Nest Site Selection For Five Common Birds And Their Coexistence In An Urban Habitat

Compared with the natural environment,the urbanized habitat is a new habitat for many birds.In order to succeed in natural selection,birds must adjust their reproductive strategies and adapt to the urbanized habitat.Current researches focus on nest site selection at the individual level.Urban bird competition mainly focuses on the competitive relationship between invasive and native species,dominant and subordinate species,and two or three related species.Understanding the impact of urbanization on birds and the competitive relationship has important implications for the conservation and management of wildlife in urban ecosystems.In this study,we undertook a systematic study to quantify nests in all species of birds in an urbanizing area of Nanchang University in Nanchang,China.We used Spearman correlation analysis,the one-way analysis of variance(ANOVA)test and Duncan's new multiple range test,principal component analysis,logistic regression to(1)to identify where the birds nest and what the factors are affecting their nest site selection,and(2)confirm the niche differentiation of bird species sustains their coexistence in urban environments.The results are as follows:(1)A total of 373 nests were detected in surveys including 350 nests of 16 bird species and 23 unrecognized nests.The largest number of nests belonged to light-vented bulbul's(Pycnonotus sinensis)(n=216),which accounted for 58.91%of the total.The most nests were found in the tree of artificial green belts(n=350),93.83%of the total.There were 360 nests on the tree,accounting for 96.51%of all nests.Only 13 nests are on the building,accounting for 3.49%of all nests.Light-vented bulbul and Chinese blackbird(Turdus Mandarinus)had obvious preferences for nesting tree.Light-vented bulbul preferred to nest in Camellia japonica,while Chinese blackbird preferred to nest in Cinnamomum camphora.Differently,scaly-breasted munia,spotted dove and grey-capped greenfinch showed no apparently preference to any special tree species.(2)In a comparison of environmental and nest characteristics among five species of birds,the ANOVA and Duncan's new multiple range test showed significant difference among 9 environmental and 4 nest characteristics.For BIPP,there were no significant difference among five species.(3)The PCA performed on the nest site characteristics of nest selection variables yielded three principal components.First three principal components accounted for60.348%of the total variance.For nest niche distribution analyses,in the first component,an extensive overlap among spotted dove and the other four species was obvious.Conversely,there was no overlap between light-vented bulbul and Chinese blackbird.The niches used by the spotted dove and Chinese blackbird were much wider than those used by the other species.The overlap area was the largest between scaly-breasted munia and grey-capped greenfinch,which indicated the similar nest niches between these two species.However,in the second component,all five species were overlapped.(4)We identified one of the best nest site selection models(top-rank model,?AICC=0)among the five species,respectively.The model nest site height+minimum spacing of intraspecific nest+minimum spacing of interspecific nest+distance to road+distance to water sources(w_i=0.708,AUC=0.959)was the best model of light-vented bulbul;the model nest site height+ground diameter+concealment+minimum spacing of intraspecific nest+minimum spacing of interspecific nest+distance to water sources(w_i=0.331,AUC=0.973)was the best model of Chinese blackbird;the model ground diameter+minimum spacing of interspecific nest+distance to road](w_i=0.665,AUC=0.737)was the best model of scaly-breasted munia;the model ground diameter+percent canopy cover+minimum spacing of intraspecific nest+minimum spacing of interspecific nest+distance to road(w_i=0.542,AUC=0.779)was the best model of spotted dove;the model nest site height+ground diameter+percent canopy cover+concealment+minimum spacing of intraspecific nest(w_i=0.265,AUC=0.765)was the best model of grey-capped greenfinch.Birds'breeding success relies on the trade-off between the benefit and the expense of specific stresses from habitats.Birds could get more resources from green belts between buildings and secondary forests,including large amounts of human food waste,fruits and flowers of ornamental plants,urban protection of birds from other predators who cannot survive in urban environments,and relatively less human interference.The nest site selection of birds is also affected by the life habit of predators.Many birds had improved their adaptability to nest site selection for reducing predation.Different species choose different nesting strategies to reduce the reproductive loss of prey.Nesting in trees with higher nest height or concealment or closer to the road could reduce the risk of predation when birds reproduce in the green belt,which is conducive to the successful reproduction of birds.In cities,competition among birds can affect the utilization and distribution of resources in the environment.Competitive pressures among species can lead to preferences of different birds for different environmental characteristics.Light-vented bulbul and Chinese blackbird had less competition pressure,and they had obvious preference for tree species;while scaly-breasted munia,spotted dove and grey-capped greenfinch had greater competition pressure,they would nest on more tree species to reduce competition.Competition among different birds leads to niche differentiation.The degree of competition pressure reflects the strategy of nest site selection of different birds.