| Summary: | 碩士 === 國立臺灣大學 === 森林環境暨資源學研究所 === 97 === Hatching asynchrony is usually caused by parents starting incubation before clutch completion. By producing age-size hierarchy between nestlings, later-hatched nestlings may suffer from delayed development compared with early-hatched nestlings. Furthermore, being disadvantaged due to food resource competition which is caused by their smaller size may results in them fledging with lighter body mass as well as higher mortality. Each group member in joint-nesting system has similar reproductive probability. Under this situation, females of different hierarchy may adopt different laying strategies to increase individual fitness. I examined how female adjust their laying behavior in the cooperative breeding birds, joint nesting Taiwan Yuhinas (Yuhina brunneiceps). I found that the number of eggs before nocturnal incubation was correlated with the number of early-hatched nestlings, and the number of early-hatched nestlings was also positively correlated with the number of heavy nestlings. It suggested that eggs which incubated earlier would hatch earlier, and these nestlings could be advantageous in terms of body mass is concerned. 72% of nestlings retain the advantage of body mass until they fledge. The average precipitation in the egg-laying period of the nests that nocturnal incubation start after egg completion was higher than nests that nocturnal incubation start before egg completion. The precipitation may be the key factor that influence female’s decision. Female didn’t pay extra energy during raining days, and they generally laid less eggs and have reduced competing intensity that can’t successfully prevent other female laying eggs, which causes hatching synchronously. As a result, they produced less nestlings with heavier body mass, and higher survival rate than nestlings that hatched asynchronously. Competition behavior causes hatching asynchrony (HA), even though the mortality of nestlings was higher in HA but can produce more nestlings than in hatching synchrony (HS).
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