Jetting from London to Houston, with noise cancelling headphones isolating me from both a snoring neighbour and the rumble of our propulsion, I imagined a Bantu throwing a spear at a stork. I also wondered what it was like in 1822 when no one could imagine a White Stork making an annual round trip after breeding in Germany, going south of the equator in East Africa to avoid European winters. At that stage in our understanding, the ancient Greek idea that birds turned into fish for the winter was still popular.
A friend who was far more kinetically elite than me had recently recommended I listen to the BBC In Our Time podcasts rather than the boring, please-most offerings on transcontinental flights. That day in 2018, I was listening to Bird Migration among 250 people while crossing the Atlantic some 10,000 metres above the sea travelling at 700 km per hour. We ate and slept on the wing.
- In Our Time website has improved substantially of late. Here’s a string of facts from the original podcast.
- Derek Mooney had a Mooney Goes Wild episode on RTE in which there is a picture of the same stork with the Bantu spear I was hearing about. This was not the only African speared Stork found in Germany.
Globally, some 4,000 species of bird are migrants. Some 40 per cent of the world’s total. Several hundreds of millions of birds. Cornell host BirdCast where you can watch the North American birds in migration by webcast courtesy of the weather surveillance radar network that has also been detecting/tracking birds for over seven decades.
Despite acute interest, we appear to understand a lot less about bird migration than you might imagine.
I had no idea that some birds consume their livers and gonads as they migrate which they regenerate when they need them again. This saves weight in addition to providing energy.
I was listening to the podcast again this weekend as I was painting a fence and a shed. I was being watched by robins (some of whom migrate), wrens and magpies (none of whom migrate).
I’d looked into bird migration over the last few months because I’d noticed there were very few swifts flying above house. I have a memory, romantic perhaps, of many swifts crying as they hunted in large numbers for insects above our house. Then I found a RSPB web page that says swifts are in trouble. It appears that UK swifts have declined by 53% over the last two decades. My anecdotal observation roughly fits with that alarming headline.
Some studies say that 80% of juveniles of some species die on migration. Bats are among their predators.
Other studies suggest that the survivors who migrate live longer than the residents that don’t.
Yet other studies are looking into how much of migration craft is inherited. Apart from navigation unknowns, how do they know where to to go? The juveniles of many species set out long after their parents have departed.
Or how do they know when to set out? This is especially important for those going to the high arctic where the breeding period is just a couple of weeks.
Smell is increasingly of interest to academics studying bird migration. Remove the avians olfactory sense and the affected birds don’t make it home.
Magnetic fields are important too. Cover the correct eye of a pigeon and they’ll probably get lost. It may be that an eye protein called a cryptochrome enables magnetoreception which itself is dependent on blue light. Pigeons also have some magnetite in their beaks. The two probably work in concert.
Migration is predominantly used by birds that breed in the northern hemisphere. There are inter-continental land bridges that facilitate flyways for hundreds of millions of birds across the Levant, the straits of Gibraltar and between the Americas. And there are the three Asian flyways where rates of species decline of up to 8% per year are among the highest of any ecological system of the planet.
Could the birds that do oceanic navigation be a place to focus study? I’ve mentioned the skills of albatrosses before. I’ve also written about Tim Birkhead’s Bird Sense (2012) and I’m reminded now of a bar-tailed godwit that travelled 11,000 km in eight days.
It seems there are many sense technologies in play but it also appears that the senses can be used in a hierarchical way. In computerese, we write macros to do 95% of the work so we can spend 95% of the time solving the remaining 5% of the problem. Birds only need to be accurate with one and then resolve for precision using multiple technologies. Magnetics could guide a bird from Norway to Africa but it might need olfactory and other cues to complete the journey.
Melvyn Bragg asked if the complexity of the ‘technology’ of bird senses could be compared to the technologies being developed in Silicon Valley. The panel was divided on their opinion but I think I side with guest Barbara Helm who thinks it’s ‘dauntingly complex’.
Well I never thought I’d read that a bird can eat its own liver and gonads, and then regrow them. There’s something weird about eating parts of oneself and then growing those parts back.
Declining swifts are another real concern. Are they the canaries in the coal mine?
Belinda O’Byrne says
What do the female birds consume in place of gonads?
Simon Robinson says
Gonads are generic reproductive organs, both testes and ovaries.
Autophagy is the technical term for consuming yourself.
There’s a godwit that absorbs up to 25 percent its liver, kidneys, and even the alimentary canal.
I was going to mention that some birds (types of geese and ducks) migrate at altitudes of 8,000 m where they should die from the lack of oxygen (hypoxia). I find this story of adaptation even more incredible than the autophagy of the gonads.
Adapt to survive!