灰頭鷦鶯鳴唱聲的地理變異

Abstract

灰頭鷦鶯(Prinia flaviventris)是臺灣平原及丘陵地區常見的留鳥，主要棲息在農耕地及草生地。本研究分析了來自臺灣本島各地150隻灰頭鷦鶯的鳴唱聲，以探討不同類型的歌曲特徵在不同地理尺度下的地理變異，並探討變異形成的可能機制。歌曲的物理性質部分，與歌曲頻率相關的特徵，如最高頻率或頻率寬度，在不同地理尺度下有不同的變異趨勢。在不同區域間，頻率相關特徵與區域繁殖季平均溫度呈正相關。但在部分地理區內，頻率相關特徵卻與地區繁殖季平均溫度呈負相關，並與相對溼度呈正相關，此地理區內的變異趨勢應與不同微氣候條件下聲音的傳遞效率有關。本研究並以取樣點與最近都市及道路的距離作為間接衡量指標，檢驗是否在較都市化的環境下，頻率相關特徵是否會為避免人為的低頻噪音干擾而提高，結果此現象並不成立。與時間相關的特徵，如歌曲長度、歌曲內的音符數或單位時間內被唱出的音符數，呈現北-西南-東南三個區域間的變異：北部的歌曲最長、歌曲內音符數最多且單位時間內被唱出的音符數最多；東部的歌曲最短、歌曲內音符數最少且單位時間內被唱出的音符數也最少；西部地區的特徵則介於北、東兩區之間。唯本研究並未對此變異趨勢的可能成因進行測試。歌曲內的音符組成部分，總共發現22種音符類型，音符組成在東北(宜蘭)、東南(花東)及西部三個區域之間有明顯差異，應與區域間山脈造成的地理阻隔有關。區域內的音符組成大致符合中性假說的預測，顯示區域內不同音符類型出現頻度的差異可能主要由逢機的文化突變(cultural mutation)和文化漂變(cultural drift)所造成。

The Yellow-bellied Prinia (Prinia flaviventris) is a common resident bird species in the lowlands and foothills in Taiwan. We analyzed the songs of 150 Yellow-bellied Prinia recorded throughout the island of Taiwan to reveal the patterns of geographic variations in different song characters and the potential mechanisms that led to such patterns. In the physical characters of the song, we found the frequency-related characters had different trends of variations at different geographic scales. At the inter-population scale, we found these characters were positively correlated with the regional mean of the mean temperature in the breeding season. At the intra-population scale, we found these characters were negatively correlated with the mean temperature in the breeding season and positively correlated with the relative humidity in some populations. These within-population associations should be the results of differential transmission efficiencies in different micro-climatic conditions. We used the distances to the nearest cities and roads as indirect indices of human disturbances to test if birds sing songs with a higher frequency near cities or roads to avoid the human-produced low-frequency noises. The hypothesis was not supported. The time-related characters varied among the northern, the southwest, and the southeast populations at inter-population scale, but we did not test any candidate hypothesis about the process of this pattern. The note types varied among the western, the northeast, and the southeast populations, which reflected the isolating effects of mountain ranges between populations. The within-population variations in the relative frequency of each note type followed the predictions of the neutral hypothesis, suggesting that these variations were the results of cultural mutation and cultural drift.