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Characteristics of breeding bird communities in the Mt. Halla
Distribution and abundance of birds have close relationship with the characteristics of habitats. Especially in breeding season, stable place to build up nests, food items for offspring and existence of available mates are important factors affecting successful reproduction. Therefore, breeding bird community varies according to the specific breeding habits for each species and environmental characteristics. Mt. Halla is located center of Jeju island and consists of different vegetation according to the elevation. In lowland, Seonheul with 100m elevation has wetlands and evergreen broad leaved forests lies while mixed forest and Korean fir (Abies koreana) community in higher elevation. Mixed forest in Mt. halla was designated as gene conservation forest by Korea Forest Service because of its is high quality of preservation and is located in 1,200m elevation. Abies koreana forest in 1,300m elevation consists of mainly Korean fir (Abies koreana) that is endemic species in Korea, but is susceptable to wind and soil quality because of its shallow and spreading root system and recently being damaged due to the climate change. To investigate breeding bird community in Mt. Halla, bird census was conducted from April to August, 2011 to 2013. A total of 17 species which consists of 17 species in Seonheul, 9 species in the mixed forest, and 7 species in Abies koreana forest were observed during the study period. Community indices such as species diversity, evenness, and richness index were almost consistent yearly but changed according to the study sites. In Seonheul, diversity and richness index were much higher than in others. Mixed forest had slightly higher diversity and richness index than Abies koreana forest. According to the correspondence analysis(CA), bird community in Seonheul showed distinctive difference with that in mixed forest and Abies koreana forest. Similarity in bird community was higher in Seonheul, compared to that in mixed forest and Abies koreana forest. Bird species and individuals were more abundant in Seonheul. Nesting guilds were classified as ground, bush, canopy, hole, brood parasite, and artificial structures. All sites had the same composition of nesting guild across all three years. In Seonheul, variability of nesting guilds was greatest including ground, brood parasite, and artificial structures which were not observed in the other sites. In Seonheul, the number of species that bred in canopy was largest and in mixed forest and Abies koreana forest, the number of species that bred in hole was the greatest indicating most of the bird species used tall trees as nesting sites. The number of individuals in the entire sites tended to decrease yearly. The number of individuals that bred in canopy was greatest in Seonheul but decreased across years as well as in bush and hole. In Abies koreana forest, the number of hole nesters and the birds breed in canopy tended to decrease from 2011 to 2013. Foraging guilds were categorized into ground, bush, canopy, and air. The number of species consisiting foraging guilds was the same from 2011 to 2013 throughout study sites. The most preferred foraging guild was ground in Seonheul(7 species), while canopy in the mixed forest(6 species) and Abies koreana forest(5 speices). Also, the species foraged in the air, the barn swallow and the japanese paradise flycatcher were observed only in Seonheul. The average number of individuals that foraged in canopy, 50 individuals, was greatest in all the sites across all three years and the following was in ground consisting 32 individuals. The number of individuals that foraged in canopy which mainly comprised of great tits, varied tits,and japanese white-eyes, tended to decrease in Seonheul, 80 to 44 and Abies koreana forest, 46 to 24 from 2011 to 2013, except mixed forest in which the number of these increased. In Seonheul, the number of individuals foraged in air tended to increase because of the sudden increment in the number of barn swallows: 24 individuals in 2011 to 52 in 2013 as shown in the number of individuals nested in artificial structures. Since Seonheul provides diverse habitats such as wetlands, various vegetation structures and high coverage of tree layer, many different bird species inhabit. Barn swallows and japanese paradise flycatchers which forage for these flying in the air were observed in Seonheul and it seems that this is because the environment seems suitable for insects. Generally tall trees were most favored as nesting and foraging place in all the study sites. For example, the japanese paradise flycatcher and the fairy pitta which favor dark area seemed to have bred in Seonheul, because of the high coverage of tall trees blocked sunlight enough. Also, Family Paridae such as great tits and varied tits nested in holes in tall trees. Furthermore, Family Paridae, japanese white-eyes and brown-eared bulbuls foraged for insects and fruits on tall trees, occupying the largest portion in terms of the number of individuals in foraging guilds. Despite this high usage of tall trees, these are now being lost in Seonheul and Abies koreana forest. Especially in Seonheul, Pinus thunbergii that infected by Bursaphelenchus xylophilus are logged out since October, 2013, deteriorating habitat quality. Furthermore in Abies koreana forest, almost half of the Abies koreana has died and 20.7% of them died since 2011 mainly due to the climate change, according to the Mt. Halla research institute. Such environmental change might have caused decrease in the number of individuals that rely on the tall trees for both nesting and foraging place such as white-backed woodpeckers, great tits, coal tits, varied tits and brown-eared bulbuls. From 2011 to 2013, average daily temperature increased rapidly and average maximum temperature in March, right before egg laying period, increased by 4℃ compared to that in 2011. It has been reported that abrupt change in early breeding period could result in decreased reproduction success rate because of mismatch of time between hatching period and time when caterpillar abundance is high enough to feed nestlings. Therefore, the average temperature increase also might have caused decreased individual number of the species in great tits and varied tits.
