Why are beavers obsessed with dams? - Glynnis Hood

譯者: Camila Lin 審譯者: Helen Chang

Nestled in the remote forests of northern Canada

北加拿大的偏遠森林中，

sits the world’s longest beaver dam.

有著世界上最長的河狸水壩座落其中。

Curving around the water like a castle wall,

水壩像城牆般在河中蜿蜒，

this 850-meter-long structure is large enough to be seen in satellite imagery.

全長達 850 公尺， 大到可被衛星影像清楚拍下。

The dam and the generations of North American beavers that maintain it

這座水壩與負責維護它的 北美河狸家族，

have dramatically transformed the region,

已為這個區域帶來巨大轉變，

creating a pond containing roughly 70,000,000 liters of water.

即打造出一個約七千萬公升的湖。

This is a suitably sizable home for the creators of this woodland kingdom.

對打造出這個木頭王國的河狸們來說， 這座湖是尺寸合宜的安樂窩。

But even dams 1/100th the size of this one

但就算尺寸只有這個水壩的百分之一，

can have huge impacts on their environment.

河狸水壩也能大幅改變環境。

So how exactly do beavers redesign the forest,

那麼，河狸到底是怎麼改造森林，

and how do they build these impressive structures in the first place?

又是怎麼蓋出這麼厲害的水壩的呢？

Consider this beaver in the northwestern US.

看看這隻住在美國西北部的河狸。

Standing just under 2 feet tall,

雖然牠的身高大概只有 60 公分， 卻是世界上第二大的齧齒動物的一員。

he’s a proud representative of the world’s second largest rodent species.

While he’s at risk to predators on land, once he’s built a lodge,

雖然在陸地上會受到掠食者威脅， 但只要牠做個巢穴，

he’ll have a massive moat to keep him safe.

牠就有條巨大的護城河， 隔絕一切危險了。

But he can’t just build a dam anywhere.

但牠可不能想在哪蓋水壩就蓋。

Following the sounds of running water,

我們的這隻河狸，

our beaver searches heavily wooded areas

循著水聲，在茂密的樹林中找尋

to find a medium-sized stream that’s not too steep or too deep.

一條沒有陡坡、深度適中的中型河流。

After abandoning one construction site due to its rocky floor,

在牠因為岩石河床而放棄一個建地後，

he finds a stream with a soft, muddy bottom.

牠終於找到一條擁有柔軟泥地的河。

Combining vegetation, mud, and sticks,

把植物、泥土和樹枝混在一起後，

he creates a small bank along the stream’s edge.

牠用這些材料， 沿著河沿做出一個小堤岸。

Then, using a bite almost 3 times stronger than any other mammal of this size,

河狸的咬合力， 約比同體型的哺乳類強三倍。

our beaver chews nearby logs into sturdy sticks.

藉著咀嚼，牠把附近的木頭 雕成結實的木棍，

He then rolls them into the water and spikes them down into the soft streambed.

再將木棍滾到河裡，插進泥土河床。

Beaver dams come in several shapes,

河狸的水壩有很多種形狀，

but our beaver opts for a concave dam to dissipate the forceful flowing water,

不過這隻河狸決定蓋個凹型水壩，

這樣就能分散強勁的水流，

and layers in large rocks to reinforce areas

並用疊起來的大石頭， 加固水流最強的地方。

where water flows the strongest.

Depending on a dam’s length, the stream’s speed,

視水壩長度、水流速度

and the number of beavers on the job,

與河狸建築工的數量而定，

these devoted architects can build shockingly fast.

這些敬業的工程師， 有時候能用超快的速度完工。

In some cases where humans tried to remove dams,

在某些案例中，人類試著拆除水壩，

beavers have rebuilt them overnight—

河狸們卻在一夜之間就蓋了個新的，

sometimes rebuilding larger than they were before.

有時候甚至蓋得比原來的水壩更大。

Like most dams, our beaver’s project

這隻河狸的水壩， 和大部分的水壩差不多大，

is just a couple meters long.

只有幾公尺長。

And working alone, this dam could take several days to complete.

因為沒有其他河狸幫忙， 牠需要好幾天才能完工。

But once the structure spans the channel, his watery home begins to fill up.

但只要水壩延伸成水道， 牠在水中的巢就會開始注水。

As the pond grows,

在湖逐漸變大時，

he’ll extend the dam to block water flowing around the sides.

牠會擴建水壩，不讓水從兩旁溢出。

However, some is permitted to leak downstream,

不過，牠也會讓一些水流到下游，

releasing pressure on the dam and regulating the pond’s water levels.

以釋放水壩承受的壓力， 並調整湖的水量。

The larger the pond, the larger the beaver’s territory.

湖越大，河狸的地盤也就越大。

And since they can hold their breath for up to 15 minutes,

而因為河狸可以 閉氣長達 15 分鐘，

beavers can easily access food along the shorelines.

牠們便能輕鬆沿著水壩覓食。

Throughout the fall, our beaver builds up an impressive supply for winter—

這隻河狸把整個秋天，都花在 打造一個為過冬準備的豐富糧倉，

while also looking for someone to share it with.

以及尋找共享食物的另一半上。

Beavers are fiercely territorial, but they also bond for life.

河狸的領地意識非常強， 但牠們也遵行一夫一妻制。

When the pond freezes over,

在湖面結冰的時候，

our new beaver couple splits their time

這對新婚河狸夫婦，

把時間花在從巢穴通道去食物儲藏室，

between making trips to the food cache with their lodge’s private entrance

and starting a family.

以及養育後代上頭。

Come summertime, the juveniles will help reinforce and expand their dam,

夏天到來時，孩子們 會幫忙修理、擴充水壩、

gather food, and watch their younger siblings.

收集食物，並照顧弟弟妹妹。

After 2 to 3 years,

2 、 3 年後，

these young beavers will disperse to find territory and mates of their own.

這些年輕的河狸便會離家， 找到自己的地盤和伴侶。

But their ancestral dam can last for decades.

但這座祖傳的水壩可以屹立數十年。

Maintenance work is continued by descendants of the original colony,

維護水壩的工作， 會由留在老家的後代負責，

or new beavers that move in when the reigning family leaves.

或是那些在原居民搬走後 遷入的外來河狸負責。

There’s certainly no shortage of neighbors—

河狸從來不缺鄰居：

some regions have as many as 40 beaver dams per kilometer of stream.

在某些地方，每公里的河流 就有 40 座水壩。

This is great news for surrounding wildlife

對附近非常依賴這些半水生建築師的 野生動物們來說，

that rely heavily on these semi-aquatic engineers.

這是個再好不過的消息。

Lodges can serve as nesting sites and refuges for various species of waterfowl.

許多水鳥把河狸的巢 當作繁殖地或避難所。

Beaver channels also connect bodies of water,

河狸的水道也能連結水體，

increasing the biodiverse areas between water and land.

提高濕地的生態多樣性。

Humans benefit from beaver construction projects too.

人類也能從河狸的水壩中獲益。

Their ponds help replenish groundwater stores,

河狸打造的水庫，創造出大片地面水，

in part by creating large expanses of surface water.

這有助於補充地下水。

And just like their manmade counterparts,

而就像我們蓋的水壩一樣，

beaver dams slow floodwaters.

河狸的水壩也能減緩洪水。

So just by following their natural instincts,

所以，河狸們只是順從本能，

these ecosystem engineers create huge impacts downstream.

就成了生態系統建築師， 為下流帶來巨大改變。