Nestling Diet, Nest Site Selection and Nest Success of the Fairy Pitta (Pitta nympha) in Taiwan
|Keywords:||陸域遷徙鳥種;食物;蚯蚓;錄影;繁殖成功;地面巢天敵掠食;訊息理論法;棲地復原;回播;調查;migratory landbirds;food;earthworm;videotaping;reproductive success;ground-nest predation;information-theoretic approach;habitat restoration;playback;census||Issue Date:||2008||Abstract:||
亞洲地區的熱帶與亞熱帶原生森林此刻正快速消失中。繁殖於東亞，並於婆羅洲度冬的低海拔森林鳥種 - 八色鳥 (Pitta nympha) 為一資訊有限的全球性受脅(vulnerable)鳥種。由於嚴重的棲地喪失，八色鳥在其繁殖區、度冬區以及遷徙路徑上所需適宜棲地的面積，可能已不足以支撐其族群。雖然亟需提高對八色鳥保育現況的關注，但目前仍缺乏較為縝密透徹的研究，故有必要針對八色鳥進行多方面的研究，累積足夠的生態與生物學知識，以作為研擬其保育及經營管理措施的基礎。本研究首先針對生性隱密的八色鳥，提出一種於生殖季利用回播叫聲調查其出現與否及數量的有效調查方式；而後報導藉助上述調查方式，於台灣中西部的低海拔丘陵地研究八色鳥雛鳥食性及植被結構與竹林密度對其巢位選擇及繁殖成功率影響的研究成果。 利用回播叫聲來調查八色鳥出現與否及數量的有效性評估試驗於2001年四月底至五月底進行。八色鳥對回播的反應相當快速，94%的回應出現在5 min之內。。由於無論是偵測到八色鳥的調查點比例及各調查點平均記錄數量，均在使用回播後增加，故回播可明顯地增加偵測到八色鳥的可能性。另偵測到八色鳥的調查點的比例及各調查點平均記錄數量，在五月上旬顯著地高於五月中旬及下旬，在一日中的不同時段(清晨、中午及下午)，在調查結果上並無顯著差異。試驗結果顯示回播可相當程度地增加八色鳥的偵測度，另在一調查點回播5 min已足夠。此外，針對八色鳥族群調查，最好於繁殖季將開始及繁殖季初期進行，而如能於同一地點進行最少2次的調查，應可高度確定該地點是否有八色鳥出現。 八色鳥雛鳥食性研究來自於8巢於2000 - 2002年間拍攝的親鳥育雛影像資料的分析。蚯蚓在所有觀察巢中都是最重要的食物種類，且在所有餵食次數中的平均出現率超過73%。親鳥每次回巢餵食雛鳥通常攜帶1-3條食物單元(items)，食物長度則常在2-10 cm之間。依據1巢完整的觀察，育雛期間親鳥餵食巢中雛鳥總次數估計在900-1000次。此外，上述在乾季繁殖的鳥巢的蚯蚓出現率有隨雛鳥日齡而漸減的現象，推測可能與乾季期間蚯蚓數量下降或較不容易獲得有關。 植被結構與竹林密度對八色鳥巢位選擇與繁殖成功率影響的研究於2004-2006年的繁殖季，在一以竹林(Dentrocalamus latiflorus)為優勢植被的丘陵地進行。繁殖資料透過監測鳥巢的繁殖過程、量化繁殖結果與決定繁殖失敗的原因來獲得。巢位與其成對隨機對應點(n = 65 pairs)，以及繁殖成功(指鳥巢至少有1隻雛鳥成功離巢，n = 32)與繁殖失敗(n = 32)巢位間的棲地環境，以binary logistic regression進行分析。此外，利用Akaike’s Information Criterion (AICc) 及模式平均，在彼此互相競爭的模式中，推導出最受支持的模式與進行各因子相對重要性的計算。八色鳥傾向選擇樹冠覆蓋濃密[相對重要性值(RI) = 0.99]、樹木歧異度高(RI = 0.87)、巢邊1m半徑內灌木密度較低(RI = 0.75)、巢邊5m半徑內小灌木密度適中(RI = 0.79)及離最近樹木距離適中的地點築巢(RI = 0.57)。另巢若築在接近或遠離最近樹木基部(RI = 0.74)、有較高巢上覆蓋度(RI = 0.63)、巢下方坡度較陡(RI = 0.48)及位於較難接近的地點(RI = 0.35)，則其繁殖成功率較高。因此，在5個與最佳巢位選擇模式有關的棲地因子中，僅1項與繁殖成功率有關，且呈現相反的關係。唯雖然偏好的棲地特徵與繁殖成功率無明顯相關，八色鳥卻鮮少築巢於與偏好棲地差異甚具的地點。此外，雖然竹林密度並未包含於最佳巢位選擇模式中，但因它與樹木歧異度顯著負相關，故八色鳥仍有築巢於竹林密度較低地點的傾向。因此，建議經營管理者透過保護殘存的闊葉樹林，及沿著地勢變化較大的溪谷兩側復原與原生闊葉林棲地類似的環境，來擴大適合的八色鳥築巢的棲地面積。
Tropical and subtropical Asia is currently confronting particularly severe forest conversion pressure. The vulnerable Fairy Pitta (Pitta nympha) is an understudied passerine which breeds in the low-elevation forests of eastern Asia and probably winters on Borneo. Because of severe habitat loss, suitable habitat within its breeding and wintering ranges as well as on its migration routes might not be sufficient to maintain its population. In addition, there are no published intensive studies on any migrating pitta species. Thus, there is an urgent need to establish knowledge of all aspects of its ecology and biology and then to propose suitable management measures to conserve this threatened species. In this dissertation, I firstly propose an effective method using playback to census this elusive species during its early breeding season. Followed by studies on its nestling diet, nest site selection and nesting success in west-central Taiwan. The effectiveness of using playback of recorded calls to census the presence and abundance of the Fairy Pitta was evaluated from late April to May 2001. The response of Fairy Pittas to playback was rapid; with 94% occurring in the first 5 min. Playback substantially increases the likelihood of detecting Fairy Pittas. Both the number of stations at which pittas were detected and the number of pittas detected per station increased with the use of playback. In addition, both the number of stations that detected pittas and the number of pittas detected per station were significantly higher in early than mid- and late May, but did not differ at different times of the day (early morning, noon, and afternoon). Our results indicate that playback considerably increased detectability, and 5 min of playback at a station is sufficient. However, it is important to census the Fairy Pitta population during the pre- to early-nesting period, and this should be carried out at least twice to ensure a high certainty of determining the presence or absence of Fairy Pittas at a station. The nestling diet of Fairy Pitta was studied by videotaping eight broods from 2000 to 2002. Adults usually brought 1-3 items at each feeding visit to nestlings, and the prey sizes were usually 2-10 cm in length. The total number of food provisionings to provide food for nestlings was estimated to be around 900-1000 based on a brood observed for the entire nestling period. Earthworms were the most important food item for all broods and occurred in more than 73% of the adult’s feeding visits. However, the occurrences of earthworms as food decreased with nestling age in a brood which was observed during drought conditions, possibly due to a decline in earthworm abundances during this dry period. Nest site selection and nesting success of Fairy Pitta were studied in a hilly area predominantly planted with bamboo (Dentrocalamus latiflorus) over three breeding seasons from 2004 to 2006. I and field assistants tracked success of all nests, quantified nest outcomes and determined possible causes of nest failures. Using binary logistic regression, I compared nesting habitats between each nest site and paired random location (n = 65 pairs), and between successful (i.e., a nest that successfully fledged at least one offspring, n = 32) and depredated nests (n = 32). Akaike’s Information Criterion (AICc) and model averaging were used to make inference about the weighted support for the importance of individual habitat variables through comparison of sets of competing models. Fairy Pitta chose to nest in areas with increased canopy cover (relative importance, RI = 0.99) and a diversity of trees (RI = 0.87) coupled with decreased shrub density immediately around the nest (RI = 0.75) and moderate small shrub density near the nest (RI = 0.79) and situated at a moderate distance from the nearest tree (RI = 0.57). Nests built in places that were closer to or farther form the base of the nearest tree (RI = 0.74), with higher overhead cover (RI = 0.63), with a steeper downward slope (RI = 0.48) and with greater difficulty to access (RI = 0.35) were more successful. Thus, of the five habitat characteristics that were associated with nest site selection, only one was related to nesting success with an inverse relationship. Although most habitat characteristics preferred did not positively relate to nest success, Fairy Pitta rarely located their nests in areas without these characteristics. Also, although bamboo density was not included in the best nest site selection models, it did significantly negatively correlate with the diversity of trees. Therefore, I recommend that managers protect remaining broadleaf forests and restore similar habitat in areas of rough terrain, usually found along valleys, to enlarge areas of suitable habitat.
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