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Friday, August 07, 2020

Sibling rivalry in animal kingdom

Unlike human greed, it's usually the lack of food that makes sibling rivalries among avians and mammals to frequently take a deadly turn, leading to siblicide

Written by Ranjit Lal | Published: August 2, 2020 6:35:17 am
egrets No love lost: Siblicide happens frequently among egrets (Source: Michaell Baird/Wikimedia Commons)

It’s probably one of the most distressing things a nature lover could witness. We tend to get all mushy when we see fluffy new chicks in a nest, frantically begging for food and their parents’ unconditional love and affection. But what goes on in many bird homes is diabolical – the murder of the smallest, youngest member of the family, by its elder brother or sister, often when the parents are away. Not that the parents cover themselves in glory when this happens: they just ignore the battered little one, and carry on spoiling the elder lout with choice tidbits. No chastising, or saying things like, “Baby, aisa nahin karte hain, sorry bolo (Baby, you are not to do things like this. Say sorry!)” In fact, the parents are primarily responsible for matters to reach such a pass. Many birds, for instance, deliberately lay their eggs at intervals. Obviously, the first chick to hatch gets all the attention – and most of the food. The second egg, hatching after a while, is merely an insurance policy in case something dreadful happens to the older laadla or laadli.

I first witnessed this happening in a black kite’s home in Mumbai, years ago. The elder lout went hammer and tongs at its younger sibling, who could only squeak plaintively – not that it had any effect on its mom. She just stuffed the face of the lout and ignored her baby. Of course, it ultimately died. This is a frequent happening in the homes of raptors where the parents raise just a single chick and the second is dispensable after a while. You can also see this happening in colonies of water birds such as egrets and herons – and here the weapon used by the elder chick is its own spear-like bill. If the nest has been built over water, another sinister element comes into play. Even if a chick is thrown out of its nest, it can often, somehow make it to the lower branches of a tree or a fallen log. But not when there are crocs or predatory fish circling in the water, waiting for just such an opportunity. The chick’s last moments are not pretty.

So why do siblings display such love and affection towards each other? It usually happens when food sources are scarce, resulting in intense competition between siblings. The raptors just cannot pick up enough prey, or the herons and egrets enough fish to feed their brood. So, sacrifices have to be made – and the eldest chick is happy enough to oblige. But there’s a ruthlessness to the way the chick goes about its task that makes you look at these birds with mixed feelings: you watch a white egret float gracefully across the sky and you wonder, “It’s probably a chick murderer!” Can there be anything worse?

Yes, there can. I guess even hard-boiled, unsentimental researchers must have been horrified when they discovered what the sand tiger-shark baby did to its potential brothers and sisters. They found that in the mom’s womb, the embryo that develops fastest, first digests its own yolk and then cannibalises its brothers and sisters – regardless of whether they were in egg form or embryos.

Higher up on the evolutionary scale, siblicide happens among mammals, too. When sows have huge litters and there’s not enough milk at mama’s milk bar, vicious fights break out amongst the piglets. The runts, of course, get shunted. The same thing happens with spotted hyenas, where a pecking order has to be established early. But, often, it can be worth having siblings: that’s primarily how cubs learn: how to stalk, pounce and hunt. Also they have the same energy levels – which their parents may not. Trouble amongst these siblings usually begins later in life, when they are adults, each vying for independent territory. Again, some animals have been able to avoid conflict: lion and cheetah brothers band together in coalitions and their sisters stick together with each other, too. For the boys, it makes hunting and hostile pride takeovers easier; for the girls, bringing up cubs and protecting them from hostile pride takeovers (during which the cubs are invariably killed by invading males). Even such proudly independent species as tigers have been documented getting together to form coalitions, within the family.

Thankfully, not all bird parents behave reprehensibly. Some take pains to make sure that all in the brood are fed equitably. Of course, this becomes so much easier when food is plentiful. But I’ve yet to see the family bully being given a spanking or made to stand in the corner by its parents for hustling its younger brother or sister!

Even “lowly” creatures like spiders go in for this sort of thing. If food is scarce, spiderlings will turn on each other for sustenance, and, alas, sometimes even their mom helps herself to some of her babies.

And then, of course, there’s us – human beings. We’re really not very different, are we, judging by the number of families that have been ripped apart by sibling rivalry? There’s one distressing difference though: among animals it’s the lack of food that causes all the bitterness, while with us – especially the filthy rich – it’s just naked greed for the biggest slice of the pie.

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