About Me

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Canberra-based naturalist, conservationist, educator since 1980. I’m passionate about the natural world (especially the southern hemisphere), and trying to understand it and to share such understandings. To that aim I’ve written several books (most recently 'Birds in Their Habitats' and 'Australian Bird Names; origins and meanings'), run tours all over Australia, and for the last decade to South America, done a lot of ABC radio work, chaired a government environmental advisory committee and taught many adult education classes – and of course presented this blog, since 2012. I am the recipient of the Australian Natural History Medallion, the Australian Plants Award and most recently a Medal of the Order of Australia for ‘services to conservation and the environment’. I live happily in suburban Duffy with my partner Louise surrounded by a dense native garden and lots of birds.

Thursday, 15 January 2015

I Come, I Soar, I Conquer

It's been a while now since I waxed lyrical about the amazing spin-off of flight called hovering. It is an extraordinary achievement, but there is another extreme to flying that only a very few species have ever achieved. 
Female Magnificent Frigatebird Fregata magnificens, Galápagos.
She accompanied our boat (with many companions - see below) for kilometres,
and I don't recall once seeing her flap.

Strictly, she was not flying, but soaring. Perhaps this is being a bit precious, but it does seem important to make the distinction or we'll miss out on understanding this extreme of flight. Flying is, in technical terms, 'assisted aerial motion', which can also be stated as 'flapping your wings'. You need to be able to flap fast enough to overcome the drag of air along and behind your body. To accelerate or climb you must flap even faster still. 

Soaring however, as I observed in the caption above, involves not flapping your wings. The energy in this case comes from the air around you, which may be deflected up (eg from a boat pushing through it, or from an air mass moving over a ridge-line or a mountain) or from rising thermals of warmed air, over a sand dune or even a city. The frigatebirds were using this energy to move forwards; birds which rise on a thermal can then soar for tens or even hundreds of kilometres, losing height only incrementally as they go. In any case, as you could imagine, very complex and precise adaptations of both physiology and shape are required; it seems that only some larger birds and pterosaurs have ever mastered the art. (I should emphasise that pterosaurs had no connection to birds; they were reptiles of an entirely different line from the dinosaurs which gave rise to birds. Or perhaps I should say the group of living dinosaurs that we call birds.)

Mathematically, the best shape for a soaring wing is the one exhibited by the frigatebirds above; it is very long and slender and pointed, and known in the trade as a 'high aspect ratio' wing. Aspect ratio is defined as wingspan squared divided by wing area - in other words a high aspect ratio means a very low wing loading, or very little weight per square centimetre of wing. This allows very slow flight without stalling, and facilitates 'riding the wind'. (It's also good for hovering, but that's another story.)

Waved Albatross Phoebastria irrorata. Española, Galápagos.
Albatrosses are also consummate soarers and utilise high aspect ratio wings.
However, everything in nature is about trade-offs and compromises, and most soaring birds do not have these very long slender wings.
Straw-necked Ibis Threskiornis spinicollis soaring, Grenfell, New South Wales.
(I love the way the two birds on the left are undertaking running repairs to their feathers.)

These ibis are soaring on very differently shaped wings from the ideal. The problem with the high aspect ratio wings is not with their undoubted efficiency in the air, but the problems they pose in getting there. Simply, they are so long that a normal takeoff is very difficult to achieve; they bang on the ground when being flapped! Large birds which possess them must either launch into the air from a high point (such as a cliff, which is what the Waved Albatross on Española were doing) or using wind energy to get into the air (which both albatrosses and frigatebirds also so).

The ibis use the compromise solution, known somewhat inelegantly but descriptively as 'soaring wings with slots'. These wings are broad and long, with deep slots between each primary feather to reduce air turbulence around the wing tips and promote easy soaring. While slightly less efficient than the albatross wing, they are shorter and enable relatively easy takeoff from the ground. 

Not only is soaring only effectively available to large birds (and formerly pterosaurs), because only they can have the large wing area to body weight ratio required, but the reverse is true too. As birds get closer to the cut-off maximum flying weight of around 15kg (the largest eagle, swan, condor, pelican, albatross and bustard are all about this size), soaring becomes the only realistic option, as sustained powered flight would be just too energy-intensive.

And with that, let's end by simply admiring some other magnificent soarers. 
Black-breasted Buzzard Hamirostra melanosternon, Uluru, central Australia.
Many soaring birds have black wingtips, because the melanin confers resistance to wear.
Andean Condor Vultur gryphus, Los Glaciares NP, Argentina.
One of the great soarers!
Galápagos Hawk Buteo galapagoensis, Santiago, Galápagos.
White-bellied Sea Eagle Haliaeetus leucogaster, Esperance, Western Australia.
A magnificent sight soaring along coastlines (and sometimes well inland) from India to southern Australia.
Little Eagle Hieraaetus morphnoides, Great Sandy Desert.

American Swallow-tailed Kite Elanoides forficatus, Ecuador.
One of the smaller soarers but an efficient one,
which in part uses the skill to glean prey from foliage.
Black-necked Stork Ephippiorhynchus asiaticus, Cobbold Station, north Queensland.

Australian Pelicans Pelecanus conspicillatus, Longreach Waterhole, Northern Territory.
Pelicans constantly criss-cross the continent by using rising thermals, especially over sand dunes.

Soaring, just another wonderful aspect of this wonderful world, and perhaps one we don't think about enough.



David McDonald said...

Thanks Ian, fascinating, and beautiful photos.

A question, perhaps for another post: why do some birds (especially raptors?) have 'fingers' at their wing-tips, and others do not?

Kath H said...

Thanks Ian. It is about time to say how much I enjoy your posts and this one was illuminating. I was very interested in the two on Cameroon having met a nun from there recently, too briefly to talk about her country.

Ian Fraser said...

David, good to hear from you; you are always very kind. I think your question belongs exactly here; the 'fingers' are formed by the slots between the primaries, so they are indicators of soaring and hovering birds. They are controllable however, so a kestrel for instance shows fingers when hovering, but not when flying along. Ditto a Wedgie.

Kath, I'm so glad you took the trouble to write - it means a lot to me. After writing the Cameroon postings I needed to do something less depressing, and talking about flying (and soaring!) birds uplifts me.

Susan said...

Lovely. I have very fond memories of many soaring birds -- pelicans in Australia, gannets while crossing the English Channel on the ferry, buzzards over my orchard and butterfly transects here in France and of course here everyone greets the annual migration of the cranes and storks with excitement. 'Did you see the cranes yesterday?' is always a good conversation opener in March or November when you run into someone in the street.

Ian Fraser said...

Thanks Susan, and good to hear from you too; I hope your year has started well. Yes, I find it very uplifting to watch and contemplate soaring birds (and no, I'm not trying to be cute). Unfortunately the storks and cranes don't come to us here, so tomorrow we're flying to Darwin to visit them (and family...).

Berigora said...

Ian, This morning Frank (A) and I were just saying how we miss your Whimsy, and here is one by another name. Wing form and function was a very interesting subject during my ornithology course at CSU. Just one point, on a note of possible ambiguity, of course pterosaurs were not related to birds.

Ian Fraser said...

Thanks A (or B), it's nice to hear that someone thinks about the Whimsies! I stopped them because I rarely had any real sense anyone was reading them; I find this more satisfying in that I can see how many people are interested. Sorry for your sake they can't all be about birds - your mind will have to get out more... Thanks for the note about the pterosaurs; I've now clarified that.

Flabmeister said...

Some years ago a COG talk addressed the question "What do a million migrating eagles eat" referring to the annual movement of Short-toed Eagles through the Jordan Valley. The answer was "Nothing" as, by soaring, their flight was so energy efficient they didn't need to eat.

The happy wanderer. said...

One of the reasons I enjoy blogging is that I learn odd bits and pieces - this time about the black wing tips! I have Wedge-tailed Eagles near by at times and love watching them "thermalling".