Fetal development: what about marsupials and birds?

Recently, I posted something about fetal heartbeats. In humans (and in mammals generally), oxygen and nutrients are transferred by the mother’s circulatory system to the placenta, and from there by the separate fetal circulatory system to where they are needed. As I noted in my earlier post, this process is functional in humans at about 21 days after conception.

In order for this process to work, the fetus obviously needs a beating, functional heart (although the heart continues to develop after it starts beating). It also requires a different kind of hemoglobin, which binds more tightly to oxygen than the mother’s hemoglobin does, thus facilitating oxygen transport across the placenta in one direction. Waste products, including carbon dioxide, are transported across the placenta in the other direction. The water-filled lungs, obviously, play no role in absorbing oxygen or getting rid of carbon dioxide.


Human fetal circulatory system, showing the ductus venosus and ductus arteriosus which partially divert blood away from the liver and the water-filled lungs (from American Heart Association)

There are alternatives to this placental system, however. Marsupials, such as kangaroos, do not have the same kind of placenta. Kangaroos are therefore not able to survive in the womb longer than about a month. Instead, they are born in a partially developed state, and crawl to the pouch, where they complete their development drinking milk and breathing air with their still-developing lungs.


Young joey (baby kangaroo) in its mother’s pouch (photo by Geoff Shaw)

Birds have yet another approach, developing inside an egg. Nutrients are packaged inside the egg along with the embryo. Oxygen and carbon dioxide diffuse in and out through the eggshell, and oxygen is absorbed by the embryo through the allantois. The allantois also acts as a dumping ground for nitrogenous waste. When the nutrients in the egg are exhausted, it is time for the bird to hatch.


Chicken embryo on its 9th day (image by KDS4444)


The Cascades Raptor Center


The Cascades Raptor Center, Eugene, Oregon (image credit)

I am currently travelling in the US, and recently dropped in at the Cascades Raptor Center in Eugene, Oregon (see the Raptor Center website and Raptor Center instagram). This is primarily a hospital and rehabilitation centre for injured raptors (eagles, hawks, falcons, ospreys, owls, vultures, etc.). By my count, 37 birds are on public display in wire mesh aviaries (mostly birds too seriously injured to be released).

Admission is US$10 per adult, and there is a small gift shop. Viewing the birds takes about an hour, and I really enjoyed my visit (the Center would also appeal to children of all ages). Tripadvisor gives the Center 4½ stars, which is probably a little more than I would give, given the Center’s size (but the money supports the Center’s work). There are also more interactive night-time viewing events, which I did not experience.


Ferruginous hawk (Buteo regalis) and Gyrfalcon (Falco rusticolus) at the Raptor Center (photographs by Anthony Dekker)


Vesper Flights: a book review and reflection


Vesper Flights by Helen Macdonald

I have been waiting eagerly for a copy of Vesper Flights by Helen Macdonald. If you have read my review of her H is for Hawk, you will understand why. Early reviews of the new book were also positive – “powerful essays,” said The Guardian; “soul-stirring,” said USA Today; “a beautiful and generous book,” said npr. The Goodreads community gave it 4.2 out of 5.

I was fortunate enough to get a copy of Vesper Flights for Christmas. It is a collection of 41 essays, and Helen Macdonald writes “I hope that this book works a little like a Wunderkammer. It is full of strange things and it is concerned with the quality of wonder.” Many of the essays have an autobiographical component. Several moved me to tears.


A Wunderkammer painted by Domenico Remps around 1695 (click images in this review to zoom)

The essays in the collection are:

  1. Nests – a reflection on bird’s nests
  2. Nothing Like a Pig – coming face-to-face with a wild boar
  3. Inspector Calls – a beautifully written and touching account of an autistic boy meeting a parrot
  4. Field Guides – a visit to Australia, and praise for field guides

The hairpin banksia gets a mention in essay #4

  1. Tekels Park – reminiscences of a childhood spent among nature in Tekels Park
  2. High-Rise – a wonderful account of the surprising amount of life that can be found in the night-time sky
  3. The Human Flock – about migration
  4. The Student’s Tale – about a refugee
  5. Ants – about nuptial flights in ants

A winged queen ant (photo credit)

  1. Symptomatic – about migraines and impending doom
  2. Sex, Death, Mushrooms – “Many toxic fungi closely resemble edible ones, and differentiating each from each requires careful examination, dogged determination and often the inspection of spores stained and measured under a microscope slide.
  3. Winter Woods – walking through woods in the winter
  4. Eclipse – an eclipse is an emotional experience
  5. In Her Orbit – with Nathalie Cabrol in the Atacama Desert, site of the now-defunct Carrera Solar Atacama (this chapter is based on a New York Times article)

San Pedro de Atacama, Chile (photo credit)

  1. Hares
  2. Lost, But Catching Up
  3. Swan Uppingswan upping on the Thames as social commentary
  4. Nestboxes – are they for the birds, for us, or both?
  5. Deer in the Headlights – this essay highlights the problem of deer-vehicle collisions (the UK gets about 1 per thousand people per year); Australia has a kangaroo-vehicle collision problem of similar magnitude, but that issue is perhaps viewed a little differently
  6. The Falcon and the Tower – about urban peregrine falcons, specifically in Dublin (see also this short documentary film)

The towers of the decommissioned Poolbeg Generating Station in Dublin, with a magnification of the western (leftmost) tower. These towers, around 207 m high, are home to the peregrine falcons described in essay #20 (photo credit)

  1. Vesper Flights – the central and title essay, based on a New York Times article, is about swifts
  2. In Spight of Prisons – all about glow-worms, Lampyris noctiluca
  3. Sun Birds and Cashmere Spheresgolden orioles and bearded reedlings
  4. The Observatory – “a swan had come towards me and offered me strange
    companionship at a time when I thought loneliness was all I could feel.
  5. WickenWicken and other fens, which I imagine inspired the home of Puddleglum in the Narnia stories

A hide at Wicken Fen (photo credit)

  1. Storm
  2. Murmurations – “Words to accompany Sarah Wood’s 2015 film Murmuration x 10
  3. A Cuckoo in the House – about cuckoos and the man who inspired the character ‘M.’ Yes, that ‘M.’
  4. The Arrow-Stork – the arrow-stork and the study of bird & animal migration
  5. Ashes – on tree diseases
  6. A Handful of Corn – as a famous song says: “Come feed the little birds, show them you care, and you’ll be glad if you do; their young ones are hungry, their nests are so bare, all it takes is tuppence from you.

  1. Berries
  2. Cherry Stones
  3. Birds, Tabled – a fascinating exploration of the morality of bird-watching versus bird-keeping and the class conflicts involved (a number of reviewers online have taken issue with this chapter, specifically)
  4. Hiding
  5. Eulogy
  6. Rescue – a beautiful account of bird rescue and wildlife rehabilitation
  7. Goats
  8. Dispatches from the Valleys – a heavily autobiographical chapter, raising all kinds of spiritual questions (but not really answering them)
  9. The Numinous Ordinary – “I kept trying to find the right words to describe certain experiences and failing. My secular lexicon didn’t capture what they were like. You’ve probably had such experiences yourself – times in which the world stutters, turns and fills with unexpected meaning.
  10. What Animals Taught Me – “When I was a child I’d assumed animals were just like me. Later I thought I could escape myself by pretending I was an animal. Both were founded on the same mistake. For the deepest lesson animals have taught me is how easily and unconsciously we see other lives as mirrors of our own.

Not surprisingly, about half the chapters in this book are about birds, in some way or other:

At its best, this book is as good as the superb H is for Hawk, but is not consistently so (indeed, it scarcely could be). While some of the chapters are truly wonderful, others have a moralistic tone that I thought was a little more heavy-handed than it needed to be, and which became a little repetitive after a while. In the last chapter Helen Macdonald offers a corrective: “These days I take emotional solace from knowing that animals are not like me, that their lives are not about us at all.” Or, as C.S. Lewis once put it:

Come out, look back, and then you will see … this astonishing cataract of bears, babies, and bananas: this immoderate deluge of atoms, orchids, oranges, cancers, canaries, fleas, gases, tornadoes and toads. How could you ever have thought this was the ultimate reality? How could you ever have thought that it was merely a stage-set for the moral drama of men and women? She is herself. Offer her neither worship nor contempt. Meet her and know her. If we are immortal, and if she is doomed (as the scientists tell us) to run down and die, we shall miss this half-shy and half-flamboyant creature, this ogress, this hoyden, this incorrigible fairy, this dumb witch.

Helen Macdonald has a genuine talent for showing the reader what she saw, and the reader of a book like this will feel appropriate things in that situation. Perhaps the more moralistic tone is the inevitable, and possibly appropriate, nature of an essay written for a newspaper or magazine. The fact that this book is a collection of such essays would then explain why it feels a little repetitive at times.

My recommendation: buy this book, but only read a few chapters each week. And think about them.

* * * *
Vesper Flights by Helen Macdonald: 4 stars


Fibonacci and his birds (solution)

In the previous post, we described Fibonacci’s “problem of the birds” (“the problem of the man who buys thirty birds of three kinds for 30 denari”). In English:

“A man buys 30 birds of three kinds (partridges, doves, and sparrows) for 30 denari. He buys a partridge for 3 denari, a dove for 2 denari, and 2 sparrows for 1 denaro, that is, 1 sparrow for ½ denaro. How many birds of each kind does he buy?”

The man must buy at least one of each kind of bird, or he wouldn’t be buying “birds of three kinds.” Also, he must buy less than 10 partridges, because 10 partridges (at 3 denari each) would use up all his money. Similarly, he must buy less than 15 doves. We can thus make up a table of possible solutions:

Of those 126 possible solutions, only one works out correctly in terms of cost, and that’s the answer. But that’s an unbelievably tedious way of getting the answer, and you’d be rather foolish to try to solve the problem that way. The obvious approach is to use algebra. Write p for the number of partridges bought, d for the number of doves, and s for the number of sparrows. Because the man buys 30 birds, we have the equation:

p + d + s = 30

And because the costs add up to 30 denari, we have:

3 p + 2 d + ½ s = 30

Doubling that second equation gets rid of the annoying fraction:

6 p + 4 d + s = 60

If you’ve done any high school algebra, no doubt you want to subtract the first equation from this, which will eliminate the variable s:

5 p + 3 d = 30

But now what? That gives a relationship between the variables p and d, but there doesn’t seem to be enough information to get specific values for those variables.

Fibonacci solves the problem a different way. His solution is based on a key insight – the man buys 30 birds for 30 denari, so that the birds cost, on average, 1 denaro each. Fibonacci then makes up “packages” of birds averaging 1 denaro each. There are only two ways of doing this. Package A has 1 partridge and 4 sparrows (5 birds for 5 denari), and package B has 1 dove and 2 sparrows (3 birds for 3 denari). The solution will be a combination of those two packages.

Now the man can take 1, 2, 3, 4, or 5 copies of package A, leaving 25, 20, 15, 10, or 5 birds to be made up of package B. But the birds making up package B must be multiple of 3, so that the only possible answer is 3 copies of package A and 5 copies of package B. This means that the man buys 3 partridges, 5 doves, and 3×4 + 5×2 = 22 sparrows. That’s 30 birds and 3×3 + 2×5 + ½×22 = 30 denari.

Now it turns out that, had we kept on going with the algebraic approach, we would have gotten the same answer. We had:

5 p + 3 d = 30

Given that the numbers of partridges and doves (p and d) had to be positive whole numbers, that meant that p had to be a multiple of 3, and d a multiple of 5. That could only be achieved with p = 3 and d = 5.

We can also return to the diagrammatic approach. The equation:

5 p + 3 d = 30

describes the diagonal red line in the diagram below. That line only crosses one of the possible solutions, namely the dot corresponding to 3 partridges and 5 doves.

In mathematics, there’s more than one way to skin a cat. Or, in this case, a bird.


Fibonacci and his birds

The mathematician Leonardo of Pisa (better known as Fibonacci) is famous for his rabbits, but I was recently reminded of his “problem of the birds” or “the problem of the man who buys thirty birds of three kinds for 30 denari.” This problem appears in his influential book, the Liber Abaci.

The “problem of the birds” is expressed in terms of Italian currency of the time – 12 denari (singular: denaro) made up a soldo, and 20 soldi made up a lira. In the original Latin, the problem reads:

“Quidam emit aves 30 pro denariis 30. In quibus fuerunt perdices, columbe, et passeres: perdices vero emit denariis 3, columba denariis 2, et passeres 2 pro denario 1, scilicet passer 1 pro denariis ½. Queritur quot aves emit de unoquoque genere.”

In English, that translates to:

“A man buys 30 birds of three kinds (partridges, doves, and sparrows) for 30 denari. He buys a partridge for 3 denari, a dove for 2 denari, and 2 sparrows for 1 denaro, that is, 1 sparrow for ½ denaro. How many birds of each kind does he buy?”

How many birds of each kind does the man buy? It may help to cut out and play with the bird tokens below (click image to zoom). In a similar vein, what if the man buys birds as follows (still purchasing birds of all three kinds, and at the same price)?

  • 4 birds for 6 denari
  • between 6 and 10 birds for twice as many denari as birds
  • 8, 11, 13–14, 16–22, 24–25, or 27 birds for the same number of denari as birds
  • 8 birds for 12 denari
  • 12 birds for 18 denari
  • 16 birds for 12 denari
  • 28 birds for 21 denari
  • 6, 8–9, or 14 birds for 11 denari
  • 7–10, 12, 15, or 18 birds for 13 denari

Solution to the main problem here.


A new species of thrush for 2016

The Himalayan forest thrush (Zoothera salimalii – photo by Craig Brelsford above) is a newly described species of bird. It was formerly grouped with Z. mollissima, which breeds above the tree line. In contrast, Z. salimalii breeds in coniferous forests up to the tree line, from Tibet to Vietnam. In addition, Z. salimalii has a different song from its alpine cousin, as well as differing genetically. This is enough to make it a distinct species.

With improvements in technologies for DNA and other analyses, we are starting to see many such new species “carved out” of existing ones.


Creating an Australian Feather Map


Photo: Louise Docker, 2007

Australian scientists are encouraging people to collect feathers found on the ground or in the water in wetlands (with details of where they were collected). After analysis using mass spectrometry and high resolution X-ray fluorescence, a feather map will be constructed. All aspiring citizen scientists, young and old, can get involved and follow the project on Instagram. It looks like a great way to monitor bird populations in wetlands!


World Solar Challenge: Weather in Darwin

One very helpful input to race strategy in a solar car race is weather expertise. How much sunshine can we expect? And when can we expect it? In 2013, Solar Team Twente took along an expert from the Joint Meteorological Group of the Royal Netherlands Air Force to help with that. This year, Punch Powertrain Solar Team (team 8) is taking along an expert from the the Royal Meteorological Institute of Belgium, who will be blogging his insights and experiences.

For those without his specialist expertise, forget everything you thought you knew about Spring and Summer, Autumn and Winter. Darwin has 7 seasons, as the Larrakia People tell us, and the World Solar Challenge begins towards the end of Dalirrgang (the “Build Up” – click image above for multimedia tutorial). Dalirrgang is a kind of overture to the rainy season (the “Wet”). Traditionally, Dalirrgang is the time to hunt the Magpie goose (photo by Djambalawa below).

Long-term weather forecasts suggest that the World Solar Challenge this year might in fact begin on a partly sunny day, with a little rain, but that’s very uncertain, this far ahead.

Visiting Vanuatu

Recently I took my own advice and visited the island nation of Vanuatu. I had a great time! Since the islands are volcanic and surrounded by coral reefs, the beach sand ranges from pure white to basaltic black, with an intermediate grey-brown in some cases, like the beach in my photo above.

Vanuatu has a range of interesting wildlife (though no native land mammals other than bats). Birds of Vanuatu include the Vanuatu kingfisher (Todiramphus farquhari, above), which I did not see. There are 120 other bird species, including visiting seabirds. Butterflies of Vanuatu (of which I saw many) include the Monarch butterfly (Danaus plexippus) and several subspecies of the Canopus Swallowtail (Papilio fuscus, below).

Underwater, Vanuatu provides wonderful opportunities to see marine life while diving or snorkelling. The Flickr photographs below are by Diane Brook (click images to zoom):