Avian alarm calls mediate defenses against brood parasites and predators. These calls facilitate communication among adults and alert nestlings to potential danger. While heterospecific call recognition has been extensively studied in adult birds, nestlings—lacking direct predation experience and heterospecific alarm exposure—represent an ideal system to investigate the response to interspecific warning cues. This study explored the recognition capabilities of 5–6-day-old nestlings in Oriental Reed Warbler (Acrocephalus orientalis), a common host of the Common Cuckoo (Cuculus canorus). We exposed the nestlings to playbacks of alarm calls directed at parasites and raptors from conspecific, Vinous-throated Parrotbill (Sinosuthora webbiana, sympatric species), Isabelline Shrike (Lanius isabellinus, allopatric species) and Common Tailorbird (Orthotomus sutorius, allopatric species) adults. Results indicated that there was no significant difference in the responses of nestlings to the alarm calls of conspecific and allopatric adults directed at cuckoos and sparrowhawks. In addition, interestingly, nestlings significantly reduced their begging in response to conspecific and unfamiliar allopatric Isabelline Shrike and Common Tailorbird alarm calls but exhibited a weak response to the sympatric Vinous-throated Parrotbill. Whether older warbler nestlings with more social experience exhibit stronger responses to the alarm calls of Vinous-throated Parrotbill adults requires further investigation.

In the co-evolutionary system of avian brood parasitism, egg recognition and rejection are common and generally act as effective anti-parasitic adaptations by hosts. Accordingly, most studies have examined the role of parasite egg colors and markings in detection cues in hosts; however, studies focusing on the effects of egg size and quantity are relatively scarce and have mostly concentrated on the hosts of parasitic cowbirds. Here, we studied the egg recognition behaviors of a potential host of the Common Cuckoo (Cuculus canorus)—the Green-backed Tit (Parus monticolus), to determine: (1) whether the host uses the sizes of parasite eggs and/or the quantity contrast between parasite and host eggs as cues for recognition, (2) whether the host employs the template or discordant recognition mechanism for egg recognition, and (3) whether the size and quantity of parasite eggs affect the egg rejection modes of the hosts. The results indicate that Green-backed Tits did not use parasite egg size as a primary cue for egg recognition. We hypothesized that both visual and tactile detection might be involved in egg recognition by Green-backed Tits and suggest further studies after controlling for nest light conditions. Differences in egg quantity between parasites and hosts were not used as cues for egg recognition because the hosts employed the template mechanism rather than discordance to recognize parasite eggs. However, both the relative sizes and quantity of parasite and host eggs significantly affected the rejection modes of parasite eggs, and larger or more parasite eggs triggered higher probabilities of nest desertion in hosts.

Noise pollution is a major component of sensory pollution that can disrupt the well-being and functioning of living organisms, affect a variety of life history traits in animals, and reduce their reproductive success. In this study, we used artificial nest experiments with noise manipulation to investigate the influence of anthropogenic noise on nest predation during the breeding and non-breeding seasons and in different forest habitats. We found that the noise treatment did not alter the predation rates or survival probabilities of birds in artificial nests. However, the diversity and species composition of nest predators in artificial pine forests varied between breeding and non-breeding seasons, which may be explained by season-specific adaption of nest predators to bird nests or the unstable ecosystems of artificial forests. The diversity and species composition of nest predators differed between the different forests, probably because of differences in habitat heterogeneity. Predation time varied with treatment, season, and habitat, although most predators were nocturnal mammals. Niche segregation or changes in optimal foraging time may explain this phenomenon.

Adaptive mate choice has been accepted as the leading theory to explain the colorful plumage of birds. This theory hypothesizes that conspicuous colors act as signals to advertise the qualities of the owners. However, a dilemma arises in that conspicuous colors may not only attract mates, but also alert predators. The "private channels of communication" hypothesis proposes that some intraspecific signals may not be visible to heterospecific animals because of different visual systems. To better understand the evolution of plumage colors and sexual selection in birds, here we studied the chromatic difference and achromatic differences of melanin- and carotenoid-based plumage coloration in five minivet species (Pericrocotus spp.) under conspecific and predator visual systems. We found that either the chromatic or achromatic difference among male or female minivets' plumage was consistently higher under conspecific vision than under predator vision for all five studied species of minivets. This result indicated that individual differences in plumage colors of minivets were visible to the conspecific receivers and hidden from potential predators as a result of evolution under predation risk and conspecific communication. However, males were under a higher risk of predation because they were more conspicuous than females to the vision of a nocturnal predator.

Living and/or non-living animal models are often used as stimuli to observe the behavioral responses of the target animals. In the past, parasites, predators, and harmless controls have been used to test host anti-parasitism defense behavior, and their taxidermy specimens have been widely used as a set of standard methods for the study of avian brood parasitism. In recent years, with the rapid development of 3D-printing technology, 3D-printed bird models are expected to be applied as a standard method in the study of avian brood parasitism. To evaluate the use of 3D-printed models, this study tests the reaction of Oriental Reed Warbler (Acrocephalus orientalis) towards predators, parasites, or controls, and compares the reaction among different nest intruders and between taxidermy specimens and 3D-printed animal models. It was found that the Oriental Reed Warbler responded most aggressively to the parasite, followed by predator, and finally the control; the results were consistent between the reaction to taxidermy specimens and 3D-printed animal models, indicating that 3D-printed models could serve as a substitute for taxidermy specimens. We propose a series of advantages of using 3D-printed models and suggest them to be a standard method for widespread use in future studies of avian brood parasitism.

Here we documented up-to-date information on breeding ecology of Buffy Laughingthrush (Garrulax berthemyi), an endemic species of China, and a sympatric coordinal Red-tailed Laughingthrush (Trochalopteron milnei), in southwestern China. Furthermore, we compared breeding ecology of these two sympatric species. No significant differences were found in clutch size, egg size, nest size, nest height, nest habitat and predation rate between these two species except nests depth, nests cover and eggs color. The Red-tailed Laughingthrush nestlings differed from those of the Buffy Laughingthrush in gape morphology and the extent of down. Observation of breeding behavior showed that cooperative breeding might exist in the population of Buffy Laughingthrush.

Studies on breeding biology enable us to broaden our understanding of the evolution of life history strategies. We studied the breeding biology of the Green-backed Tit (Parus monticolus) to provide comprehensive data on nest and egg characteristics, parental behavior throughout egg laying and nestling periods, and reproductive outcome. Our study reveals adaptive behavioral patterns and reproductive strategies for P. monticolus.

The mutually antagonistic processes producing adaptations and counter-adaptations in avian brood parasites and their hosts provide a model system for the study of coevolution; this topic has long been an area of focus in ornithology and evolutionary biology. Although there is an extensive body of literature dealing with avian brood parasitism, few empirical studies have considered the effects of the coevolutionary processes associated with brood parasitism on the acoustic characteristics of parent–offspring communication. Under the strong selection pressures associated with brood parasitism, parasitic birds may, for instance, produce deceptive songs. The host may in turn evolve the ability to recognize these sounds as deceptive. At present, the mechanisms underlying the different competitive strategies employed by hosts and parasitic birds remain unclear. Here, we reviewed previous studies that investigated acoustic traits in scenarios of brood parasitism, highlighting possible adaptive functions. Using a meta-analysis, we identified no heterogeneity among studies of begging call adaptations in parasitic nestlings. However, our results may have been affected by the small number of applicable papers available for analysis. Our meta-analysis also suggested that studies of acoustic communication and transmission in adult hosts were highly heterogenous, suggesting that research methods were inconsistent among studies. Finally, we identified knowledge gaps and proposed several lines of future research.

The life history of birds dictates their activities and is crucial to population success. However, the life history traits of only one-third of the world's bird species have been described; the rest are poorly understood. We studied the breeding ecology of the Yellow-bellied Warbler (Abroscopus superciliaris) and documented reproductive information throughout the egg and nestling periods. The data included natural nest sites, nest components, nest size, egg laying dates and time, egg morph, egg size, clutch size, egg incubation, nestling brooding and feeding, nestling morph and growth, and reproductive outcome. This study provided particular information of breeding ecology that has not been reported before in the Yellow-bellied Warbler.