Would you raise the bird that murdered your children? - Steve Rothstein

譯者: 柏陞 郭 審譯者: Helen Chang

This is a little bee-eater’s nest.

這裡是蜂虎的小巢穴，

But this is not a little bee-eater chick.

但這隻卻不是蜂虎的雛鳥。

It’s a newly hatched honeyguide— and it’s much more lethal.

這剛孵化的嚮蜜鴷 並不怎麼和藹可親。

When its mother placed it here, she punctured all the other eggs in the nest.

當母嚮蜜鴷把蛋放在這時， 牠把巢內其他所有的蛋都戳破了。

However, one little bee-eater chick survived the attack and is now hatching.

但這時有一隻小蜂虎躲過攻擊， 而且正要破殼而出。

Although the honeyguide nestling is still completely blind,

雖然小嚮蜜鴷此時 幾乎看不見。

it instinctively stabs the little bee-eater chick

牠卻能憑直覺地用尖鉤狀的喙

with its sharp, hooked beak.

把小蜂虎捅死。

And over the following weeks,

在幾個星期後，

the host parents devotedly care for the hatchling

這個謀殺孩子的兇手 甚至得到受害者雙親

that murdered their offspring.

無微不至的照顧。

This is but one example of brood parasitism,

這是巢寄生的一個例子：

an evolutionary strategy in which one animal tricks another

藉由欺騙另一種動物 養育自己後代的演化策略。

into rearing its young.

It’s especially well-known among birds.

這類情形在鳥類中猶為常見。

By depositing their eggs into a stranger’s nest,

寄生者把自己的蛋下在 另一種鳥的巢裡，

brood parasites are able to shift the major costs of parenting onto others.

藉此將養育後代的責任轉嫁牠者。

Brood parasite chicks usually hatch early,

寄生者的雛鳥通常較早孵化，

then monopolize their host parents’ attention.

因此獨佔宿主雙親的目光。

Some stab their fellow nestlings to death,

有些寄生者會把其他手足捅死，

while others shove the remaining occupants out of the nest.

另一些則是將餘下的手足擠出巢外。

Meanwhile, others are less harmful to their hosts.

除此之外，也有對宿主造成 較少危害的品種。

Not all brood parasites kill all of their host’s offspring outright.

並不是所有的巢寄生者都會 徹底殺害宿主的後代。

Brown-headed Cowbirds usually outcompete them

像是褐頭牛鸝的幼鳥 就是透過優勢競爭取勝。

by begging for food louder, more frequently, and with a wider mouth.

他們憑著更宏亮、頻繁的叫聲 還有大嘴討到食物。

Among the most benign,

而說到最仁慈的寄生者，

black-headed ducks lay their eggs in other nests to be incubated.

黑頭鴨則是把牠們的蛋下在 別人巢內代為孵化。

However, a few hours after hatching, they simply saunter off.

在幾個小時過後， 孵化的幼鳥便自行離開。

But in the most egregious cases of brood parasitism,

但在最嚇人的巢寄生案例中，

why don’t host parents take a stand?

為何不見宿主雙親抗議呢？

In fact, hosts will often drive adult brood parasites away from their nests,

事實上有的，宿主通常會把 成年的寄生者趕走，

and many take their defenses further.

有部分宿主甚至會加以防範。

But whether a hosts can recognize and reject parasitic eggs and nestlings

但是宿主是否能夠識別和拒絕 寄生的卵和雛鳥

seems to depend on a few factors.

似乎取決於幾個因素。

Eastern phoebes will accept

像是東菲比霸鶲就接受 褐頭牛鸝的斑點蛋出現在他們巢裡，

a Brown-headed Cowbird’s speckled egg into their nest,

though theirs are pure white.

儘管牠們自己的蛋是全白的。

The gray catbird, on the other hand,

至於灰貓嘲鶇則是位 精於檢驗相仿寄生蛋的專家。

is an expert at rooting out the very same parasites.

It memorizes what the first egg in its nest looks like,

牠記得自己第一顆 在巢裡的蛋長什麼樣子，

which is usually its own, and tosses any aberrations.

因此牠會辨認並把 不屬於自己的蛋扔掉。

This retaliatory adaptation can fuel an evolutionary arms race

宿主的反擊措施促使了 一場演化競賽，

where brood parasites evolve eggs that closely mimic their host’s.

讓巢寄生者的蛋慢慢演化成 與宿主的外型近似。

Interestingly, birds that do reject parasitic eggs

有趣的是，那些不接受寄生蛋的鳥

are usually clueless when it comes to parasitic chicks.

在面對孵化的寄生幼鳥時 經常顯得毫無頭緒。

Reed warblers are good at ejecting poorly matching cuckoo eggs.

蘆葦鶯就善於排除 迥異的杜鵑鳥蛋。

But if one hatches in their nest,

但若是對方先在巢裡孵化了，

they’ll care for it even after it’s grown six times their size.

牠們仍會照顧好杜鵑鳥， 就算後來長到牠們的六倍大。

Though chick rejection is a rarer phenomenon,

雖然拒絕養育幼鳥是個 不常見的現象，

there are some noteworthy examples.

但還是有幾個例子 值得我們注意。

While incubating its eggs, the Australian superb fairy-wren sings to them,

在養育雛鳥時，壯麗細尾鷯鶯 會唱歌給牠們聽。

imparting a unique note that its chicks use as a kind of password.

而雛鳥會把這首獨特的旋律 學起來做為密碼。

When a cuckoo is in the wren’s nest, it hatches first and pushes the others out.

細尾鷯鶯巢裡的杜鵑鳥會先孵化， 還把其他的雛鳥推出鳥巢。

But, perhaps because it hatched sooner,

但是，也可能因為牠孵化得早，

the cuckoo chick wasn't able to learn the password,

杜鵑鳥沒辦法學到這組密碼。

and so it doesn’t croon the right begging call.

因此牠就不會哼出對的乞求旋律。

At this point, the adults usually abandon their nest and start another.

這時候，成鳥經常就放棄 這個巢轉而另尋他處。

Altogether, host species show a remarkable variety of responses.

總而言之，作為宿主的鳥類展現 各種不同的應對方式。

This seems to partially be a result of how long

這就部份說明巢寄生已存在於 他們生長環境中

brood parasitism has been in their environment,

有一段很長的時間了，

and thus how much time they've had to evolve suitable adaptations.

因此牠們也必須花時間 發展出各種應對方式。

In fact, studies have shown that those hosts that reject parasitic eggs

事實上，有研究指出那些 不接受寄生蛋的鳥

less frequently can visually distinguish between their eggs and a brood parasite’s.

很少透過視覺去分辨 自己和寄生者的蛋。

They simply lack a response to the visual information.

牠們鮮少對可見情報有所反應。

This is probably because, before brood parasitism appeared,

原因大概是因為在巢寄生出現前，

responding would have likely had no adaptive value.

這種洞察力根本沒有實用價值。

And even when hosts do recognise a parasite,

即便宿主能夠辨認寄生蛋，

getting rid of it may not be the best option.

排除牠們也未必是最好的選擇。

The host, especially if it’s small, might not be able to kill the parasite—

尤其是身形嬌小的鳥類， 牠們大概也沒有能力破壞寄生蛋，

or could risk breaking its own eggs in the process.

還可能冒著過程中誤殺自己蛋的風險。

Unless the brood parasite kills all of the host’s young,

除非寄生者殺害 宿主全部的幼鳥，

it may be best to simply foster the imposter.

最折衷的方法還是養育這名冒充者。

Brood parasitism tends to evoke horror and disdain.

巢寄生往往引起人們恐慌和鄙視。

But why should it be thought of as any more objectionable

但何必把它視為比獵食者 和獵物還要可憎的關係呢？

than predator-prey relationships?

And is it ever productive to impose human morals onto other animals?

強加人類的道德觀在動物上 有什麼成效嗎？

Or does it end up saying more about us than it does them?

或者我們應該停止 以這種想法談論動物們？

Whichever way you swing it,

無論你的想法是哪一個，

brood parasitism is yet another example of the fascinating turns evolution has taken.

巢寄生依舊是演化過程中採取的 一個富有趣味的策略。