Weak influence of natural vegetation in urban green spaces compared to agricultural ecosystems on House Martin populations: Insights from nationwide citizen science data in the Czech Republic

1.   Introduction

Antagonistic coevolution between parasitic birds, such as the Common Cuckoo (Cuculus canorus) and their hosts, has been recognized as a model system for studying the coevolutionary arms race (Davies, 2000). As successful brood parasitism severely reduces or eliminates host reproductive output (Øien et al., 1998; Krüger, 2007; Davies, 2015), hosts have evolved a range of antiparasitic strategies to cope with brood parasitism by cuckoos (Feeney et al., 2014; Soler, 2014). In turn, parasites optimize their deceptive strategies to increase their chances of successfully parasitizing the host (Davies, 2011). Despite significant progress in the study of coevolution between cuckoos and their hosts in recent decades, it is still not well known why some potential hosts are not parasitized. Understanding which hosts the cuckoos choose to parasitize and which they do not, may lay the foundation for further addressing this question.

The study of brood parasitism in birds began in Europe (Chance, 1940). The Common Cuckoo is the only brood parasite in most parts of Europe; however, it utilizes up to 276 host species (Mann, 2017). China is among the countries with the richest diversity of parasitic cuckoo species in Asia and even the world, with 17 species, many of which have overlapping distributions (Zheng, 2023; see also Fig. 1). However, for many cuckoo species, little information is available on their reproductive ecology and host utilization. Yang et al. (2012) identified 55 host species utilized by 11 cuckoo species in China. However, 13 years have passed since this previous study. Therefore, it is essential to update the information on host utilization by cuckoos in China using recent data.

Figure  1.  The distribution of 17 cuckoo species in China.

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2.   Methods

We collected information through three methods. First, we monitored brood parasitism in passerine bird nests within Jindong County, Pu'er City, Yunnan Province and Qubei County, Wenshan City, Yunnan Province from 2022 to 2024. We focused on parasitized nests, identifying the host species through photographs or videos. The parasitic cuckoo species were identified using multiple methods, including the characteristics of parasitic eggs, external morphology of nestlings, and DNA analysis of nestling blood samples. Second, we searched for published information on cuckoo hosts from local Chinese journals or relevant papers or books published by Chinese ornithologists. Third, we searched short video platforms, such as Douyin and Kuaishou, for information on cuckoo parasitism, reaching out to the video creators whenever possible to inquire about the time, location, and species involved in their footage. For the parasitic events found in the videos, we identified the species based on the morphological characteristics of the host and the parasitic chicks (Supporting media). Videos where the characteristics of the parasitic chicks were not distinct and could not be identified through morphological features, or where the videographer could not be reached and the shooting location could not be determined, were not included in the statistics.

3.   Results

We collected a total of 1155 valid cuckoo parasitism records involving 87 host species and 12 species of cuckoos (Appendix Table S1). However, we did not obtain any records of brood parasitism for five cuckoo species. Among the 12 recorded cuckoo species, except for the Chestnut-winged Cuckoo (Clamator coromandus) and Asian Koel (Eudynamys scolopaceus), which were non-exclusive parasitic cuckoos (i.e., the parasitic cuckoo nestlings can coexist with the host's nestlings in the nest and are fed by the host parents), the remaining 10 species were exclusively parasitic. In these species, upon hatching, the cuckoo nestlings will push the host eggs or nestlings out of the nest to monopolize the host's care. All 87 host species were passerine birds, belonging to 26 families, namely Aegithinidae, Laniidae, Turdidae, Oriolidae, Motacillidae, Troglodytidae, Dicruridae, Sturnidae, Timaliidae, Pnoepygidae, Phylloscopidae, Alcippeidae, Rhipiduridae, Cisticolidae, Scotocercidae, Acrocephalidae, Muscicapidae, Emberizidae, Zosteropidae, Corvidae, Paradoxornithidae, Artamidae, Hirundinidae, Fringillidae, Sylviidae, and Leiothrichidae. The families with the most parasitized species were Muscicapidae, Phylloscopidae, and Leiothrichidae, accounting for 21.8%, 9.2%, and 9.2% of all hosts, respectively. Among the cuckoo species, the Common Cuckoo utilized the most host species, covering 38 species across 13 families, accounting for 43.7% of all hosts (Appendix Table S2). The Large Hawk-cuckoo (Hierococcyx sparverioides) utilized 10 species, primarily belonging to the family Leiothrichidae, which accounted for 60% of its hosts. The Indian Cuckoo (Cuculus micropterus) utilized 13 species from 12 different families. The most parasitism cases were recorded for the Common Cuckoo, totaling 826, which represented 71.5% of all parasitism cases (n = 1155).

Although all 12 cuckoo species utilized multiple hosts, there were different cuckoos utilizing few records of the same host, with only 26.4% (23/87) of hosts being utilized by more than one cuckoo species (Appendix Fig. S1).

Our nationwide survey of brood parasitism documented interactions across 32 provincial-level administrative regions. Analysis revealed pronounced biogeographical patterns: In southern China, Guizhou and Yunnan Provinces emerged as primary host biodiversity hotspots, sustaining 29 (34.5%) and 16 (18.4%) host species respectively. In northern China, the provinces with the most host species discovered are Shandong and Gansu, with 11 and 8 species respectively, accounting for 12.6% and 9.2% of the total species. Overall, the number of host species discovered in southern China is greater than that in the northern regions.

4.   Discussion

Our recent data indicate that 12 species of cuckoos in China parasitize 87 host species belonging to 26 families of passerine birds. The families Muscicapidae, Phylloscopidae, Leiothrichidae, Emberizidae, and Acrocephalidae are among the most frequently utilized, collectively accounting for more than half of the total hosts. There was significant variation in the host species utilized by different cuckoo species. For example, some cuckoos were generalists, parasitizing hosts from multiple families, such as the Common Cuckoo and Indian Cuckoo. In contrast, some cuckoos were more specialized, parasitizing hosts primarily from specific families. For instance, the Chestnut-winged Cuckoo and Large Hawk-cuckoo predominantly parasitized species within the family Leiothrichidae.

The Chestnut-winged Cuckoo mainly breeds in eastern, central, southwestern, and southern China as well as in Hainan Province (Liu and Chen, 2021). In China, the Chestnut-winged Cuckoo has been recorded to parasitize four Leiothrichidae species, including the Greater Necklaced Laughingthrush (Pterorhinus pectoralis), Chinese Hwamei (Garrulax canorus), Masked Laughingthrush (P. perspicillatus), and Chinese Babax (P. lanceolatus), and one Muscicapidae species, the Oriental Magpie-robin (Copsychus saularis) (Yang et al., 2012; Huo et al., 2014). This is similar to the findings of Praveen and Lowther (2020) in India and Sri Lanka, showing that the Chestnut-winged Cuckoo primarily parasitizes the Greater Necklaced Laughingthrush, Lesser Necklaced Laughingthrush (G. monileger), Striated Laughingthrush (G. striata), Rufous-vented Laughingthrush (P. gularis), Blue-winged Laughingthrush (Trochalopteron squamatum), and Grey-sided Laughingthrush (P. caerulatus), which all belong to the family Leiothrichidae. In addition, Huo et al. (2014) quantified the spectral characteristics of eggs, revealing that the egg color of the Chestnut-winged Cuckoo was much more similar to the egg color of the Chinese Hwamei than the Chinese Babax.

Compared with the results of Yang et al. (2012), the Large Hawk-cuckoo has been newly observed to parasitize the nests of three additional host species: the White-bellied Redstart (Luscinia phaenicuroides) (Huo et al., 2016), Ashy-throated Parrotbill (Ianthocincla cineraceus), and Rufous-necked Laughingthrush (Pomatorhinus ruficollis). These new parasitism records were all discovered in the southwestern region of China. The eggs laid by the Large Hawk-cuckoo in the nests of the White-bellied Redstart and Rufous-necked Laughingthrush were plain white and unspotted. The White-bellied Redstart is a common host for the Common Cuckoo and is known for its strong ability to recognize and reject foreign eggs (Hu et al., 2013). However, the pure white eggs of the Large Hawk-cuckoo differ significantly from the pure blue eggs of the White-bellied Redstart. Huo et al. (2016) only recorded one instance of parasitism by the Large Hawk-cuckoo on the White-bellied Redstart over several years of field monitoring in Guizhou. It led them to speculate that this may have been an accidental parasitism event.

The Indian Cuckoo is distributed in all provinces of China except Xinjiang (Zheng et al., 2023). This species has been reported to parasitize the nests of six host species (Yang et al., 2012), with the Azure-winged Magpie (Cyanopica cyanus) and Black Drongo (Dicrurus macrocercus) identified as its primary hosts. Recently, we have also discovered three additional host species parasitized by the Indian Cuckoo: the Brown Shrike (Lanius cristatus), Black-naped Oriole (Oriolus chinensis), and Ashy Woodswallow (Artamus fuscus). In Siberia, the Brown Shrike has been recorded as a host of the Indian Cuckoo (Lowther, 2017). Cases of Indian Cuckoo parasitism on the Brown Shrike have been observed in both Jilin and Liaoning provinces in China, suggesting that the Brown Shrike is a common host for the Indian Cuckoo. The Brown Shrike is a frequent host for the Common Cuckoo in China. Since both the Common Cuckoo and the Indian Cuckoo coexist in Jilin and Liaoning provinces, it is not clear whether the Brown Shrike is parasitized by both cuckoo species simultaneously.

The Common Cuckoo is currently the parasitic bird with the most host species recorded in China, parasitizing 38 host species. These hosts include 10 species from the family Muscicapidae, 6 from the family Emberizidae, 5 from the family Acrocephalidae, 4 from the family Laniidae, 3 from the family Paradoxornithidae, 2 each from the families Motacillidaehe and Corvidae, and one species each from the families Phylloscopidae, Cisticolidae, Fringillidae, Hirundinidae, Sylviidae, and Zosteropidae. Compared with the estimates in Europe, where the Common Cuckoo is known to parasitize at least 135 host species (Erritzøe et al., 2012), the number of host species for the Common Cuckoo in China is relatively small. When compared with estimates in Japan, where 20 host species for the Common Cuckoo have been documented (Nakamura et al., 1998), the number in China is not particularly large, despite significantly larger land area.

The Oriental Cuckoo (Cuculus optatus), Lesser Cuckoo (Cuculus poliocephalus), and Himalayan Cuckoo (Cuculus saturatus) primarily parasitize birds in the families Phylloscopidae and Muscicapidae. Compared with the results obtained by Yang et al. (2012), the number of new hosts for these three cuckoo species has not increased significantly. One new host of the Oriental Cuckoo has been reported, the Yellow-rumped Flycatcher (Ficedula zanthopygia) (Deng, 2013). The Lesser Cuckoo was discovered to have two new hosts, the Pygmy Wren-Babbler (Pnoepyga pusilla) (Shao et al., 2016; Wang et al., 2016) and Manchurian Bush Warbler (Horornis canturians). The Himalayan Cuckoo was found to have three new hosts, the Buff-throated Warbler (Phylloscopus subaffinis), Japanese White-eye (Zosterops simplex) (Su et al., 2014), and Yellow-streaked Warbler (Phylloscopus valentini) (Lin et al., 2024). In Yang et al. (2012), Hume's Leaf Warbler (Phylloscopus humei) was considered to be the host of Oriental Cuckoo. However, the discovery site was located in Lianhuashan, Gansu Province, where only Himalayan Cuckoo was found (Xia et al., 2016), but there were no sightings of Oriental Cuckoo. Therefore, Hume's Leaf Warbler should be classified as the host of Himalayan Cuckoo.

In China, the Plaintive Cuckoo (Cacomantis merulinus) parasitizes the nests of the Common Tailorbird (Orthotomus sutorius) (Yang et al., 2012, 2016; Tunheim et al., 2019), Dark-necked Tailorbird (Orthotomus atrogularis) (Huang et al., 2015), Rufescent Prinia (Prinia rufescens) (Yang et al., 2021), and Striated Prinia (Prinia striata) (Guo et al., 2024). Except for the Rufescent Prinia, the other three host species have also been reported as hosts of the Plaintive Cuckoo in different parts of Asia. For example, the Plaintive Cuckoo parasitizes the Common Tailorbird in Bangladesh (Nahid et al., 2016b), and the Dark-necked Tailorbird and Striated Prinia in India and the Malay Peninsula (Wells, 1999; Erritzøe et al., 2012; Praveen and Lowther, 2020). Currently, at least 18 species are known to be hosts of the Plaintive Cuckoo (Erritzøe et al., 2012; Lowther, 2017; Bllerman et al., 2020; Praveen and Lowther, 2020), and additional hosts for this species in China likely remain to be discovered.

In China, the Violet Cuckoo (Chrysococcyx xanthorhynchus) has been observed parasitizing five species of Phylloscopidae, one species of Muscicapidae, and one species of Rhipiduridae. For example, in Yunnan Province, we observed the Violet Cuckoo parasitizing the White-throated Fantail (Rhipidura albicollis), Buff-throated Warbler (Phylloscopus subaffinis), and Grey-crowned Warbler (Phylloscopus tephrocephalus). In Guizhou Province, the Violet Cuckoo was found parasitizing the Yellow-streaked Warbler (Phylloscopus valentini), Blyth's Leaf Warbler (Phylloscopus reguloides) (Yang et al., 2012), White-crowned Forktail (Enicurus leschenaulti), and Chestnut-crowned Warbler (Phylloscopus castaniceps) (Lin et al., 2024). Unlike findings in South Asia (Becking, 1981; Erritzøe et al., 2012), we did not find evidence of the Violet Cuckoo parasitizing sunbirds or spiderhunters (Nectariniidae).

In China, the Drongo Cuckoo (Surniculus lugubris) has been recorded parasitizing the David's Fulvetta (Alcippe davidi), Red-whiskered Bulbul (Pycnonotus jocosus) and Rufous-capped Babbler (Cyanoderma ruficeps), the latter of which is also utilized as a host by the Oriental Cuckoo. The Rufous-bellied Cuckoo (Cacomantis sepulcralis) parasitizes three species of Cyornis flycatchers: the Hainan Blue Flycatcher (Cyornis hainanus) (Su et al., 2016), Hill Blue Flycatcher (Cyornis whitei) (Luo et al., 2018), and Rufous-bellied Niltava (Niltava sundara) (Luo et al., 2019). The Asian Koel (Eudynamys scolopaceus) parasitizes four species of Corvidae, one species of Sturnidae, and one species of Leiothrichidae in China. Among all cuckoos, the Asian Koel has the highest rate of shared host species with other cuckoos. For instance, among six host species, the Azure-winged Magpie (Cyanopica cyanus) was also parasitized by the Indian Cuckoo and the Common Cuckoo. The Oriental Magpie (Pica serica) and the Masked Laughingthrush (Garrulax perspicillatus) were also parasitized by the Large Hawk-cuckoo. The Red-billed Blue Magpie (Urocissa erythrorhyncha) was also parasitized by the Common Cuckoo. In contrast, in Southeast Asia, the House Crow (Corvus splendens), Large-billed Crow (Corvus macrorhynchos), and Common Myna (Acridotheres tristis) are frequent hosts of the Asian Koel (Lamba, 1987; Begum et al., 2011a, 2011b; Praveen and Lowther, 2020).

In South Asia, Jacobin Cuckoo (Clamator jacobinus) and Common Hawk-cuckoo (Hierococcyx varius) primarily parasitize species in the family Leiothrichidae (Sashikumar et al., 2011; Nahid et al., 2016a; Praveen and Lowther, 2020). The Violet Cuckoo (Chrysococcyx xanthorhynchus) mainly parasitizes sunbirds and spiderhunters, and the Banded Bay Cuckoo (Cacomantis sonneratii) mainly parasitizes species in the family Ceblepyridae. In China, however, Jacobin Cuckoo, Violet Cuckoo, Banded Bay Cuckoo, Common Hawk-cuckoo, or Northern Hawk-cuckoo (Hierococcyx hyperythrus) had no hosts. There are several possible reasons for this. First, these cuckoo populations may be relatively small. Second, their distribution range within China could be quite limited, confined to certain regions. Furthermore, the Northern Hawk-cuckoo, Large Hawk-cuckoo, Common Hawk-cuckoo, and Whistling Hawk-cuckoo share similar morphological characteristics, making it difficult for non-specialist birdwatchers to accurately identify these species in the wild, which might cause misidentification, even if parasitism is observed.

In China, there are 17 species of parasitic cuckoos, and the parasitic events we have recorded involve 87 host bird species for 12 species of parasitic cuckoos (this study), while in South Asia, there are 18 species of parasitic cuckoos, and the parasitic events they have recorded involve 46 host bird species for 15 species of cuckoos (Praveen and Lowther, 2020). Although the number of host species recorded in China is greater than that in South Asia, the proportion of the same host being exploited by multiple cuckoo species in China is not significantly higher than that in South Asia (China: 23/87 vs. South Asia: 8/46). This might be related to different cuckoo species avoiding the utilization of the same host to prevent interspecific competition.

It has to be admitted that the current study had certain limitations. First, while 87 host species have been documented, the host species diversity is likely substantially underestimated due to sampling biases and underdetection of rare species, and methodological constraints in field surveys. Second, although short-video platforms provide emerging observational records of brood parasitism, their scientific utility requires critical evaluation. Key concerns include undetermined geographical provenance (many videos being reuploads from international platforms rather than original Chinese recordings) and compromised authenticity (some content creators staging parasitic interactions for viewer engagement). Nevertheless, two promising avenues may address these limitations: 1) The expanding network of citizen science among China's growing birdwatching community enhances capacity for distributed ecological monitoring; 2) Ongoing advancements in avian field research methodologies enable more systematic host species verification. Moreover, as global warming progresses, the distributions of many cuckoo species in China are gradually expanding. This suggests that the cuckoos may start utilizing new host species more frequently, eventually making them regular hosts.

CRediT authorship contribution statement

Jianping Liu: Writing – original draft, Validation, Investigation, Funding acquisition, Formal analysis, Data curation. Sidan Lin: Investigation, Data curation. Wei Liang: Writing – review & editing, Supervision, Funding acquisition, Conceptualization.

Ethics statement

No ethical approval is required for this study as it only involves references collection and analyses.

Data availability

Data used for this study are provided as supplementary material (Appendix Table S3, Figs. S2–S10, and Supporting media that can be requested from the authors for reasonable reasons).

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

We are grateful to two anonymous reviewers for their constructive comments which help improve this manuscript.

Appendix A. Supplementary data

Supplementary data to this article can be found online at https://doi.org/10.1016/j.avrs.2025.100249.