Comparison Of Nest Defense Behaviors Of Three Cavity Nesting Birds Of Sturnidae

Reproduction is an important part of the avian life history,and breeding input and breeding success are affected by multiple negative interactions such as nest site competition,nest usurpation,nest predation,and brood parasitism.The interactions between the birds and its predators,parasites and nest competitors provide a model system for studying co-evolution.Breeding birds need to choose the optimal combination of strategies to maximize their fitness among numerous resource allocations,and among which,nest defense strategy is one of the effective strategies to improve the breeding success.In this study,sympatric breeding of three secondary cavity nesting birds in the Sturnnidae family,namely the crested myna(Acridotheres cristatellus),common myna(Acridotheres tristis)and white-shouldered starling(Sturnus sinensis),were used to compare inter-specific differences in nest defense strategies under the negative interactions of nest-site competition,nest usurpation,nest predation and brood parasitism.The main results and conclusions of the present study are as follows:1.The intensity of human disturbance affected the nest box selection of three cavity nesting birds.The nest box utilization rate of the crested myna in the low human disturbance area was significantly higher than that in the high disturbance area,and by contrast,the nest box utilization rate of the common myna and the white-shouldered starling in the low disturbance area was significantly lower than that in the high disturbance area,indicated that different bird species had different adaptability to different levels of human disturbance,which may be related to different life histories of birds.2.The feather and egg-covering preventing nest usurpation hypotheses suggest that birds can skillfully use nest materials to "cheat" competitors,inducing fear reactions from competitors,thereby preventing competitors from entering the nest.This study found that the long black feathers in the nest could effectively prevent crested mynas usurping the nests,which supported the feather prevent nest usurpation hypothesis;however,the behavior of covering eggs with nest materials could not prevent nest usurpation,and the results did not support the hypothesis that egg-covering behavior may prevent nest usurpation.3.Adding snake sloughs to bird nests can reduce nest predation,but whether the anti-predation function of snake sloughs is applicable to different habitats is unknown.This study found that in the urban area and suburban area,the snake slough in bird nests could effectively reduce the nest predation rate,however,in the tropical forest,the snake slough in the nest did not reduce the nest predation rate,which indicated that the anti-predation function of snake slough may not applicable to all habitats,which could be related to different types of nest predators and predation risk in a given habitat.When facing a "human predator",the flight initial distance(FID)of crested mynas was higher than those of common mynas and white-shouldered starlings in both non-breeding and breeding seasons,which may be due to the long-term capture behavior by local people,which promoted the sensitivity of crested mynas to human activities.When facing three types of predators,namely the squirrels(Tamiops maritimus),snakes(Ptyas mucosus)and sparrowhawks(Accipiter nisus),all three bird species showed strong nest defense behaviors both at the incubation stage and the nestling stage,indicated that at least from a behavioral perspective,three bird species seemed not to be able to distinguish three types of predators.4.Egg size and nestling size cues may play an important role in egg recognition,egg rejection and nestling discrimination of mynas.Results of the egg and nestling experiments showed that the proportion of crested mynas rejecting small eggs and nestling in the nest was higher than that of large eggs and nestlings,which suggested that the egg and nestling recognition mechanism was recognition by discordancy and based on size cues.The dummy recognition experiments found that there were no significant differences in the behavioral responses of the three birds to different specimens both at the incubation stage and the nestling stage,indicated that from a behavioral perspective,three bird species did not seem to be able to distinguish between the parasitic cuckoo(Cuculus canorus)and the adult bird predator sparrowhawk(Streptopelia orientalis)while using dove(Streptopelia orientalis)as a control.5.The intensity of human disturbance affected the breeding success of the three species of birds.The hatching success of the crested myna and the common myna was significantly higher than the breeding success,however,there was no significant difference between the hatching success and breeding success of the white-shouldered starling.The main reason for this difference was that crested mynas and common mynas were highly captured by local people as pet trade.The results of this study indicated that high intensity human interference has a negative impact on the reproduction of crested mynas and common mynas,while the impact on gray backed starlings was minor.To sum up,sympatric breeding birds of three secondary cavity nesting birds in the Sturnnidae family adopted a variety of nest defense strategies to maximize their breeding success.Nest niche differentiation could reduce inter-specific competition and achieve coexistence;adding long black feathers to the nest may prevent nest usurpation while snake slough was added to the nest to prevent nest predation.Capture history by “human predators” prompted birds to sensitize to human activity,which manifested as longer FID.At both egg and nestling stage,all three species of birds showed strong nest defense behavior against nest predators and parasites.Egg and nestling size cues may play a key role in egg recognition and nestling discrimination of mynas.Finally,human disturbance negatively affected breeding success of crested mynas and common mynas,while such effect in white-shouldered starlings may be minor.Future work should focus on more geographical populations and more species in the Sturnnidae family,to better understand intra-and inter-specific differences in nest defense strategies.