The oystercatchers

I shall now look at them with new eyes indeed!  This article was linked by Thyagu in our MNS group, as a response to pictures and idying issues.

The incredible bill of the oystercatcher

Inspired both by the clam catches oystercatcher story, and by Greg Laden’s coverage of oystercatcher learning and predation behaviour, I thought it an opportune time to recycle the following from Tet Zoo ver 1. It originally appeared as one of my Ten Bird Meme posts of 2006…

One of my most favourite birds is the extraordinary, charismatic, beautifully interesting oystercatcher (meaing Eurasian oystercatcher Haematopus ostralegus: adjacent photo by Bjørn Christian Tørrissen, from wikipedia). One of ten or eleven extant haematopodid species, it sports pied plumage, pinkish legs, and has the heaviest bill of any extant wader. One of the most interesting things about oystercatchers is the fact that they exhibit resource polymorphism, with some populations exhibiting multiple different forms (Skúlason & Smith 1995). ‘Stabbers’ feed by jabbing their laterally compressed bill tips in between the valves of a mussel’s shell, while ‘hammerers’ crack open mussel shells by pounding on them. Some hammerers only break in to the shell on its dorsal side, while others only break in to the ventral side. Others attack only the left side valve, and others only the right valve. Other Eurasian oystercatchers are worm specialists with pointed tweezer-like bill tips. Superimposed on this variation is sexual dimorphism: females have longer, heavier bills than males (bill dimorphism of this sort is now known to be present in many birds) [image below, from Hosking & Hale (1983), shows a worm-eating bird on the left and a ‘hammerer’ on the right. There are other images that better show the variation (there’s a more impressive one in Sutherland (1987)), but I only have poor, very dark photocopies of them)].

First discovered by M. Norton-Griffiths during the 1960s (Norton-Griffiths 1967) – and extensively studied by a great many ornithologists since then – resource polymorphism among oystercatchers was initially thought to be learnt by the birds from their parents (and not genetically determined). It now seems that things are far more flexible, with individuals switching from one behaviour to the other over the years. It’s been said that juveniles can’t really learn how to handle prey from their parents given that many of them are reared inland and are abandoned by their parents before they ever get to the coast (Sutherland 1987). However, some oystercatcher adults that specialise on mussels spend up to 26 weeks teaching their young how to exploit prey (the long apprenticeship of the oystercatcher – longer in those that stab or smash mussels than in those that eat worms or exploit other prey – is well established in the literature: e.g., Wunderle (1991), Safriel et al. (1996)) [in the photo below, by John Haslam, from wikipedia, the adult has provided the juvenile with worms. The pointed tip on the adult’s bill shows that it’s a worm-catcher].

It seems that it’s the behavioural flexibility that controls bill shape, rather than the other way round, and another remarkable thing about oystercatchers is how specialized their bills are for coping with wear. Uniquely among waders, the bill grows at a jaw-dropping 0.4 mm per day (that’s three times faster than the growth rate of human fingernails). This rapid growth means that the bill can change shape very rapidly if the feeding style is changed, and captive individuals that were forced to switch from bivalve-feeding to a diet of lugworms changed from having chisel-shaped bills to tweezer-like bills within 10 days. A-maz-ing.

Given that oystercatchers are fairly large and powerful for waders, and able to smash open bivalve shells, it follows that they are formidable and potentially dangerous to other birds. Certainly males will chase off raptors when defending nesting females. I recall reading accounts of them caving in the heads of other waders during territorial disputes, but unfortunately I can’t remember where (a common problem, despite my well organized library). Most aggressive interactions recorded between oystercatchers, and between oystercatchers and other waders, involve piracy, and in fact some birds obtain most of their food this way, “attacking other birds at an average of five minute intervals during low tide” (Hammond & Pearson 1994, p. 61). As much as 60% of the food of some individuals is obtained by piracy. Finally, oystercatchers are incredibly long-lived, with the record-holder dying at age 35!* Now, come on, that is a truly extraordinary bird.

* Since I wrote this text, a Eurasian oystercatcher that reached the age of 40 has been reported.

For previous ‘Ten Bird Meme’ articles on Tet Zoo see…

• Ifrita the poisonous passerine
• Pseudopodoces, the corvid that wasn’t
• B. rex!
• Attack of the flying steamer ducks
• Fish owls in reverse

And for articles on bill morphology and function in birds see…

• The godwits’ many bills
• An encounter with a crossbill
• Coccothraustes: most bizarre of finches
• Sexual dimorphism in bird bills: commoner than we’d thought
• Woodpeckers: barbed tentacles and the avoidance of brain injury
• Mysterious channels of Alca torda
• Yes, it was a kiwi
• How to prevent cannibalism in pheasants
• The little-known subgenre of Talpanas tribute art

Refs – –

Hammond, N. & Pearson, B. 1994. Waders. Hamlyn, London.

Hosking, E. & Hale, W. G. 1983. Eric Hosking’s Waders. Pelham Books, London.

Norton-Griffiths, M. 1967. Some ecological aspects of the feeding behaviour of the Oystercatcher (Haematopus ostralegus) on the Edible Mussel (Mytilus edulis). Ibis109, 412-424

Safriel, U. N., Ens, B. J. & Kaiser, A. 1996. Rearing to independence. In Goss-Custard, J. D. (ed) The Oystercatcher: Individuals to Populations (Oxford University Press, Oxford), pp. 210-250.

Skúlason, S. & Smith, T. B. 1995. Resource polymorphisms in vertebrates. Trends in Ecology and Evolution 10, 366-370.

Sutherland, W. J. 1987. Why do animals specialize? Nature 325, 483-484.

Wunderle, J. M. 1991. Age-specific foraging proficiency in birds. In Power, D. M. (ed) Current Ornithology, Volume 8 (Springer), pp. 273-324.

China's Great Green Wall Helps Pull CO2 Out of Atmosphere - Scientific American

When we were in Rajasthan in January, we saw greening of various semi arid areas.  Locals mentioned that as compared to their childhood, these parts were actually greener, due to the arrival of canal water.

At that point I wondered, what this would mean for the macro environment.  How would this affect other green areas?  Would it draw rain from other geographies?

I have the same thought as I read this.  Interesting to see the long-term impact of this.

The point is, that there is no pressure on arid land, so it can be greened without human pressures, so China is building a bank of green space which may be the forest of the future!

China's Great Green Wall Helps Pull CO2 Out of Atmosphere

HONG KONG—After improving energy efficiency, piloting emissions trading and ramping up renewable energy expansion, China has also been moving on another frontier needed to help ease global warming.

According to a study published recently in the journal Nature Climate Change, the total amount of carbon stored in all living biomass above the soil has increased globally by almost 4 billion tons since 2003, with China contributing in a notable way to the increase.

"The increase in vegetation primarily came from a lucky combination of environmental and economic factors and massive tree-planting projects in China," said Liu Yi, the study's lead author, in a press release. Liu is a remote sensing scientist from the Centre of Excellence for Climate System Science at the University of New South Wales in Australia.

Liu noted that "[v]egetation increased on the savannas in Australia, Africa and South America as a result of increasing rainfall, while in Russia and former Soviet republics we have seen the regrowth of forests on abandoned farmland. China was the only country to intentionally increase its vegetation with tree planting projects."

In an email interview, Liu told ClimateWire that "the most apparent vegetation increase over China is observed in northern China, which is likely related to the Green Great Wall." Besides that, there has been some increase in vegetation in southeastern China, though there is no clue as to the cause of that increase, the scientist said.

China's Green Great Wall—formally known as the "Three-North Shelter Forest Programme"—is regarded by some experts as the largest ecological engineering project on the planet. Since 1978, at least 100,000 square miles of forests have been planted by Chinese citizens across the arid north, in an effort to hold back the creeping Gobi Desert. Once the project is completed in 2050, a massive belt of trees will stretch from northwestern China's Xinjiang through several northern regions to the country's northeastern part, Heilongjiang province.

Long-term impact is unclear
The introduction of the Green Great Wall, however, has doubters in the scientific community. Some scientists worry that planting trees where they do not grow naturally may do more harm than good, soaking up large amounts of valuable groundwater. Others question the mortality rate of trees planted there and whether these trees would negatively affect grass and shrubs, which in general are more resistant to drought and more effective at erosion control.

"The ecological issues are complex, and long-term results are not clear," said David Shankman, a professor emeritus of geography at the University of Alabama in Tuscaloosa, as well as a prominent critic of China's Green Great Wall project.

Liu, who cooperated with a team of international scientists tracking the changes in global vegetation, said that he does not have the full picture of the debate. "But from our satellite observations, we can see that the tree-planting project is able to increase the carbon stored in the vegetation standing above the ground, which can help remove some carbon dioxide from the atmosphere," Liu said.

The study shows that China's afforestation efforts, together with regrown forests in Russia and neighboring countries, offset roughly half of the carbon loss by tropical deforestation. While the world is getting greener as a whole, massive vegetation loss is still occurring in many regions, with the greatest decline to be seen on the edge of the Amazon forests and in the Indonesian provinces of Sumatra and Kalimantan.

Liu and his colleagues mapped changes in vegetation biomass using satellite measurements of changes in the radio-frequency radiation emitted from the Earth's surface, a technique called passive microwave remote sensing. The information was extracted from several satellites and merged into a one-time series covering the last two decades from 1993 to 2012.

Plants play a significant role in slowing down climate change, absorbing about a quarter of the carbon dioxide that people are putting into the air by burning fossil fuels and other activities. The study's authors say that although increased greenness means more absorption of carbon dioxide, the only way to diminish the impacts of global warming in the long term is to reduce the use of fossil fuels.

Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC. www.eenews.net, 202-628-6500