Easy Parenting: Brood Parasites Get Someone Else to Do the Hard Work

Friday, September 25th, 2020 | Petrina Duncan | No Comments

 For most birds, reproduction is a life process that takes up a lot of time and energy. There are huge energetic costs to a female bird with respect to mating, egg-laying, incubating the eggs and feeding hungry chicks for many weeks or months. Some birds also migrate vast distances across land and sea before breeding can commence, using up even more time and energy. Breeding for a bird is a lot of hard work.

So, if a bird found an easier way to become a successful breeder, we would expect that behaviour to be favoured by natural selection and become fixed. In about 1% of all bird species, that’s exactly what has happened: it’s called brood parasitism.

Brood parasites are birds who have learned how to make the parenting process much easier. They still have to find a partner and mate successfully, but instead of the female bird laying her eggs in a nest that she and/or her partner made, she stealthily lays them in the nest of another bird. Intraspecific brood parasites lay eggs in nests belonging to birds of their own species, compared to interspecific brood parasites who target other bird species.

Common cuckoo chick in the nest of a tree pipit.

Common cuckoo chick in the nest of a tree pipit.

 

 

 

 

 

 

 

Benefits and advantages for the brood parasites:

  • Increased breeding output
  • Minimal energy expenditure because they don’t defend a nest, incubate eggs or feed chicks.
  • Genes passed on to the next generation.

Costs and disadvantages for the host birds:

  • Decreased breeding output
  • Expending more energy raising someone else’s offspring, especially if the parasitic chick is very large as more food will have to be found.
  • Not passing on genes to the next generation.

Generalists and Specialists

Some brood parasites put their eggs into the nests of a wide variety of other species. These are called generalists. An advantage of this behaviour is the flexibility it offers. Generalists can be successful in many different places and at almost any time, as long as a suitable host bird is nesting nearby.

Alternatively, brood parasites can be specialists. They will target one species to be the host of their egg/s. The limiting factor in this approach is the lack of flexibility, as parasites must live close to their host species or spend time and energy travelling to find them during the breeding season.

 Brood parasites in New Zealand

Cuckoos are the most famous brood parasitic birds worldwide. In New Zealand, two migratory species of cuckoos arrive on our shores in September and October each year. The shining cuckoo/pīpīwharauroa (Maori name) is the smaller of the two species. These small birds fly all the way from the Solomon Islands and the Bismarck Archipelago, a distance of more than 5000 kilometres. On arrival in NZ, shining cuckoos/pīpīwharauroa seek out their target host species, the tiny grey warbler/riroriro, in forests and gardens across the whole country.

Shining cuckoo/pīpīwharauroa being fed by its host parent, a grey warbler/riroriro.

Shining cuckoo/pīpīwharauroa being fed by its host parent, a grey warbler/riroriro.

 

 

 

 

 

 

 

 

 

Long-tailed cuckoos/koekoeā fly to NZ from even further away. They spend winter in an arc of Pacific Islands which extends from Henderson Island (Pitcairn group) in the east to Palau in the far west of Micronesia. A long-tailed cuckoo/koekoeā migrating from Palau to NZ will fly more than 6700 kilometres – perhaps that’s why they don’t have the energy to be a ‘normal’ bird parent. They arrive in NZ in September and October to begin searching for their target host species. In the North Island, they look for a small bird called the whitehead/pōpokatea in tall, mature forests. The forests of the South Island have two host species for long-tailed cuckoos/koekoeā: the brown creeper/pīpipi and the rarer yellowhead/mohua. All three of these host species are endemic to NZ and closely related.

Whitehead host parent feeding a young long-tailed cuckoo

Whitehead host parent feeding a young long-tailed cuckoo

 

 

 

 

 

 

 

 

 

 

 

Strategies of a successful brood parasite

  • Be selective. Brood parasites take their time to find the best host ‘mum’ to be a surrogate parent for their offspring. In human terms, this is a like parents shopping around to find the very best day care centre for their toddler. Before putting her eggs into a host’s nest, the parasitic bird will watch a potential ‘mum’ closely to appraise her age, condition, singing ability, territory location, size of the nest and its location. These factors will contribute to the parasite’s final choice of the best host for the job.
  • Team Work. Some parasitic bird pairs work together to achieve their goal. For example, male great spotted cuckoos in Southern Europe will stage an attack on an unsuspecting pair of magpies. The male cuckoo appears in full view of the magpies to divert their attention and launch a pretend attack. Meanwhile the female cuckoo sneaks into the magpies’ nest to quickly lay her egg. This risky egg-laying behaviour is only possible because both the male and female are working as a team to ensure the hosts don’t see what’s happening.
  • Egg mimicry and timing of laying. Parasitic bird eggs have evolved over time to look and feel very similar to the host’s eggs, a concept called egg mimicry. This reduces the chance of egg rejection by the host. Their eggs also usually have thicker shells than the host’s eggs. Parasitic birds will also strategically time their egg laying. By waiting until the host has already laid a few eggs, the parasitic female ensures that incubation is already underway.
The larger blue egg is that of the parasitic common cuckoo. The cuckoo’s egg looks very similar to those of the host, a common redstart

The larger blue egg is that of the parasitic common cuckoo. The cuckoo’s egg looks very similar to those of the host, a common redstart

 

 

 

 

 

 

 

 

 

  • Chicks who are bullies. Brood parasite eggs generally hatch earlier than the host’s eggs. The parasitic chicks use strategies like pushing the host’s eggs and chicks out of the nest or stabbing chicks with a special hook on their beak. Imposter chicks also tend to make louder, more frequent begging sounds to ensure they get all the food from host parents. Some species like NZ’s shining cuckoo have chicks who can mimic the begging call of a grey warbler’s chicks, ensuring the host is fooled into feeding them.
  • Total destruction of eggs. Sometimes a cuckoo misses the chance to lay her eggs at the optimum time. As an extreme measure, she will destroy the entire egg collection in the host’s nest. This behaviour is like a reset for the host bird to start over with breeding. She will probably mate again and lay another clutch of eggs while the watchful parasite bird prepares to intercept at just the right time.
Common cuckoo chick in host nest

Common cuckoo chick in host nest

 

 

 

 

 

 

 

 

 

 

Can host birds fight back?

Brood parasitism is a classic coevolutionary “arms race”. Each time a host species evolves a new behaviour to defend against brood parasitism, the parasite species evolves a new trait which makes its breeding strategy more successful. Here are a few ways in which hosts can fight back.

  • Egg recognition. Many host birds have evolved to be experts at egg recognition. They will recognise and then reject eggs which look different to their own. Sometimes a host will even leave its nest entirely if a strange looking egg appears. However, brood parasites have adapted to this selection pressure by either becoming generalists (they parasitise multiple species) or producing eggs which are almost identical to the host’s eggs (egg mimicry).
  • Chick recognition. Some host ‘mums’ are able to recognise and reject chicks which are not their own. However, rejecting chicks carries the risk of mistakenly rejecting their own chicks. If the rate of parasitism is very high, selection for accurate chick recognition will be stronger.
  • Nest features. Species that commonly get parasitised may deploy nesting tactics to minimise interference. Their nest may be well camouflaged to avoid detection. The nest’s location could be away from places where parasitic birds can sit. The nest entrance may be too small for the brood parasite to enter. For example, the grey warbler’s nest entrance is tiny, preventing shining cuckoos from entering. But the cuckoo manages to parasitise their nests regardless. Researchers suspect the egg is laid elsewhere then carried in the cuckoo’s beak up to the warbler’s nest and carefully deposited inside.

Should we be concerned about brood parasitism?

As our climate changes and the human population continues to increase, natural habitats such as forests are disappearing due to fires, logging, agriculture and urban sprawl. For bird species that are already in decline due to habitat loss, brood parasitism  may pose a significant threat, especially if generalist parasites increase in numbers. Reproductive success will be compromised at a time when the population is already decreasing. The combined pressures could become too much, putting the species at risk of localised extinction.

On the bright side, a brood parasitic species can’t survive without its host species. Parasitic birds often wait until their target host has raised one clutch of offspring before parasitising the second nest. This is a behaviour which will give rare host species a helping hand.

Grey warblers will often raise a family of chicks successfully early in spring, before the shining cuckoos arrive in NZ from their long migratory journey. Even if the grey warbler’s second nest gets targeted by a shining cuckoo, they have already contributed their genes to the next generation and hopefully the behaviour of early nesting was also passed on to their offspring.

For rarer NZ bird species such as the yellowhead/mohua and whitehead/pōpokatea, being less successful breeders due to parasitism by long-tailed cuckoos/koekoeā is a concern to conservationists. Long-tailed cuckoos are also able to parasitise the nests of the more common brown creeper/pīpipi in the South Island. As yellowhead numbers decrease, brown creeper numbers may also begin to decline due to being parasitised at a higher rate. In the North Island, whiteheads are increasing in numbers due to human conservation efforts which will hopefully help to mitigate the negative effects of brood parasitism.

Conclusion

Brood parasitism represents a rare and unusual parenting strategy. There are many benefits for the bird who does the parasitising such as avoiding most of the hard work involved with being a parent.

Brood parasitism is a great example of coevolution in which the evolutionary “arms race” is played out in the privacy of a nest or within the boundaries of a territory. There will always be winners and losers in this host-parasite exploitative relationship. What we must try to do is reduce or eliminate human-related pressures which adversely affect the breeding success of birds. By helping to conserve native bird species and their habitats, we’ll be supporting them to withstand the negative impact of brood parasitism long term.

Further reading:

Photo Credits:

Common cuckoo chick in the nest of a tree pipit.
Vladlen666/WikiMedia Commons (CC1.0)
https://www.sciencenews.org/blog/wild-things/cuckoos-may-have-long-lasting-impact-other-birds

Shining cuckoo/pīpīwharauroa being fed by its host parent, a grey warbler/riroriro.
Photography by Robin Colquhoun. From NZ Birds Online: http://www.nzbirdsonline.org.nz/species/shining-cuckoo#bird-photos

Whitehead host parent feeding a young long-tailed cuckoo. Photography by Adam Clarke.
From NZ Birds Online: http://nzbirdsonline.org.nz/species/long-tailed-cuckoo

The larger blue egg is that of the parasitic common cuckoo. The cuckoo’s egg looks very similar to those of the host, a common redstart. Photography: Dr. Tomas Grim. https://phys.org/news/2018-05-russian-cuckoo-invasion-alaskan-birds.html

Common cuckoo chick in host nest. Photography by Per Harald Olsen (CC BY 2.0)
https://www.birdorable.com/blog/bird-term-brood-parasite/

Are ALL Viruses Bad?

Thursday, March 26th, 2020 | STEPHEN BRONI | No Comments

graphic of sausage-shaped bacteria with pin-like viruses attachedWith all that is going on  around us,  all across this beautiful planet of ours and the word `virus’ dominating everything we see, hear, read in the media at the moment I found myself thinking “Are all viruses bad? Are there any useful, beneficial viruses? And  why  ARE bats  such good carriers  off so many nasty diseases – over 60 of them!”

It seems highly likely that viruses do play a substantial part in maintaining a healthy body.  You have probably heard of our `microbiome’ but what about our ‘virome’
Read more here:
How ‘good’ viruses may influence health 
Here:
Not All Viruses Are Bad For You. Here Are Some That Can Have a Protective Effect
And here:
Viruses Don’t Deserve Their Bad Rap: They’re The Unsung Heroes You Never See
[In  the embedded Ted-X talk in this link, the always engaging, Peter Pollard also  illustrates some illuminating facts about how much C02 freshwater ecosystems pump into the atmosphere, due in part to viruses… everything is linked! ]

And on the question of why bats are such good carriers of disease.Brown bat in flight
Check out:
Why Do Bats Transmit So Many Diseases?

BEFORE YOU CLICK-  Spend a minute thinking about what you know of bat behaviour and basic physiology …. (The answer may take flight in your head…(hint))

 

However, when all is said and done our thoughts are all on one virus at the moment.

Ever wondered how the tests for Coronavirus work?
May you never have to take one!

P.S.
Need a refresher on just exactly what viruses are and how they work?
Check out this great Khan Academy Tutorial on Viruses and the  text Q&A that follows.

Stay safe
Be patient

Futuristic Animals from the Past?

Wednesday, August 15th, 2018 | STEPHEN BRONI | No Comments

Futuristic animals from the past? 

Harriett Spoelstra – Ruawai College

 

The enclosure is empty; the dinosaur has disappeared! Scientists are unable to control this creature, this monster – deadly but amazing. We’ve all yelled at the screen as movie characters act dramatically stupid; at the scientists in Jurassic World who create a creature too powerful to control or understand; at the cartoons with the evil scientists who accidentally make a supervillain. This hunger to learn everything, to create something just because you can is what makes these characters so memorable.
Scientists (a term that covers a whole range of people and jobs) have greatly contributed to making the world what it is today, and scientists who have a passion to help and learn about our world are the key to a future that we would like to come true.

What if it were possible to bring back species long extinct?

Let the moa and the mammoth walk again? Or let a dinosaur once more paw the earth, or even make something new move and breathe? That power so often found in books or movies may soon not just be in our heads but in our hands.

New Zealand is a land of paddocks full of sheep, cows and chickens. If we were to
take a look at these creatures in the past, they would look quite different to the
domesticated version we are so used to. Through intensive selective breeding,
domesticated animals have been transformed so they better suit our needs; they
can produce more meat and grow more quickly. Breeding has also been used to
reduce infection and avoid diseases.

paddock with cattle &rainbow

 

Living on a farm myself, I can
easily see how our ideas and
inventions influence the land and
in turn influence our lives. This is
one way we have used scientific
methods in an attempt to create a
world which can better support us.

 

Modifying animals for our own purposes can be a terrifying and controversial concept, but human nature seems to dictate that we will continue to pursue this.

Genetic modification in the lab is different to intensive selective breeding but ultimately both are using science to change animals to suit us. De-extinction is a term that can be misleading, as we wouldn’t be able to bring back a creature that was extinct but rather create a hybrid with a close living relative, and so make a proxy of the extinct species. De-extinction is a concept that seems rather terrifying yet exciting. However, I wonder how different a creature made in this way would be from its ancestors, and I wouldn’t want to create a new creature that doesn’t fit into our world. An animal’s interaction with its environment is what influences its behaviour and quality of life. We may have to give ourselves limits on what we do, for the sake of our ethics; what would be the point of ‘bringing a species back to life’? Where would they live and how would they be able to survive in a world of humans, especially if humankind was a cause of their extinction?

The temptation to bring back species, or even help prevent endangered species from becoming extinct would be very great but I think we should be careful not to try and ‘rule’ over animals but rather do something that benefits the world as a whole and its future as well as humankind, especially when this science is not at all cheap. We may intend to help animal-kind as well as human-kind, but this technology may give us the feeling that we don’t have be proactive in protecting animals because we could always just bring back extinct species at will. Of course, I am talking about extreme circumstances and a future which may be more fitting in a sci-fi movie than reality but a version of this future could be real and may be not so far away.

In a world without science, there would be no new knowledge contributed to society, no inventions; the paddocks dotted with designer cows I see whenever I look out the window would not be possible. Science, and our understanding of it, has developed alongside the development of humankind. It is a part of me and my life, and the life of everyone who has ever wondered how something worked or used a cell-phone, turned on a light, or even just ate food cooked in a kitchen. Through science humans have developed the ability to influence genetic modification for our own purposes and technology is rapidly advancing right at this very moment.

We must always remember that our curiosity and scientific methods have made our present world and will make our future, but just because we have the power to genetically modify animals and humans doesn’t necessarily mean we should.

References
https://www.nzherald.co.nz/index.cfm?objectid=12039710&ref=twitter
http://www.dailymail.co.uk/sciencetech/article-3459168/From-giant-GM-salmon-buffed-Belgian-Bluecattle-animals-eat-looked-like-humans-began-breeding-food.html
https://en.wikipedia.org/wiki/History_of_genetic_engineering

Photo credits:

“A frightening and potentially dangerous technology”

Wednesday, May 13th, 2015 | STEPHEN BRONI | No Comments

That was how Otago University Prof Peter Dearden  from Genetics OtagoChinese genome scientist(1) described  a recent paper by a groups of chinese scientists describing the first genetically modified human embryos and opening a route to germ-line modification of our own species.

Check it out  and add your own views to the Sciblogs  comments  page.

Would you be willing to exchange your clothing for plumage?

Thursday, September 11th, 2014 | STEPHEN BRONI | No Comments

Ever heard of  ‘Transhumanism‘?Lucy Glendining sculpture of feathered child

Over the past few years, a new paradigm for thinking about humankind’s future has begun to take shape among some leading computer scientists, neuroscientists, nanotechnologists and researchers at the forefront of technological development.

 “Transhumanism”  is the name for a new way of thinking that challenges the premiss that the human condition is and will remain essentially unalterable.

 `Transhumanists’ say this  assumption no longer holds true. Arguably it has never been true. They argue that such innovations as speech, written language, printing, engines, modern medicine and computers have had a profound impact not just on how people live their lives, but on who and what they are.

What might happen in the next  20, 50, 100 years ?

A new book entitled  the The Proactionary Imperative presents a  the cultural, intellectual and ethical `justification’ for the emerging  transhumanist movement and in so doing paints an ethically  challenging and scary scenario for  the future of the human race?

“Fancy living forever, or uploading your mind to the net? The Proactionary Imperative embraces transhumanist dreams, but reminds why we need medical ethics”.

Calling all Biologists…Chemists…and maybe even Physicists

Tuesday, May 13th, 2014 | STEPHEN BRONI | No Comments

Daniel has posted a great question on  the
Knowledge Forum Biology Curriculum: Human Evolution   Discussion View:LifeSpiral2

Q: What are the best examples in the world today that support the
theory of evolution
?

 

I’m putting the challenge out there for you all.

This is a great opportunity to get back into Knowlege Forum with a topic at the heart of the biology curriculum.

Is the evidence all  from Biology? 

If you have forgotten how to log-in   to Knowledge Forum and build on a post we will be putting  up  a  link to refresher tutorial very soon but flick us an email in meantime and we’ll get you in there right away.

PS When you get into the  Knowledge Forum – Biology Curriculum: Human Evolution View you are looking the build-on the post  titled ‘Support’ on the far right of the Discussion View.

The Dawn of De-extinction. Are you ready?

Friday, March 15th, 2013 | STEPHEN BRONI | No Comments

“Throughout humankind’s history, we’ve driven species after species extinct: the passenger pigeon, the Eastern cougar, the dodo … A colour collage of threatened species

But now, says Stewart Brand, we have the technology (and the biology) to bring back species that humanity wiped out. So — should we? Which ones? ”

Check out  Stewart Brand’s TED  Talk here at

http://www.ted.com/talks/stewart_brand_the_dawn_of_de_extinction_are_you_ready.html 

 Is it the answer to every conservationist’s prayer?

Or,
As Barry Hillman  muses in  on one of  the responses,
“Sure, we have a responsibility to un-do the damage we’ve done,let’s try to change our thinking and become a more caring society that has no need to damage our world and then we can spend more of our valuable and limited time on earth creating instead of repairing.”

What do you think? 

There’s a follow-up here, a panel video discussion `hot off the  press’  from March 15th  :  http://tedxdeextinction.org/ 

(OUASSA students: You can now comment on our Blog-posts,  but after clicking ` Comment’ box, you will have to sign-in using your Otago University login given  to you at the January camp)

The Fish With A See-Through Head

Friday, October 19th, 2012 | STEPHEN BRONI | No Comments

 

Macropinna Microstoma: The Fish with a  See-Through HeadPhoto of deep sea fish  (Macropinna  Microstoma) with a transparent head

Every once in a while  (well, actually more often  than you might think) nature comes up with something so bizarre  it leaves you shaking your head and  pondering  “How? How? How?” and  puzzling  “Why? Why? Why?”

Found 600m or more down off the coast of California, the species lives in nearly total darkness. A transparent fluid-filled sack replaces the top of the head and two spots above the mouth, called nares, act somewhat like human nostrils, chemically sampling the water.

Experts think the fish hangs motionless in the current with its eyes swivelled upwards to spot the faint silhouettes of its prey. If it spots something it likes the look of, it rolls its eyes back to the forwards position and swims up to intercept it with its small, toothless mouth.

Check it out on this short video clip

Macropinna microstoma A deep-sea fish with a transparent head and tubular eyes

So, what’s the evolutionary advantage of a see-through head?
Would you want one for yourself?
( Might make wearing a beanie compulsory for some of us!)

Clambake Extinctions, Volcanic Deccan Pies & Demise of Dinosaurs

Friday, September 14th, 2012 | STEPHEN BRONI | No Comments

“Most researchers think the dinosaurs, many plants on land, and much of the life in thePainting showing dinosaur in landscape and comet hurtling through sky above sea succumbed to a huge cosmic impact 65.5 million years ago. But new evidence from the sea floor just off Antarctica points to a major extinction there a geologic moment before the impact. The culprit in this earlier cataclysm may well have been humongous volcanic eruptions in India—the same eruptions that some researchers have credited with wiping out the dinosaurs.”

Read the full story here
http://www.sciencemag.org/content/337/6100/1280.full

Gene mutation events linked to ‘milestones’ in human evolution

Wednesday, August 29th, 2012 | smida55p | No Comments

In the third online OUASSA biology tutorial I introduced the idea that a type of chromosomal mutation known as gene duplication may be important in “providing evolution some spare genes to play with”.

Many scientists think that gene duplications have contributed to some evolutionary changes, from the evolution of antifreeze proteins in polar fish (http://www.sciencedaily.com/releases/2011/01/110112122511.htm), the divesification of a group of calcium binding polypeptides in vertebrates that are important in tooth and bone formation and production of milk and salivary proteins in mammals (http://www.frontiersinzoology.com/content/2/1/15), to the evolution of true trichromatic colour vision in African apes. (http://anthro.palomar.edu/primate/color.htm; http://www.ncbi.nlm.nih.gov/pubmed/10413401).

A lovely example of the role of gene duplication in evolution for Level 3/Scholarship Biology – that is truly relevant to us all in the widest possible sense – can be found at http://www.newscientist.com/article/dn21777-the-humanity-switch-how-one-gene-made-us-brainier.html.  This article tells the story of how the repeated duplication of a gene involved in neural development may have been involved in two major advances in brain cell organisation and thinking power that correlate with some big leaps forward in our own biological evolution.  Enjoy!  Darren.

Great resource for Processes and Patterns of Evolution

Thursday, July 19th, 2012 | smida55p | No Comments

This is a one of my favourite websites for simple, clear and valid content for learning about evolutionary processes and patterns from Berkeley:

http://evolution.berkeley.edu/evosite/evo101/index.shtml

Heaps of wonderful images, explanations and examples for revision or note-taking.