摘要
隨著人口增長、都市化在世界各地快速蔓延、嚴重影響全世界的生態系統。常見的問題為整體生態多樣性的降低及少數能適應都市物種的茁壯。而都市化所帶來的危害(包含人為干擾、去森林化、光害及噪音汙染等等) 不僅會影響生物集合 (assemblages) 、更會影響仍棲息在當地的物種、改變其生活的方式及習慣。很多鳥類種類為一常見的都市風景分布於全世界包含台灣。根據文獻、由於大部分鳥類仰賴聲音進行溝通、因此對於人類的干擾、包含都市化、噪音汙染的影響非常敏感。許多研究指出噪音對於鳥類的溝通有顯著的影響、但關於噪音對鳥類其他方面生活型態的影響並未被完整的研究。其中一個例子為鳥類的抗掠食行為。動物於掠食及抗掠食的指標為警戒距離 (alert distance - AD) 及驚飛距離 (flight initiation distance - FID)、前者為動物會對掠食者的侵入發出警戒的距離、而後者為掠食者接近獵物時造成獵物開始逃跑的距離。
本研究探討噪音及其他環境因素對都會區中三種鳥類、麻雀 (Passer montanus) 、家八哥 (Acridotheres tristis) 、 及珠頸斑鳩 (Streptopelia chinensis) 抗掠食行為的影響。為考量不同的條件、本研究分別在台南市東區的四個公園及五個位於安平區的公園蒐集樣本。相較於安平區、東區人口較多、都市化程度較高、相對應也產生較多噪音污染。本研究於每次採樣前在每個公園的中心位置量測噪音級別。量測資料顯示位於安平的五個公園相對於其他四個位於東區的公園呈現較低的噪音級。本研究使用Google Earth來估算樹木覆蓋率、而觀察結果顯示抗掠食行為的指標與樹木覆蓋率呈現正相關趨勢。三種鳥類的AD及FID皆被測量、測量的方法為採集者接近待測鳥直到該鳥警戒、而待測鳥遭受危機後飛行的距離(DF)也同時被量測。AD與FID的差異、定義為緩冲距離(BD) 、也量化成另一項評估危機的指標供本研究使用。
麻雀的FID在東區所量測到的結果相較於在安平區測到的結果皆明顯低了許多。雖然觀察結果顯示棲息於更加都市化地區的鳥類對於人類的活動及其所潛藏的危機相較於較不都市化地區更加不敏感、但噪音級在觀察中並未與抗掠食行為的指標有顯著的正相關。可能原因為本實驗的設計並未精準的量測到每隻鳥在觀察者接近時所接收到聲音的噪音級。族群大小、季節、鳥類以及樹木覆蓋率在本研究中是影響鳥類的重要指標。在樹木覆蓋率較高的公園中、各種鳥類的AD、FID以及警覺後飛行的距離相較於樹木覆蓋率低的公園較低的趨勢。另外、對於麻雀、在樹木覆蓋率低的公園、其他因素的影響如族群大小與季節對於AD、FID以及警覺後飛行的距離皆有較強的影響。
即使在都市化的地區、都市化程度的不同對於鳥類的干擾仍有差異。因此、在不同的公園所採集到的鳥類抗掠食行為與對人類活動的敏感程度皆有所變異。若要將噪音汙染對抗掠食行為影響量化、在採樣當下所量測到的噪音級需與實驗前所測量的環境噪音級相減。此外、本研究發現在樹木覆蓋率低的探測點所控制的因素、如人為干擾及噪音汙染、對鳥類造成的影響能夠被更顯著的觀察出來。樹木覆蓋率對於小型鳥類(如麻雀)的危險感知有顯著的影響、因此弱化了其他因素(如季節、族群大小及噪音等) 對飛行行為的影響。未來期望能在樹木覆蓋率低的探測點測量聲音對鳥類飛行行為的影響、如此得以最大化排除聲音以外的因素(如樹木覆蓋率)的影響。
關鍵字：警戒距離、反掠食者行為、逃避行為、驚飛距離、噪音污染、都市化

ABSTRACT
Urbanization is an ever-increasing developmental process and disturbing force affecting global ecosystems. This process can occur at both local scales and/or larger regional scales; typically, urbanization that covers a larger geographical area has much more negative impact on affected ecosystems compared to more localized urbanization only impacting a relatively small area. A common finding in and around urbanized areas is a decrease in overall biodiversity and an increase in abundance of only a few successful urban dwelling species. Not only can factors associated with urbanization (e.g., human disturbance, deforestation, light pollution, sound pollution, etc.) affect both which species are present in an area and the relative abundances of these species, but they also can affect the behaviors of the species still present in these areas. Many common bird species are an everyday sight in cities around the world, including those in Taiwan. Birds have been shown to be particularly susceptible to one certain aspect of urbanization and subsequent human disturbance, sound pollution, due to the vocal nature of communication in most bird species. While sound level has been demonstrated in many studies to have clear effects on communication in bird species, the effects of sound pollution on other aspects of bird behavior have been studied but not as thoroughly. An example of such behavior is anti-predatory behavior, or the range of responses an animal may have in response to risks of predation. Often evaluations of risk assessment in birds as well as other animals are quantified with metrics such as alert distance (AD) and flight initiation distance (FID), which measure the distance between an animal and an approaching observer when it exhibits alert behaviors and/or when it escapes, respectively.
This study investigated the effects of sound pollution and other factors on the anti-predatory behavior of three bird species in Tainan City, including, Eurasian tree sparrows (Passer montanus), common mynas (Acridotheres tristis), and spotted doves (Streptopelia chinensis). Sampling was conducted in nine different parks/areas within two districts of Tainan City, East District and Anping District, respectively, five in Anping District and four in East District. While both districts have been urbanized, East District exhibits a higher extent of disturbance via its higher human population density and higher mean ambient sound levels when compared to Anping District. The sound level was measured in the geographic center of every park each time at the beginning of sampling. All five locations in Anping District had significantly lower mean levels of sound than all four locations in East District. Percent vegetation cover of each sampling location was also estimated using Google Earth and level of tree coverage present at a location was found to be correlated with most metrics of anti-predatory behavior recorded in all three of the studied species. After sound level was recorded, observations were then conducted on the three aforementioned bird species. Birds were approached at a starting distance of 25 to 30 meters. During each approach, two anti-predatory behaviors, alert distance and flight initiation distance, were measured. Alert distance was defined as the distance between the observer and the bird when the bird began to exhibit alert behaviors, such as stopping foraging and raising the head to where the crown of the head is parallel to the ground. Flight initiation distance was defined as the distance between the observer and the bird when the bird began an escape response. After an escape response occurred, the distance fled (DF) by the bird was also measured. Also, the difference between flight initiation distance and alert distance (buffer distance - BD) was calculated as another way to further quantify risk assessment in the observed birds in this study.
Of the four recorded behavioral assessments (AD, FID, BD, DF) only FID in sparrows was significantly different between sparrows sampled in East District and Anping District. Sparrows in East District had lower FIDs compared to their counterparts within Anping District. While this finding may result from sparrows exhibiting a decreased sensitivity to human activity and thus lowered perceptions of risk from humans in the more urbanized district, variation in the ambient level of sound specifically was not found to be significantly correlated with variation in any of the metrics of anti-predatory behavior. This may possibly be due to variations in sound level during sampling, because of factors such as fluctuations in traffic, not being captured and thus the precise sound level each individual bird was exposed to at the moment of approach was not measured.
Factors that were observed to affect FID, AD, BD, and/or DF significantly were: species, tree coverage, initial substrate, flock size, and time of year. The level of tree coverage at sites was found to be very influential in how birds behaved at each sampling location, with all three species exhibiting lower flight initiation distances, alert distances, and distances fled (DF) in locations with high levels of tree coverage compared to their counterparts in locations with low levels of tree coverage. Furthermore, the strength of association of certain variables (i.e., flock size and season) to variation in flight initiation distance, alert distance, or distance fled were much stronger in sparrows in locations with low levels of tree coverage compared to locations with high levels of tree coverage.
This study identified gradations of disturbance are present even within an already urbanized environment, thus variation of both tolerance to human disturbance and responsive behavior by birds may occur in these locations. In addition, the data of this study indicated that many variables have stronger effects when assessed in more open areas with less tree coverage. Tree coverage likely greatly reduces any perceived risk from birds, especially for smaller birds such as sparrows, and thus reduces the impact of other variables that may possibly affect flight behavior, i.e., season, flock size, sound, etc. Finally, in order to specifically link sound pollution to any changes in responsive behaviors of birds in these areas, the immediate level of sound a bird is exposed to during sampling should be recorded as opposed to the mean ambient level of a given location at a given time.
Keywords: alert distance, antipredator behavior, escape behavior, flight-initiation distance, noise pollution, urbanization

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