Sea birds born ready to kill their siblings
The Nazca booby, a Galápagos Island seabird, emerges from its shell ready to kill its brother or sister. Wake Forest University biologists and their colleagues have linked the murderous behavior to high levels of testosterone and other male hormones found in the hatchlings.
The elevated levels of male hormones, called androgens, increase aggression in both male and female chicks and prepare the birds to fight to the death as soon as they hatch
The older of two Nazca booby hatchlings unconditionally attacks the younger within days of hatching," researchers say. Because Nazca boobies have difficulty raising more than one chick, it is important for the older chick to defeat the younger one in order to increase its own chances of survival.
According to the study, the high hormone levels also cause the surviving chicks to behave like bullies after they grow up. They frequently seek out nestlings in their colony, and during those visits they often bite and push around the defenseless youngsters.
The Nazca booby, a Galápagos Island seabird, emerges from its shell ready to kill its brother or sister. Wake Forest University biologists and their colleagues have linked the murderous behavior to high levels of testosterone and other male hormones found in the hatchlings.
The elevated levels of male hormones, called androgens, increase aggression in both male and female chicks and prepare the birds to fight to the death as soon as they hatch
The older of two Nazca booby hatchlings unconditionally attacks the younger within days of hatching," researchers say. Because Nazca boobies have difficulty raising more than one chick, it is important for the older chick to defeat the younger one in order to increase its own chances of survival.
According to the study, the high hormone levels also cause the surviving chicks to behave like bullies after they grow up. They frequently seek out nestlings in their colony, and during those visits they often bite and push around the defenseless youngsters.
posted by: Hessom Minaei (4)
update
The nazca booby are also found in revillagigedo islands off baja Califonia. These birds lay two eggs, several days apart. If both eggs hatch, the elder chick will push its sibling out of the nest area, leaving it to die of thirst or cold. The parent booby will not intervene and the younger chick will inevitably die. It is believed that two eggs are laid so that one remains an insurance in case the other gets destroyed or eaten, or the chick dies soon after hatching.
Blood samples were taken from the chicks within 24 hours of hatching. In 15 nests with two eggs, blood samples were taken from both hatchlings. Samples were also taken from 15 hatchlings in one-egg nests. Then, blood hormones were analyzed by researchers . For comparison, the researchers did the same for blue-footed boobies, a closely related species.
The researchers suspect that the Nazca booby hatchlings experience the high level of aggression-related hormone during a "sensitive period" in their growth, when long-term growth patterns are easily affected.
Some Nazca booby nestlings experience a one-two hormonal punch, raising their aggression hormones even higher when they actually have a nest mate. The nestlings that fight siblings become bigger bullies as adults than the Nazca booby nestlings who never fight.
Nazca booby chicks have aggression-related hormone levels three times as high as their less aggressive cousins, the blue-footed boobies. Blue-footed boobies do not have the same lethal fights right after hatching and do not go on to bully their fellow birds as adults.
posted by PWH @ 9:09 PM
24 comments
24 Comments:
very interesting article. I was wondering what the populaion of these birds are since many young die..what is the average clutch size? Good Find!
Mia DiFabbio
It makes sense for them to fight and kill their siblings if only one chick can survive for the parent to raise, but I am wondering why they continue to bully chicks when they get older? It doesn't seem that they would be getting any benefit from that.
-Tara Quist
Interesting article. Did the article mention about any other kind of sea birds who has a similar offspring actions, or why they can only usually raise one offspring each time? I wonder if it's just because the resources are not there, or because they invest too much time in each offspring to raise more than one successfully. It's very interesting how all offspring has elevated level of male hormones through out their lives. I would where this evolved?
Katie Cole
This is certainly the opposite of a lot of species - those who protect their families. If they can only raise one chick, why does the species put extra effort into laying more eggs? If the older one wins, it wouldn't be to determine who's genetically superior. Does the older chick ever lose to the younger one? Do the androgen levels vary between chicks ever leading to more than one offspring being raised? Do these birds live by themselves? It would seem if they lived in social groups that they would be in constant conflict with one another.
Allison Cornell (4)
Has there been a case where the older silbing actaully died from trying to defeat the younger one?
- David Huynh
In my marine vertebrates class I learned about sharks who eat their siblings prior to birth and it's interesting to see similar behavior in birds. Are these birds aggressive into adulthood as well?
Amy Kawazoe
If they kill each other after birth that means they have a small population how is it possible that with such a small population that they haven't gone extinct yet? Do they not have any predators? What if one chick wasn't able to kill the other? Will the parent still raise both of them?
Lysander Ning
I am curious as to why it is so difficult for these birds to rear more than one offspring, and also if this is a recently evolved trait or if it has existed in the birds for a long period of time. Does this simply make the chicks more violent meaning they would attack anything nearby (such as the parents) or is the aggression directed solely at the other chicks?
-Alex Jackson
when i first read this article i thought killing your siblings was barbaric. However given the difficulty of finding food i can see why it is important.
-Matthew Sousa
This comment has been removed by the author.
How many eggs are normally laid and hatch per mating season? Is the amount of hormones in the birds inherited fromt he parents or is it environmental, meaning if there is another egg they produce more hormones in order to fight and kill? Do they have a selective food source that restricts adults in caring for their young?
Rob Lubenow
This is interesting because usually animals keep away from killing its own siblings because that would mean lowering the chance of their own genes to be passed on... Why wouldnt theye just kill others of their own species but not their own siblings? I dont really see the advantage of killing your own sibling in a world where genetic transfer is one of the most important things.
-Brena Sena
This is REALLY interesting because of the geographical isolation of the Galapagos. Are the Nazca booby native only to the Galapagos or can they be found elsewhere? If so is this behavior seen in this species away from the islands? This is a perfect example of how early competition for survival can begin. Like Amy Kawazoe said in a post above, there's a reproductive strategy in sharks called adelphophagy, where one shark eats its siblings in utero. I find these strategies fascinating. I wonder how much of the behavior or the selection of the behavior is due to the species location. Why would a bird need to have this strategy similar to sharks? Thank you for your post.
Posted by: Amanda Sceusa
From what we've heard and read I wonder what the cost-benefit is to this behavior? It seems like it would be more beneficial just to lay one egg instead of two to begin with.
Allan Eldridge
This is very interesting...similar to competition between human children haha. Does this affect the entire population? Or do some hatchlings survive and learn to coexist?
Ericka Adey
This is probably a classic example of "survival of the fittest". Do they have limited food resource to cause them to behave this way? Because it is somewhat unusual that the parents cannot raise more than one chick. Have they always tried to kill their siblings or did this behavior evolve over time?
Hanbing Guo
I wonder how a chick without any brothers or sisters behave as a chick and an adult.
Charles Scondras
Lately it seems I've been reading a lot about hormone levels linked to behaviors in birds, especially the testosterone and aggression factor. Birds have very different behavioral patterns between species, but it seems each different type of bird is affected by testosterone levels, especially at an early age. It is how the birds react to the different levels that makes them unique in their species. Why is it do you think that birds that do not need to kill the other babies still display levels of agression at youth?
-Alicia Stein
Just like we studied in class about the indoor mouse father killing other baby mouse. I am really surprise to hear that there are other animals that does just as scary think as the indoor mouse. Killing one’s own sibling seems too extreme for me but thinking back to what we have learned in class it seems natural. I meaning when in class we learned about the feeding method in baby bird, about how only the big mouth with long neck get fed, another form of killing its own siblings in a non-direct way. I am talking about the ones that have shorter neck or smaller mouths that don’t get any food.
-Tenzing Y. Dundutsang
Do you know exactly why the parents can't raise more than one offspring? Are there cases where the young are actually able to survive and the elder one dies instead? Interesting article!
Tazneena Ishaque
This is very odd behavior and I would never think birds act like this. Are there other species that behave this way? It seems to go against human natural instincts. It also seems odd to me to kill relatives. Compared to the salamander situation we learned about in class, how the carnivorous ones don't eat their relatives because they would be diminishing genes similar to their own. Its very interesting to think in nature for this species it must have some beneficial aspect or else this species would be extinct by now.
-Julie Riley
Will only one baby bird survive?
yes, most of the time the older chick is the only chick that survives, the parent booby will not pay much attention to the younger chick if it is kicked out of the nest or beaten by the older chick since it is realy hard for the parent booby to raise two chicks.
-Hessom Minaei
Okay, if this were true, there would be no females left.
If there are females left, then it is not "male" hormones doing this, but hormones that are found in both sexes.
Post a Comment
<< Home