Visual modeling reveals cryptic aspect in egg mimicry of Himalayan Cuckoo(Cuculus saturatus) on its host Blyth's Leaf Warbler(Phylloscopus reguloides)

Brood parasitism and egg mimicry of Himalayan Cuckoo（Cuculus saturatus） on its host Blyth＇s Leaf Warbler（Phylloscopus reguloides） were studied in south-western China from April to July 2009.The cuckoo laid a white egg with fine brown markings on the blunt end.The eggs were conspicuously bigger than the host＇s own,with 2.06 g in mass and 1.91 cm3 in volume.Visual modeling showed that the cuckoo eggs,which from the human eye appeared to mimic the host eggs to a great extent,were completely different from the host eggs in both hue and chroma.The characters of the Himalayan Cuckoo nestling,reported for the first time,included two triangular and black patches on its gape,which appeared from four days old and became darker with age and growth.While this character also exists in nestlings of Oriental Cuckoo（C.optatus）,it has not been found for other Cuculus species.Our results reveal cryptic aspects in the cuckoo-host egg color matching,which are not visible to the naked human eye,and indicate that high mimetic cuckoo eggs rejected by hosts,as determined by human observers in previous studies,might not be mimetic as birds see them.

The effect of Common Cuckoo parasitism on the annual productivity of a host population

Avian interspecific brood parasitism is an excellent system for studying coevolutionary processes in nature because brood parasites directly affect host reproductive success.Most research on avian brood parasitism has,therefore,focused primarily on specific host anti-parasite behaviours and parasite counter-adaptations.However,the population-level consequences of brood parasitism for host species are poorly understood.This study investigated the effect of Common Cuckoo(Cuculus canorus)parasitism on the productivity of a local population of the Great Reed Warbler(Acrocephalus arundinaceus)host in south-western Slovakia.A total of 495 females nesting at the studied site successfully fledged 1321 of their own young and 63 young of the Common Cuckoo over the course of 15 years(2008-2022),and the annual rate of successful parasitism ranged from 18% to 44% over this period.As predicted,higher rates of successful cuckoo parasitism significantly reduced the annual productivity of the local Great Reed Warbler population,and its contribution to decreased host reproductive success was at about the same rate as overall nest failure caused by predation and other environmental factors.Such a heavily parasitized population was probably maintained by immigrants from other populations and density-dependent selection,which is also consistent with source-sink dynamics.However,further long-term studies monitoring parasitized populations are required to confirm these findings.

气候变化对两种候鸟物候期的影响初探——以大丰市调查为例

选取大丰市气候(1960-2007年)及两种候鸟——家燕(Hirundo rustica)(1989-2007年)和四声杜鹃(Cuculus micropterus)(1995-2007年)的物候期资料,利用一元线性回归、多元逐步回归和M-K突变检验方法,分析了大丰市气候及两种候鸟物候期的趋势变化特征及候鸟物候期对气候变化的响应关系。结果表明:(1)近48a来大丰市年平均气温上升趋势明显,倾向率为0.18℃.10a-1(P<0.01),于2004-2005年发生突变性增温;年平均风速呈极显著的下降趋势(P<0.01),总日照时数、累积降水量的变化趋势不明显(P>0.05);(2)物候期变化趋势表现在家燕始见期、四声杜鹃始鸣期均略有提早,家燕始、绝见期间隔时间略有延长,四声杜鹃间隔期以20.2d.10a-1的速率极显著缩短;(3)影响家燕始见期、间隔期的敏感气候因子是3月平均风速,影响其绝见期的敏感气候因子是5月平均温度;影响四声杜鹃始鸣期的敏感气候因子是5月总日照时数,影响其绝鸣期的关键气候因子是年平均风速、6月平均温度及7月累积降水量,影响间隔期的关键气候因子是年平均风速、6月平均温度及7月总日照时数。说明候鸟物候期对气候变化响应比较敏感,可作为气候变化的指示器。

四声杜鹃、大杜鹃寄生性繁殖习性调查

在山东日照,对两种杜鹃的繁殖习性进行了调查,调查发现:四声杜鹃(Cuculus micropterus)将卵寄生于灰喜鹊(Cyanopica cyanus)巢中,寄生率9.8%;大杜鹃(Cuculus canorus bakeri)将卵寄生于东方大苇莺(Acrocephalus orientalis)和三道眉草鹀(Emberiza cioides)巢中。

Cuckoo parasitism on two closely-related Acrocephalus warblers in distant areas:a case of parallel coevolution?

Common Cuckoos(Cuculus canorus) parasitize nests of small passerines.e Cuckoo chicks cause the death of their nest-mates when evicting eggs or nestlings from the nests;consequently,hosts su er from a high loss of reproduction.Host adaptations against parasitism,e.g.,by egg discrimination behavior,and cuckoo counter-adaptations to hosts,e.g.,by mimetic eggs,are often regarded as a result of the arms race between the two interacting species.In Hungary Great Reed Warblers(Acrocephalus arundinaceus) are the main hosts of cuckoos,su ering from heavy parasitism(ca.40-65%).e Oriental Reed Warbler(A.orientalis),formerly a subspecies of the Great Reed Warbler(A.a.orientalis),is also a highly parasitized host in Japan(25-40%).We compared main characteristics of Cuckoo parasitism in these two distant areas from the Western and Eastern Palearctic by comparing cuckoo egg mimicry.We measured color characteristics of host and parasitic eggs by spectrophotometer.Visual modeling revealed lower chromatic distances between Cuckoo and host eggs in Hungary than in Japan,but high variation both in host and Cuckoo eggs may cause matching problems in Hungary.Achromatic(brightness) di erence between host and Cuckoo eggs were lower in Japan than in Hungary,and it proved to be the most important factor a ecting egg rejection.Hosts rejected Cuckoo eggs at similar frequencies(37% and 35% in Hungary and Japan,respectively).Host adaptation,i.e.,egg rejection behavior,seems to be preceding Cuckoo counter-adaptations to hosts in Japan.We suggest that the Cuckoo-Great/Oriental Reed Warbler relationships developed in alternative ways in Japan and Hungary,and they represent di erent stages of their arms race.

A novel method to collect sperm from brood parasitic cuckoos:Urodeum stimulation(UroS)method

Sperm competition has been studied in numerous species as a representative example of postcopulatory sexual selection,where sampling sperm from male is the most basic and important step.Sperm collection can be tricky in birds,however,because unlike mammals,the genitals of birds are generally latent in the cloacal region and their characteristics vary among species.Various methods to collect sperm from different birds have been tested,such as cloacal massage,feces collection,and electro-stimulation,but their applicability varies depending on species.In this study,we introduced the urodeum stimulation method(UroS method)to collect sperm from Cuculus cuckoos,such as the Common Cuckoo(C.canorus).These species are expected to have interesting patterns of pair bonding and sperm competition because of their unique breeding strategy called brood parasitism;however,it remains unexplored.In this study,we described the application of our new method to expel semen from male common cuckoos,measured the volume of semen collected,checked the presence of sperm in the semen sample,and finally estimated its success rate among 82 males.Samples were successfully collected from 76 cuckoos(approximately 93%)and the colors and volumes of the samples were very diverse.Sperm was present in 43 of these samples(57%),showing a sperm observation rate approximately twice as high as that of the conventional cloacal massage method.We believe that this novel method will contribute to a better understanding of postcopulatory sexual selection in avian brood parasites and facilitate the process of sperm collection and artificial insemination in other medium-sized birds.

Previously unknown behavior in parasitic cuckoo females:male-like vocalization during migratory activity

Background:In the last decade,enigmatic male-like cuckoo calls have been reported several times in East Asia.These calls exhibited a combination of vocal traits of both Oriental Cuckoo(Cuculus optatus)and Common Cuckoo(Cuculus canorus)advertising calls,and some authors therefore suggested that the enigmatic calls were produced by either Common×Oriental Cuckoo male hybrids or Common Cuckoo males having a gene mutation.However,the exact identity of calling birds are still unknown.Methods:We recorded previously unknown male-like calls from three captive Oriental Cuckoo females,and compared these calls with enigmatic vocalizations recorded in the wild as well as with advertising vocalizations of Common and Oriental Cuckoo males.To achieve this,we measured calls automatically.Besides,we video-recorded captive female emitting male-like calls,and compared these recordings with the YouTube recordings of calling males of both Common and Oriental Cuckoos to get insight into the mechanism of call production.Results:The analysis showed that female male-like calls recorded in captivity were similar to enigmatic calls recorded in the wild.Therefore,Oriental Cuckoo females might produce the latter calls.Two features of these female calls appeared to be unusual among birds.First,females produced male-like calls at the time of spring and autumn migratory activity and on migration in the wild.Because of this,functional significance of this call remained puzzling.Secondly,the male-like female call unexpectedly combined features of both closed-mouth(closed beak and simultaneous inflation of the‘throat sac')and open-mouth(prominent harmonic spectrum and the maximum neck extension observed at the beginning of a sound)vocal behaviors.Conclusions:The Cuculus vocalizations outside the reproductive season remain poorly understood.Here,we found for the first time that Oriental Cuckoo females can produce male-like calls in that time.Because of its rarity,this call might be an atavism.Indeed,female male-like vocalizations are still known in non-parasitic tropical and apparently more basal cuckoos only.Therefore,our findings may shed light on the evolution of vocal communication in avian brood parasites.

Egg discrimination by hosts and obligate brood parasites:a historical perspective and new synthesis

With the knowledge that cuckoos and cowbirds lay their eggs parasitically,and that some hosts eject parasitic eggs,ornithologists began to ponder the question of how host females discriminate between a foreign egg and their own eggs,wondering how hosts 'know' which egg to remove.Results of one of the rst uncontrolled experiments were inappropriately interpreted to imply ejection was based on discordancy,with hosts simply ejecting the egg in the minority,or the 'odd-looking' egg.Controlled experiments eventually revealed that hosts rst learn the appearance of own their eggs and discriminate between them and any odd egg in their nest,regardless of which egg type is in the minority.Recent work has shown that discordancy may play a role in discrimination by males mated successively with females that lay polymorphic eggs.We examine the details of the early experiments,in light of recent advances in studies of egg recognition.An ability to recognize eggs also has been extended,implicitly,to include obligate brood parasites,as it underlies several hypotheses in explanation of the behavior of parasites toward their hosts.Egg recognition in parasites,however,has not been experimentally con rmed,nor has a mechanism been identi ed by which parasites could discriminate between their own eggs and the other eggs in a nest.We review hypotheses(parasite competition,egg removal and multiple parasitism,ma a,farming) that require the ability of obligate brood parasites to discriminate eggs at di erent levels and the potential mechanisms used by parasites to recognize their own eggs and suggest experiments to test for egg discrimination.An assessment of the egg recognition ability of parasites is germane to our understanding of how parasites counteract defenses of hosts.

Personality of hosts and their brood parasites

Brood parasites such as the common cuckoo Cuculus canorus exploit the parental abilities of their hosts,hosts avoid brood parasitism and predation by showing specific behavior such as loss of feathers,emission of fear screams and contact calls,displaying wriggle behavior to avoid hosts or potential prey,pecking at hosts and prey,and expressing tonic immobility(showing behavior like feigning death or rapid escape from predators and brood parasites).These aspects of escape behavior are consistent for individuals but also among sites,seasons,and years.Escape behavior expressed in response to a broad range of cuckoo hosts and prey are consistently used against capture by humans,but also hosts and brood parasites and predators and their prey.An interspecific comparative phylogenetic analysis of escape behavior by hosts and their brood parasites and prey and their predators revealed evidence of consistent behavior when encountering potential parasites or predators.We hypothesize that personality axes such as those ranging from fearfulness to being bold,and from neophobic to curiosity response in brood parasites constitute important components of defense against brood parasitism that reduces the overall risk of parasitism.

Coevolution between Himalayan cuckoos and 2 sympatric Pycnonotidae hosts

Selection due to cuckoo parasitism is responsible for the evolution of anti-parasitism defenses in hosts.Different host species breeding sympatrically with a single parasitic cuckoo may evolve different strategies to reduce the risk of counter cuckoo parasitism,resulting in different interactions between cuckoos and hosts in areas of sympatry.Here,we studied the coevolutionary interactions between Himalayan cuckoos Cuculus saturatus and 2 sympatric and closely related potential hosts belonging to the family Pycnonotidae,the brown-breasted bulbul Pycnonotus xanthorrhous and the collared finchbill Spizixos semitorques.We investigated parasitism rates and nest-site selection(nest height,nest cover,human disturbance,perch height,forest distance,and degree of concealment)related to parasitism risk,nest defense against a cuckoo dummy,and egg rejection against cuckoo model eggs.Bulbuls used specific nest sites that were further away from forests than those of finchbills,and they behaved more aggressively toward cuckoos than finchbills.In contrast,bulbuls possessed moderate egg rejection ability,whereas the finchbill rejected 100%of cuckoo model eggs.We suggest that selection of a nest site away from forests by the bulbul explains the absence of parasitism by Himalayan cuckoos.We suggest that these interspecific differences in nest-site selection and nest defense indicate alternative responses to selection due to cuckoos.