鳥類體型變大 是氣候變遷還是全球變暖所致

Birds are getting bigger to survive harsh storms related to climate change, scientists have suggested.

A study spanning 40 years found that birds in central California are significantly larger than they were 25 to 40 years ago.

Robins, for example, have increased by an eighth of an inch in wing length and about 0.2 ounces in weight since the 1980s.

On average, birds in central California have bulked up between two and five per cent in body weight and wingspan.

Researchers suggested this increase in body weight is to protect the birds during increasingly erratic weather as global temperatures rise.

The findings, published in Global Change Biology, are at odds with previous research.

One ecological benchmark, Bergmann’s rule, states that birds and mammals tend to be larger at higher latitudes, perhaps to conserve body heat.

In keeping with this reasoning, birds and mammals would get smaller to adapt to rising global temperatures.

The researchers, led by San Francisco State University graduate student Rae Goodman, wrote: “Previous studies from other regions of the world have documented decreases in avian body size and have used Bergmann's rule and increases in mean temperature to explain these shifts."

“Because our results do not support this pattern, we propose that rather than responding to increasing mean temperatures, avian body size in central California may be influenced by changing climatic variability.”據英國《每日郵報》11月8日報道，科學家們指出，鳥類體型增大以抵抗惡劣的風雪天氣與氣候變遷有關係。

一項貫穿40年的研究發現，加利福尼亞州中部的鳥類與25—40年前相比，體型明顯增大。

例如知更鳥，自從20世紀80年代以來翅膀增長了八分之一英尺，體重增加了0.2盎司。

平均而言，加利福尼亞州中部的鳥類體重和翼展都增加了2%—5%不等。

研究人員指出鳥類體重的增長能幫助其在全球氣溫上升的大環境下度過越來越不穩定的氣候狀況。

該研究結果發表在了《全球變化生物學》上，與先前的研究意見相左。

一項生態法則——博格曼氏法則——說生活在高緯度地區的鳥類和哺乳類動物體型會有增大的趨勢，這種改變或許是爲了保持體溫。

按照該理論，鳥類和哺乳類動物爲了適應全球氣溫上升，體型應該變小。

以舊金山州立大學的研究生瑞伊-古德曼爲首的研究人員寫到：“先前來自世界其他地域的研究證明了鳥類的體型是縮小的，可以用伯格曼氏法則和全球氣候變暖來解釋這些變化。”

“因爲我們的研究結果不支持這一模式，所以我們提出生活在加利福尼亞洲中部的鳥類，它們體型變化不是全球變暖所致，而是受到了氣候變遷的影響。”