Explore the vast range of titles available.

The complete mitochondrial genome of Common Cuckoo (Cuculus canorus bakeri) is determined in this study and was deposited in Genbank with accession number MN067867. The length of the mitogenome is 17,457 base pairs (bp) including 13 protein-coding genes (PCGs), 22 transfer (t RNA) RNA genes, two ribosomal RNA (r RNA) genes, one control region (CR) and one short pseudo-control region. The structure is similar to mitochondrial genome of other Cuculiforme species. Phylogenetic tree shows that C. canorus bakeri is closely related to C. poliocephalus. The study has provided useful information for further studies on the evolution, genetic diversity, and phylogenetic relationships in Common Cuckoo.

Cuckoo-host interactions provide classical examples of coevolution. Cuckoos place hosts under selection to detect and reject foreign eggs, while host defences result in the evolution of host-egg mimicry in cuckoos. Despite a long history of research, egg pattern mimicry has never been objectively quantified, and so its coevolution with host defences has not been properly assessed. Here, we use digital image analysis and modelling of avian vision to quantify the level of pattern mimicry in eight host species of the common cuckoo Cuculus canorus and their respective cuckoo host-races. We measure a range of pattern attributes, including marking size, diversity in size, contrast, coverage and dispersion. This new technique reveals hitherto unnoticed sophistication in egg pattern mimicry. We show that various features of host egg pattern are mimicked by the eggs of their respective cuckoo host-races, and that cuckoos have evolved better pattern mimicry for host species that exhibit stronger egg rejection. Pattern differs relatively more between eggs of different host species than between their respective cuckoo host-races. We suggest that cuckoos may have more \"average\" markings in order to be able to use subsidiary hosts. Our study sheds new light on cuckoo-host coevolution and illustrates a new technique for quantifying animal markings with respect to the relevant animal visual system.

Avian nest design varies depending on environmental factors but may also be influenced by between‐species interactions. In the brood parasitism context, hosts may evolve nest architectures that may limit parasite access to the nest cup, reduce parasite laying success or hinder parasite chick success. Therefore, nest characteristics may reduce the likelihood or minimise the costs of being parasitised. The common redstart Phoenicurus phoenicurus is a regular host of the common cuckoo Cuculus canorus, for which cuckoo eggs are often laid outside the nest cup, resulting in low effective parasitism rates. This allowed us to evaluate variation in host nest design and test whether nest design characteristics correlate with brood parasitism likelihood and cuckoo laying success (i.e. cuckoo egg laid in the nest cup versus outside the nest cup). While recording brood parasitism events in two distant redstart populations, we documented nest cup characteristics, such as internal dimensions, materials used and nest cup position, along with the nest‐box dimensions. Cuckoo parasitism likelihood was lower for redstart nests in cavities with smaller entrances, for redstart nests with smaller nest cups and with nest cups that were built level to the rim material. For parasitised nests, cuckoo laying success was lower at redstart nests with nest cups placed further from the cavity entrance. Our results suggest a conditional process, where the cavity entrance size first prevents brood parasites access, then the cup size and the cup level in reference to the rim material affect the cuckoo choice, and finally, the nest cup position hinders cuckoo's laying success. The use of multiple nest design strategies may explain the current low effective parasitism rates in this system. Host nest design may serve as a frontline defence that could shape parasite's preferences, and consequently host nest characteristics.

Egg color polymorphism and egg mimicry are important adaptations in the game process between hosts and brood parasites at the egg stage. The ability of hosts to recognize and reject parasitic eggs based on effective egg characteristics is a crucial factor in determining the outcome of this arms race. The evolution of linear markings on eggs has been identified in several parasitic systems of common cuckoos Cuculus canorus, yet little is known about the functional adaptation of this egg characteristic. Here, we examined the recognition and utilization methods of maculation signals of eggs in the common cuckoo hosts, south rock bunting Emberiza yunnanensis, which lays eggs with linear mimetic spots, and yellow‐throated bunting Emberiza elegans, which lays eggs with dotted mimetic spots. The results demonstrated that both species of bunting hosts show moderate recognition and rejection levels towards interspecific eggs (spotted versus streaked). Moreover, during recognition, they utilized the contrast between the maculation and the egg background rather than the contrast between the maculations themselves. Our study is the first to demonstrate that two species of open‐nesting buntings use achromatic contrast (not chromatic contrast) between pattern features and egg background color to identify and reject foreign eggs. However, whether other differences in pattern features, such as pattern density, distribution, and proportion are utilized by the hosts requires further verification.

Behavioral plasticity is an adaptive or non-adaptive adjustment made by individual animals in response to environmental changes that can affect their reproductive success. In obligate brood parasitism systems, the high reproductive costs imposed on hosts can result in the evolution of strategies for protection against parasites or their offspring (eggs or nestlings). However, there has been some controversy over whether hosts can adjust the intensity of anti-parasitic behaviors according to the spatiotemporal dynamics of parasitism risk. In this study, simulated parasitism with the common cuckoo ( Cuculus canorus ) and its host Daurian redstart ( Phoenicurus auroreus ) was performed to evaluate host nest defense and egg rejection behaviors in response to seasonal changes in parasitism risk. Daurian redstarts exhibited low nest defense intensities and high egg recognition levels; however, there were no significant differences in responses to cuckoo dummies or in rejection rates for model eggs before and after cuckoo arrival. This suggests that the anti-parasitism behavior (during both frontline defense and the egg stage) of Daurian redstarts in this study system was unaffected by intra-seasonal variation in cuckoo parasitism risk. Our findings are consistent with the strategy blocking hypothesis but do not support the parasitism risk-driven adaptive plasticity hypothesis for intra-seasonal anti-parasitism behaviors. Significance Statement Whether hosts can adjust the intensity of anti-parasitic behaviors according to the spatiotemporal dynamics of parasitism risk remains unsolved. We showed that the Daurian redstart ( Phoenicurus auroreus ), a common host of the common cuckoo ( Cuculus canorus ), exhibited low nest defense intensities and high egg recognition levels, with no significant differences in egg rejection, or in responses to cuckoo dummies before and after cuckoo arrival, suggesting that the anti-parasitism behavior of Daurian redstarts in this study system was unaffected by intra-seasonal variation in cuckoo parasitism risk.

Aggression towards brood parasites is an important component of host frontline defences. Hosts sometimes adjust this behaviour based on their previous experience with the parasites. Here, we explore whether host aggression towards the parasite dummy is affected by (1) the number of parasite visits prior to the dummy experiment and (2) the time elapsed since the last parasite visit (both identified from continuous video-recordings of host nests). As a model species, we used the great reed warbler ( Acrocephalus arundinaceus ), which is a major host of the common cuckoo ( Cuculus canorus ). At our study site, this host shows high aggression towards the cuckoo and experiences high parasitism rates. We found that the hosts increased their aggression towards the parasite dummy with increasing number of previous parasite visits. Moreover, the hosts retained aggression at high levels if the last parasite visit occurred recently. However, these behavioural patterns were or tended to be significant only in host males. Our findings underscore the importance of individual experience in shaping host aggression towards brood parasites, at least in the more aggressive sex. Therefore, we recommend considering the information on prior host‒parasite interactions when planning dummy experiments, because it may contribute to a deeper understanding of the variability in host defences against brood parasitism. Significance statement This study reveals that the great reed warbler, one of the major common cuckoo hosts, adjusts its anti-cuckoo aggression based on the number of prior cuckoo visits. Male great reed warblers, in particular, become more aggressive with repeated cuckoo visits and when the visit occurred recently. These findings emphasize the role of individual experience in shaping defensive behaviours against brood parasitism and offer deeper insights into the variability of host defences. Understanding how the previous exposures to the parasite influence host aggression can refine experimental approaches and improve our knowledge of host-parasite interactions.

The reaction of birds to the nest parasite, the European cuckoo Cuculus canorus , has been the subject of extensive testing in various aspects. However, while the cuckoo is a long-distance migrant, some of its hosts are sedentary species. In this study, we aimed to investigate whether species, primarily hosts, react to the presence of the cuckoo also in the winter season. This behaviour may involve an attempt to drive the parasite away from locations that will subsequently become their breeding sites. During playback experiments conducted in the winter of 2021/2022 in Poland, we demonstrated that numerous bird species react to the male cuckoo calls in winter. These calls may be perceived as a source of danger, particularly by cuckoo hosts, who responded to this call more frequently than non-hosts and the control species (pigeon). Nonetheless, the birds’ reactions were not strong, as they did not approach the source of the call. However, our results are constrained by the limited number of cuckoo host species wintering in Poland. To better evaluate the intensity of bird responses to the male cuckoo’s call during the non-breeding season, further studies should be conducted in regions where a greater variety of species, especially those most susceptible to parasitism, overwinter.

In some populations of the host of brood parasites, more than two parasite eggs may be laid in a single nest. This phenomenon is known as multiple parasitism, representing a cost to both the host and parasite. In this study, we analysed a long-term dataset (2007–2021) focusing on multiple parasitism of the common cuckoo (Cuculus canorus) parasitizing the great reed warbler (Acrocephalus arundinaceus). The annual parasitism rate was on average 54.3% and varied between 5.8% and 92.2%, depending on the year. Out of 720 parasitized nests, double parasitism was recorded in 172 (23.9%) nests, triple in 51 (7.1%) nests, quadruple in 10 (1.3%) nests, and, exceptionally, in the years of heavy parasitism (about 90%), quintuple parasitism was recorded in three (0.4%) nests. The rate of multiple parasitism ranged from 0 to 63% inter-annually and strongly correlated with the parasitism rate and the total number of parasite eggs found. Furthermore, the number of cuckoo eggs laid per one nest increased with the decreasing daily availability of host nests that were at a suitable breeding stage for parasitism. Both genetic and egg phenotype analyses revealed that no cuckoo female laid more than one egg in the same host nest. Using data on long-term parasite–host interactions and from continuous video recording, as well as progressive methods to assign parasite offspring thus helped us better understand various aspects of multiple parasitism in hosts heavily parasitized by an evictor brood parasite.Significance statementLaying more parasite eggs in one host nest (i.e. multiple parasitism) is common in brood parasites whose nestlings share the nest with nestmates. In the species where the parasite’s nestling kills its nest mates, multiple parasitism should be rare because it is costly for the parasite. However, in host populations with high parasitism rates, multiple parasitism occurs more often than predicted. Using long-term and video-recording data, we quantified multiple parasitism in the common cuckoo across years and host egg-laying sequences. We found that the rate of multiple parasitism is positively related to the parasitism rate and that the lower the number of nests suitable for parasitism, the higher the number of parasite eggs in one nest. Based on genetic and egg phenotype analyses, we also showed that individual parasitic females avoid laying in the nests they had already parasitized.

Mimicry is a widespread phenomenon whereby predatory or parasitic individuals can access unsuspecting prey or hosts for the former’s benefit. For example, brood parasitic common cuckoos (Cuculus canorus) evolved several adaptations to trick hosts, including host-mimetic eggs, a barred chest plumage resembling the predatory Eurasian sparrowhawk (Accipiter nisus), and the female cuckoos’ bubbling calls considered as highly similar to this raptor’s calls. The sparrowhawk-like call mimicry is thought to threaten hosts while female cuckoos lay their eggs, although the similarity is restricted to the call’s fundamental frequency and not to its harmonics. However, these calls are also used in conspecific contexts, for example for mate attraction. If vocal mimicry is highly adapted toward the heterospecific function, it might cause reduced effectiveness in conspecific communication. We played cuckoo bubbling and sparrowhawk calls to territorial male cuckoos to test whether conspecific receivers process the mimetic calls accurately. All male cuckoos approached the speaker when female cuckoo calls were played, but rarely (7%) approached it when sparrowhawk or green woodpecker (Picus viridis; control) calls were played. When we excised the harmonic overtones from the sparrowhawk stimulus files, making these calls structurally more similar to the pure-tone female cuckoo calls, nearly half (43%) of the cuckoo males approached the speaker. Consequently, the difference in calls’ harmonic structure may explain one component of the inaccurate state of this acoustic mimicry. This imperfect mimicry by female cuckoos’ bubbling call to sparrowhawk call may ensure the multipurpose functions of this vocalization, including both intra- and interspecific contexts.Significance statementCommon cuckoos are obligate brood parasites, laying their eggs into other species’ nests. During laying, female cuckoos utter sparrowhawk-like vocalizations (bubbling calls), to threaten hosts and to evade their defenses. However, they also use this same call to communicate with other female and male cuckoos. If the bubbling call mimics closely sparrowhawks’ calls, cuckoos may also recognize and respond to the sparrowhawk call, the call of a predator, as a cuckoo call. We used playback experiments to show that cuckoos distinguished between bubbling and sparrowhawk calls in nearly all cases. When we manipulated sparrowhawk calls to be more similar acoustically to bubbling calls by deleting overtones, recognition errors increased from 7 to 43%. We conclude that mimicry of sparrowhawk calls by female cuckoo calls is imperfect, which allows it to function in cuckoo-cuckoo communication effectively.

Many migratory species are declining due to global environmental change. Yet, their complex annual cycles make unravelling the impacts of potential drivers such as climate and land-use change on migrations a major challenge. Identifying where, when and how threatening processes impact species' migratory journeys and population dynamics is crucial for identifying effective conservation actions. Here, we describe how a new migration modelling framework – Spatially explicit Adaptive Migration Models (SAMMs) – can simulate the optimal behavioural decisions required to migrate across open land- or seascapes varying in character over space and time, without requiring predefined behavioural rules. Models of adaptive behaviour have been used widely in theoretical ecology but have great untapped potential in real-world contexts. Applying adaptive behaviour models across open environments will allow users to explore how migratory species may adapt their routes and usage of intermediate sites in response to environmental change. We outline how SAMMs can be used to model migratory journeys through aerial, terrestrial and aquatic environments, demonstrating their potential using a case study on the common cuckoo (Cuculus canorus) and comparing modelled to observed behaviours. SAMMs offer a tool to identify the key threats faced by migratory species, how they could adapt to future migratory journeys in response to changing environmental conditions and the consequences of not being able to adapt to change.