Host Selection By Common Cuckoos And Defenses Of Two Shrike Hosts Against Cuckoo Parasitism

Obligate brood parasitic birds never build their own nests,but instead lay their eggs in the nests of other host birds,thus transferring the cost of parental care to the host.Nesting birds need to find suitable nest-site for reproduction,while brood parasitic birds need to find suitable nests for parasitism.Brood parasitism reduces the fitness of the host,and thus hosts would evolve anti-parasitic strategies to avoid the costs of nest parasitism,such as attacking parasitic birds that lay eggs and refusing to parasitic eggs.The interactions between avian brood parasites and their hosts provide an easy-to-process and information-rich system for studying behavioral ecology and coevolution.In light of this,host selection by the Common Cuckoo(Cuculus canorus),and defenses of shrike hosts against cuckoo parasitism in the Isabelline Shrike(Lanius isabellinus)and Brown Shrike(L.cristatus)were studied.The main results are as follows:1.Hypotheses on host selection by parasitic cuckoos suggest that the Common Cuckoo may choose its host by imprinting on the habitat(the habitat imprinting hypothesis)or nest-site(the nest-site hypothesis)in which they grow,or on the host species they are reared(the host imprinting hypothesis),or simply by returning their natal site(the natal philopatry hypothesis).Here,we tested mechanisms of host selection by the Common Cuckoo in a multiple host species system composed of five potential hosts breeding within the same habitat,including the Isabelline Shrike,House Sparrow(Passer domesticus),Desert Finch(Rhodopechys obsoleta),Oriental Turtle Dove(Streptopelia orientalis),and Eurasian Collared Dove(S.decaocto).The results showed that the Isabelline Shrike was intensively parasitized by the Common Cuckoo with a parasitism rate of 26.9% in 2018-2020 and evolved egg recognition ability to reject parasitic eggs with a rejection rate of 62.2% to non-mimetic model eggs.No cuckoo eggs were found in nests of the other four potential hosts,and egg recognition and dummy experiments showed that these potential hosts did not have the ability to recognize foreign eggs and even did not attack the cuckoo dummy.Our results did support the host imprinting hypothesis that cuckoos may imprint on the host species they are reared.2.The Red-backed Shrike(Lanius collurio)in Europe shows a high antiparasitism ability,and the Bull-headed Shrike(L.bucephalus)in Japan has a moderate anti-parasitism ability.The anti-parasitic ability in the Lanius bird species,especially egg recognition ability may have a genetic basis.Therefore,nest defense and egg recognition of Isabelline Shrikes from Northwest China(close to Europe,and more closely related to the Red-backed Shrike)and Brown Shrikes from Northeast China(close to Japan,and more closely related to the Bull-headed Shrike)were compared.Our results showed that the attack rate of Brown Shrike in Northeast China on Common Cuckoo dummies was significantly less intensive than that of Isabelline Shrike in Northwest China.The Brown Shrike(no cuckoo parasitism found)was able to recognize and reject the non-mimetic model eggs up to 100%,while the Isabelline Shrike(parasitized by the Common Cuckoo with a rate of 63.3%)rejected only 50%of the non-mimetic model eggs.This study showed that nest defense and egg recognition in Lanius shrikes varied with different species,regions and habitats,suggesting that nest defense and egg recognition ability may be affected by various behavioral and ecological factors.3.To test whether the host may adjust its anti-parasitic strategies according to the risk of cuckoo parasitism,especially in our case,when parasitic cuckoos and their hosts breed at a mis-matched time with each other.In our study area,the Isabelline Shrike starts breeding in early April each year while the migratory Common Cuckoo starts its egg-laying in late May.The results showed that,compared with the time period before the arrival of cuckoos,Isabelline Shrikes showed higher attacks to the Common Cuckoo dummy after the arrival of cuckoos.However,there was no significant difference in egg rejection rate before and after the arrival of cuckoos.The present study showed that Isabelline Shrikes may adjust its nest defense behavior,but not egg recognition,according to the risk of cuckoo parasitism.Innovation:1.The host selection mechanisms by Common Cuckoos has not been unanimo usly concluded.By excluding the possibility of other hypotheses,this study indirectly supported the host imprinting hypothesis that cuckoos may imprint on the host species they are reared.2.Previous work suggested that the ability of shrikes to recognize alien eggs has a genetic basis.However,this study showed that although both Isabelline Shrikes and Brown Shrikes have the ability to recognize alien eggs,the strength of egg recognition ability is not directly related to the phylogeographic and geographical distance.This provided a basis for understanding the genetic evolution of egg recognition ability in Lanius shrikes.3.This paper compared the anti-parasitic strategies,e.g.,nest defense and egg recognition,of Isabelline Shrikes before and after the arrival of the migratory Common Cuckoos and indicated that the Isabelline Shrike may adjust its nest defense strategy in a short time period based on the risk of cuckoo parasitism,suggesting breeding ahead of parasitic cuckoo arrival by hosts would be a highly efficient anti-parasitic strategy.