鸟类体型变大 是气候变迁还是全球变暖所致

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.”

据英国《每日邮报》11月8日报道，科学家们指出，鸟类体型增大以抵抗恶劣的风雪天气与气候变迁有关系。

一项贯穿40年的研究发现，加利福尼亚州中部的鸟类与25—40年前相比，体型明显增大。

例如知更鸟，自从20世纪80年代以来翅膀增长了八分之一英尺，体重增加了0.2盎司。

平均而言，加利福尼亚州中部的鸟类体重和翼展都增加了2%—5%不等。

研究人员指出鸟类体重的增长能帮助其在全球气温上升的大环境下度过越来越不稳定的气候状况。

该研究结果发表在了《全球变化生物学》上，与先前的研究意见相左。

一项生态法则——博格曼氏法则——说生活在高纬度地区的鸟类和哺乳类动物体型会有增大的趋势，这种改变或许是为了保持体温。

按照该理论，鸟类和哺乳类动物为了适应全球气温上升，体型应该变小。

以旧金山州立大学的研究生瑞伊-古德曼为首的研究人员写到：“先前来自世界其他地域的研究证明了鸟类的体型是缩小的，可以用伯格曼氏法则和全球气候变暖来解释这些变化。”

“因为我们的研究结果不支持这一模式，所以我们提出生活在加利福尼亚洲中部的鸟类，它们体型变化不是全球变暖所致，而是受到了气候变迁的影响。”