Diet Analysis of Five Heron Chicks in South-West Coast in Tainan

• Main Authors: Liao-FanYen, 顏了凡
• Other Authors: Jiang-Ping Wang
• Format: Others
• Language: zh-TW
• Published: 2014
• Online Access: http://ndltd.ncl.edu.tw/handle/94738175730949369617

碩士 === 國立成功大學 === 生命科學系 === 102 === SUMMARY In recent years, Great Egrets (Ardea alba) and Intermediate Egrets (Egretta intermedia) were thought to be winter visitors but found breeding during summer in Taiwan. To protect the feeding habitats of them and other water birds, diet studies during breeding season are necessary. We collected boluses of chicks from Great Egrets, Intermediate Egrets, Little Egrets (Egretta garzetta), Black-crowned Night-Herons (Nycticorax nycticorax), and Cattle Egrets (Bubulcus ibis) from May to July of 2010 in Tainan where located at southwestern Taiwan. We found 2179 individuals in 66 boluses, classified into 11 classes, 20 orders, and 45 families, totally 80 prey items weighing 583.95 g. The most important prey was Chanidae for Great Egrets, Intermediate Egrets, and Little Egrets, but Cichlidae for Black-crowned Night-Herons, Muscidae larvae for Cattle Egrets. Pielou’ s evenness index were lowest in June and Cattle Egrets. The percentage of insects of Cattle Egrets was significantly higher than the others, and the percentage of fish was significantly lower, both by quantity and biomass. Because aquatic food was nearly none, Cattle Egrets should not be waders although they were Ardeidae. INTRODUCTION Tainan is located on southwestern Taiwan where on the route of East Asian-Australasian Flyway. There are lots of fish ponds, salt-pans, and wetlands along the coast of Tainan with plenty of fish, shrimp, and benthos that are able to provide abundant food for water birds. Great Egrets and Intermediate Egrets were thought to be winter visitors before. However, recent observation indicates that they breed during summer in Taiwan (Yen, 1992). Diet studies of sympatric herons in Tainan are necessary, since it gets more and more important to protect the feeding habitats of herons and other water birds. Previous studies show that herons are mainly fed on fish, crustaceans, and insects (Kushland ＆ Hancock, 2005). The food samples were collected from stomachs of adults and boluses of nestlings (Miranda ＆ Collazo, 1997; Montesinos et al., 2008). MATERIALS AND METHODS To avoid killing birds, we decided to analysis the food samples in boluses that vomited from living chicks. The study site were three communal colonies in mangrove, two located at Yanshui Estuary Wetlands, and the other was at Cigu Salt-pans Wetland. Chicks usually vomited boluses when reseachers approached them. We collected samples in day time once a week from May to July of 2010. Boluses were collected from 66 chicks of Great Egrets, Intermediate Egrets, Little Egrets, Black-crowned Night-Herons, and Cattle Egrets. The Samples that preserved in 95% alcohol were classified and recorded by quantity and biomass. The data are analyzed with occurrence frequency, Margalef’ s richness index, Shannon-Wiener index, Pielou’ s evenness index, index of relative importance (IRI), niche breadth, and niche overlap. We also analyzed the differences between months and species by one-way ANOVA. RESULTS AND DISCUSSION From our results, there were 2179 individuals in 66 boluses, classified into 11 classes, 20 orders, and 45 families, totally 80 prey items weighing 583.95 g. The most abundant prey group was insects (46.3% - 93.1%), but fish were dominant by biomass in every month (69.6% - 81.6%). The results of IRI demonstrated that Elopidae, Cichlidae, and Chanidae were the most important prey item in May, June, and July, respectively. Fish were numerically the main prey of Great Egrets, Little Egrets, and Black-crowned Night-Herons, contributing 43.8% - 74.5% of prey items, while insects make up 72.6% and 95.4% of prey eaten by Intermediate Egrets and Cattle Egrets. Insects were also dominant in prey of Cattle Egrets by biomass (80.6%), but other herons were fed mainly on fish (85.7% - 97.1%). According to IRI, the most important prey was Chanidae for Great Egrets, Intermediate Egrets, and Little Egrets, Cichlidae for Black-crowned Night-Herons, and Muscidae larvae for Cattle Egrets. Margalef’ s richness index was highest in June and Cattle Egrets, while Shannon-Wiener index and Pielou’ s evenness index were lowest. Great Egrets had the widest niche breadth, and Black-crowned Night-Herons had the narrowest one. Little Egrets and Black-crowned Night-Herons showed that the highest degree of niche overlap (1.36). Both by quantity and biomass, the proportion of insects of Cattle Egrets was significantly higher than other herons, on the other hand, the proportion of fish was the lowest, no obvious difference between the other four herons. CONCLUSION All the results of this research demonstrated that Great Egrets, Intermediate Egrets, Little Egrets, and Black-crowned Night-Herons were fed mainly on fish, but the most important prey of Cattle Egrets was insects, aquatic food such as fish and shrimp were nearly zero. According to the results, I considered that Cattle Egrets should not be waders, although they are a member of Ardeidae. The results concurred with previous studies mostly, but some prey items including shrimp, frogs and snakes, are few or lack, and the major item of insects predated by Cattle Egrets was Diptera instead of Othoptera . It is that herons are opportunistic, they usually fed on food resources which were the most abundant or easiest to get on local habitates. In this research, samples did not collected during unbreeding season, and no data in another year could be compared, these should be further works to know if herons change their diet between seasons or years. In addition, it needs more researches about environment factors, feeding behavior, and competition of herons to help understand the interaction between diet and factors above.