金門栗喉蜂虎種內托卵寄生與棄蛋行為

Abstract

寄生者(parasite)透過種內托卵寄生(intraspecific brood parasitism)在其他個體巢中下蛋減少親代照顧(parental care)，提升親代投資效益。有些鳥類中的宿主(host)可以透過棄蛋行為(egg-rejection)抵抗種內托卵寄生，減少種內托卵寄生對親代投資的影響。每年繁殖季可以在金門栗喉蜂虎(Merops philippinus)巢洞外發現30-90顆蛋殼完整的棄蛋(abandoned egg)，人工孵育結果顯示超過1/2的棄蛋已授精且具有孵化能力。行為觀察也指出栗喉蜂虎有種內托卵寄生行為。為了釐清栗喉蜂虎宿主的棄蛋行為如何影響種內托卵寄生，本研究分成兩個部分，第一部分於2019年在金門地區選取5個樣區進行人為托卵寄生試驗，分別在宿主下蛋前後放入人工假蛋，透過繁殖監測記錄假蛋狀態。第二部分針對棄蛋、巢內蛋及離巢前幼鳥，分析不同繁殖階段子代與親鳥的親緣關係。第一部分結果顯示，遭移除的假蛋皆在宿主下蛋前(n=31)，下蛋後的假蛋都被宿主接受並持續孵育(n=50)，然而部分在下蛋前3日內試驗的假蛋被接受(n=3)。第二部分親緣分析指出，大部分棄蛋與親鳥無親緣關係(n=7)，應是宿主的棄蛋行為所致。少數具有親緣關係的案例(n=1)可能是移蛋行為(egg trasfer)的結果。3巢巢內蛋的結果顯示，在有棄蛋出現的情況下，巢內仍有多達1/3非親生蛋；高於平均窩卵數的宿主也持續孵育巢內蛋。離巢前幼鳥中，巢中親生幼鳥最多5隻，非親生幼鳥最多3隻；此外，也有1巢2隻幼鳥全為非親生的案例。綜合上述，宿主的棄蛋行為能有效移除下蛋前的寄生蛋；下蛋後，宿主會接受寄生子代，栗喉蜂虎採取種內托卵寄生繁殖策略可以產生子代。

Bird parasites of intraspecific brood parasitism (IBP) reduced parental care by laying eggs in others nest. By contrast, Some avian host took actions against IBP through egg-rejection. Abandoned eggs was common phenomenon in Blue-tailed Bee-eaters(Merops philippinus) breeding in Kinmen. Around 30-90 abandoned eggs could be found in breeding colonies each year, and over one half of abandoned eggs were fertilized and able to hatch. Evidences of IBP in blue-tailed bee-eaters were confirmed through behavioral observation. To examine how egg-rejection by host affected the behavior of IBP parasites, this study was divided into 2 sections. First section, I conducted artificial egg experiment in 5 sampling colonies in 2019. Artificial eggs were added into cavities both before and after host laying, and the status of eggs were monitored. Second section, we analyzed kinship of abandoned eggs, eggs in nest, and fledgling, respectively, with their putative parents. In first section, Artificial eggs were rejected only before hosts lay the first egg (n=31). While after hosts laid their first egg, they tolerated parasitic eggs remain in the nest and hatched as true eggs (n=50). However, some eggs entered cavities within 3 days would also keep and incubate by hosts (n=3). Results of second section showed that most abandoned eggs were non-related to parents (n=7), which may come from hosts’ egg-rejection against intraspecific brood parasitism. We found egg transfer IBP might contribute to the presence of abandon eggs related to parents (n=1). Kinship of eggs in nest from 3 nests revealed that hosts still accepted eggs in clutch while there were abandoned eggs and 1/3 of offspring were non-related. Besides, nests with exceeded clutch size were also incubated. Among kinship of fledglings, up to 3 non-related fledglings in one nest.on the other hands, 5 related fledgling remained. In conclusion, host can only reject parasitic eggs before laying. Since parasitic eggs accepted, IBP is successful strategies able to produce offsprings in Blue-tailed Bee-eater.