such mimicry, and support the theory of imperfect mimicry.

Many animals display numerous colors that can range from red, green, blue, and orange to ultraviolet, whereas others are dull or have a uniform coloration. The reason for this variation in coloration remains unknown. It has been hypothesized that different colors represent multiple signals that either reflect different components, redundant information, or simply no longer provide reliable information regarding body quality. Here, we analyzed the highly diverse coloration of male golden pheasants ( Chrysolophus pictus) using an avian visual model from the avian visual system and related the different components of coloration to several phenotypic traits of body quality. We found that different components of plumage color correlated with the length of the body, tail, spur, and beak, suggesting that the multiple colors in male golden pheasants signal different components of body quality. In particular, tail length was correlated with many aspects of coloration, especially the green and orange colors of neck plumage, which are particularly important because male golden pheasants spread their neck plumage and show it to females during their courtship display. Therefore, these findings reveal that the plumage colors of male golden pheasants encode multiple signals that reflect their body condition during courtship displays.

Due to the rapid expansion of tourism, mining, and manufacturing, the economy of Hainan Island in southern China has experienced swift growth. However, it also brings the risk of soil pollution by mercury (Hg) as a result of increased traffic and mineral processing activities. In order to investigate the characteristics of soil Hg pollution in Hainan Island and assess the health risk, a total of 239 samples were gathered from five representative regions across the island. The findings indicate considerable fluctuations in the soil Hg concentration across the five sub-study areas, which are influenced by factors such as wind direction, mining activities, and economic development. Changjiang Li Autonomous County, situated in the downwind direction (NW) and rich in mineral resources, shows the highest soil Hg concentration (10.00–1582.50 ng·g⁻¹). Following closely are Haikou and Sanya, the two most economically developed cities on the island, with soil Hg concentrations of 8.33–321.50 ng·g⁻¹ and 6.04–180.50 ng·g⁻¹, respectively. Wuzhishan Nature Reserve and Lingshui Li Autonomous County, located in the upwind area (SE), show the lowest concentrations, ranging between 10.70–104.67 ng·g⁻¹ and 9.43–84.00 ng·g⁻¹, respectively. Both the Single Pollution Index method and the Geo-accumulation Index method were employed to assess the level of Hg pollution. The results indicate that nearly half of the sampling sites are contaminated, in which the proportion of contaminated sites in Sanya and Haikou are the highest, but the level of contamination is low; the heavily contaminated sites are predominantly found in Changjiang Li Autonomous County. However, the low Health Risk Index (HI) ranging from 0.0001 to 0.0334 suggests that although the soil is contaminated with Hg, it does not pose a substantial non-carcinogenic risk to human health.