Responses Of Bird Guilds And Similarity Of Their Species Composition To Habitat Fragmentation On Land-Bridge Islands In The Thousand Island Lake,China

To explore the sensitivities of avian communities to habitat fragmentation and their seasonal changes, and to understand responses of the bird guilds to habitat fragmentation and their seasonal changes, we sampled41land-bridge islands to encompass as much as variation in area as possible in the Thousand Island Lake in Zhejiang province, China. On these islands, we surveyed avian community compositions using line transect during the breeding (April to June) and winter (November to January) seasons annually from April2009to January2012. We assigned the bird species to different bird guilds according to the dietary types, foraging strata and migratory status. We then estimated the sensitivities of the bird guilds to fragmentation, seasonal changes and correlations between the similarities of the bird guilds and the island variables. The results showed that:(1) Sensitivities of some bird guilds, such as omnivorous and resident birds, to fragmentation were different between breeding and winter seasons. However, the others that included insectivorous birds, canopy birds, understory birds and migrant birds were not.(2) Different guilds displayed different sensitivities to fragmentation in the same season. Understory birds were more sensitive to fragmentation than canopy birds in both the breeding and winter seasons. Insectivorous and omnivorous birds showed no difference in their sensitivities to fragmentation in the breeding season, In winter, however, omnivorous birds were more sensitive to fragmentation than insectivorous birds. Resident and migrant birds also showed no differences in their sensitivities to fragmentation in the breeding season, whereas resident birds were more sensitive to fragmentation than migrant birds in winter season.(3) Similarities of the avian communities were negatively correlated with island area and habitat richness in both the breeding and winter seasons. Similarities of year-round avian communities were negatively correlated with island area.(4) Similarities of different bird guilds responded differently to the island variables in the same season. Similarities of insectivorous and omnivorous birds showed different responses to the island variables in both the breeding season and winter, so did the resident and migrant birds. Besides, canopy and understory birds didn’t respond differently in both seasons.(5) Similarities of some guilds responded differently to the island variables in different seasons. Similarities of insectivorous birds showed no correlations with the island variables in the breeding season, but were negatively correlated with the island area and habitat richness. Similarity of omnivorous birds showed a weak and negative correlation with the island isolation in the breeding season, but was not correlated with the island variables in winter. Resident birds were negatively correlated with island isolation in the breeding season and were negatively correlated with island area and habitat richness in winter. Canopy birds, understory birds and migrant birds showed no correlations with island variables in both seasons.Responses of bird guilds and similarity of their species composition to habitat fragmentation on land-bridge islands in the Thousand Island Lake were different from the responses to terrestrial fragmentation. Our research enriched the theory on functional traits and dynamic changes of avian communities, thus it provided more specific management strategies in conservation for natural reserves.