One of the most recurring assumptions relating to over water bird migration is that the vast expanse of the seas and oceans are devoid of the visual landmarks we humans regard as necessary to find our way. Therefore birds also would be unable to navigate visually and so they would therefore have some super ability to navigate using the earth’s magnetic field and the stars.
A Bar-tailed Godwit in flight. Like many birds their feathers provide a beautiful pattern. The pattern however may provide the means by which they navigate.
It’s not surprising really that we assume the seas are featureless. Just about any map that we pick up depicts the oceans as empty blue spaces between landmasses. Our history of navigation that was predominated by ships reinforces this assumption. From the deck of a ship the sea all looks pretty much the same.
Birds that fly over the oceans, funnily enough, have a birds-eye-view and it’s a completely different perspective.
So lets pretend once again that we are flying our little aeroplane from Alaska to New Zealand and somewhere out of sight but not far away, E7 the magnificent Bar-tailed Godwit is doing the same.
High up above us an airliner is winging its way across the Pacific using a state-of-the-art Flight Management System which gets its navigation information from a combination of inertial navigation systems and multiple GPS. For these pilots navigation is precise and reliable. Not surprisingly nowadays, the pilots of these aircraft are largely oblivious to the visual cues beneath them.
But up to the introduction of inertial navigation equipment and GPS flight across the ocean was not so plane sailing, particularly in light aircraft. By today’s standards pilots relied on navigation equipment that was alarmingly crude.
Like E7, many of these flights crossed the Pacific Ocean between North America and New Zealand. There were a small bunch of intrepid aviators delivering small single and twin-engined light aircraft from their manufacturers in the US whose efforts are largely unknown. They flew the long non-stop flight between California and Hawaii and then island hopped the rest of the way. Other small agricultural aircraft that were manufactured in New Zealand went in the reverse direction.
Many light agricultural aircraft such as this DHC Beaver were flown both directions between the USA and New Zealand. They relied on basic navigation, luck and a sharp eye to avoid disappearing in the Pacific Ocean. Not all of them made it!
These small aircraft were almost always flown by a single pilot crammed into his or her seat with every other bit of available space taken up with extra fuel tanks. They had the most basic of navigation equipment. The most they had was a chart with the great circle route plotted, a compass and a blind faith that they would come within receiving range of a radio beacon that could guide them in to their often small remote destinations. Radio beacons that were often switched off, unserviceable or of such low power that they had to be almost within sight of their destination before it would be of any use. By necessity, those pilots learned techniques based on visual observation of the sea and the clouds to help them find small atolls in the middle of wide blue ocean where they needed to refuel and break their journeys.
If there is one thing that birds are very good at it is their vision and observational abilities. The anatomy of birds’ eyes and the light spectrum they can perceive is different to ours and that gives them abilities we humans are unaware. Their whole lives are dependent on acute eyesight and mental visual pictures of their world… for foraging, reproduction, defence, avoiding crashing into things while flying… after all when you travel at the speeds birds do their whole observation, processing and manoeuvring systems need to be super fast and precise to avoid being eaten, to dodge between trees, branches, buildings, fast moving cars, wind generators and even to land on branch or telephone wire without crashing… and last but not least, their vision is used for navigation. Not only are they seeing things that we can’t see, but also they are recognising and using visual information that we ignore or think is insignificant.
Australian Pelicans rest on a brackish coastal lake west of Dili in Timor Leste. Birds migration maybe seasonal or just in response to local conditions. When these birds were photographed in February 2008 Australia was in one of its worst droughts in recent history.
Surfboard riders flock to the islands of Indonesia. Along the south west coasts of Bali and the island chains off Sumatra waves break on the reefs and headlands with a consistent regularity that makes this beautiful part of the world a surfer’s Mecca. Warm tropical seas, consistent surf and cheap living… I’m packing now… and lots of interesting bird life.
The waves that surfers travel from all over the world to surf on are not generated in Indonesia. They are born deep in the southern oceans by the consistent gales in the roaring forties and fifties and travel thousands of miles across the Indian Ocean before colliding with the coasts of Indonesia. Similarly swells generated in the high latitudes travel across the Pacific from both north and south.
Flying south from the bottom of New Zealand into the southern ocean to oil rigs I have witnessed these giants of the sea. The swells are long and large, deceptively ponderous and are never absent even on the rare calm days. These immensely stable swells contain millions of tons of inertia and travel in consistent lines of constant direction that change little as they travel. They are stable patterns that remain the same from year to year. Although local winds and storms may produce a confusion of conflicting sea patterns above, the underlying swells continue on unchanged beneath the turmoil. From the air they are unfailingly discernible.
A Royal New Zealand Air Force Iroquois helicopter flying over the reef on the southern side of the Fijian island of Vitu Levu. An endless progression of swells that originate in the southern oceans breaks on the reef. Fiji, as well as a good birding destination is a consistently good surfing spot.
Having spent many hours flying above the oceans from the tropics to the sub arctic, I observe these swell patterns regularly. Even a glassy smooth tropical sea has long slightly darker lines that giving away their presence. And because they are so consistent they provide a directional matrix on the surface of the sea. Birds only need to measure their angle against these lines and they have a consistent steering guide. And most beneficially these swell patterns follow direct paths across the ocean. None of the problems, as discussed in my earlier posts on navigation, regarding the vagaries of magnetic variation and the complexity of calculating the compass directions required to maintain great circle tracks exist. The swells are geographically orientated and have no magnetic influences.
Birds use these visual grid lines to provide them with the steering information as well as compensating for the effects of the wind. Many birds, and the bar-tailed Godwit in particular have beautiful patterns on their wings, tails and bodies, often consisting of bars and angled lines – hence Bar-tailed Godwit. Observing these feather patterns on fellow birds at close proximity with each other within the flock in relation to the swell lines may well provide them the method of assessing the angle they need to maintain a steady track as well as working out whether the wind is blowing them off track.
If we look back to our early aviation pioneers we can see how some airborne navigators used the texture on the surface of the sea (and the land) to help find how much they were drifting off track caused by the wind. They had a simple yet effective doohickie called a drift sight. It was basically a tube the navigator could look through vertically at the surface of the sea. It had a series of parallel lines on a lens that could be rotated. The navigator rotated the tube until the lines followed the texture of the surface of the sea. The difference in angle between the lines and fore and aft axis of the aircraft was the drift angle.
So birds, by using the barring patterns of their neighbours wings and tails as reference lines, can judge not only the angle of the swells to which they need to fly but also how much the winds is blowing them off track. Using this information they know which heading to fly and to compensate for the wind.
Black-tailed Godwits in Timor Leste. Like their cousins the Bar-tailed, these migrants also have distinctive wing and tail patterns.
Unlike the sun and stars, observing swell patterns are not blocked out by cloud. And using their excellent night and UV vision, birds can see the swell patterns just as well at night and possibly by using phosphorescent footprints on the surface of the sea.
But, as discussed in previous posts; using steering information such as swell patterns is dead reckoning and only part of the navigation process. Birds still need position fixes to confirm they are going in the right direction and to be able to correct for any errors that have crept in. So what other features are observable on the so-called featureless oceans. Well mostly there are clues on the clouds and sea surface itself.
Over the sea clouds tend to build up over land. Even a sand bank such as this one in the Timor Sea can provide sufficient day time heat to trigger a cumulonimbus storm cloud. At full development they can attain a height of 60,000 ft.
Now you may be forgiven for thinking that clouds are just clouds and are just randomly scattered about the sky. Clouds are the result of variations in the air itself; of humidity, temperatures and air currents, but also highly influenced by the sea or land beneath them. They have form and location that are dependent on such things as the topography and temperature of the landmass or the temperature of the sea. They consequently have some predictable and recognisable features. There is a line of clouds off the south coast of Timor Leste that is in the same spot almost every day. A giant cumulonimbus storm cloud that sits above Bathurst Island north of Darwin is so consistent that it has a name… Hector! Clouds such as Hector congregate above islands generated by the daytime heat from the land … huge towering clouds that reach fifty to sixty thousand feet into the upper atmosphere. They are visible from huge distances.
Not only are they visible during the day but also they glow internally at night. Ferry pilots use clouds as beacons during the day and night. Strange as it may sound the colour of the clouds also give reliable clues as to whether or not there is land beneath them. And while clouds are often associated with islands, it’s not always the case. We in our little aeroplane and E7 looking at a line of clouds over the distance horizon may be confused as to which ones are over land and which are over the sea. Clouds reflect the surface beneath them. The reflection of the blue lagoon on the clouds above it are unmistakeable, as do clouds above a forested island reflect the green of the trees.
And there is the visual texture of the sea surface itself that gives those that are observant clues to fixed locations. Oceans currents rise from hidden sub sea topography giving constant evidence of the presence of undersea landmarks almost as if they were visible above the surface of the sea. Between Fiji and New Zealand there is an almost continuous deep trench and ocean mountain range. Such sub sea topography may provide more orientation for birds to follow.
Looking at the flight paths that E7 took there is an evident plan that minimizes the risks of getting lost. Pilots flying to small islands used similar techniques… playing the odds. The pilot estimates the time at which he or she is expecting to get there. If the island doesn’t appear as expected rather than keeping going and run out of fuel and perish it is best to turn at right angles to the track and see if the island can be found. But which way does he or she turn? Go the wrong way… perish again! So pilots would deliberately steer off track to one side and if the island didn’t appear they would know which way to turn to look.
By tracking south from Alaska, E7 would come across the wide stretch of islands and reefs of the Hawaiian Archipelago that stretched across her track from Midway Island to Hawaii itself. Picking up the visual cues of the archipelago from a hundred miles or so away, she then turned southeast towards Fiji. Between the Hawaiian Archipelago and Fiji identifiable landmarks in the Central Pacific Basin, the Gilbert and Phoenix Islands become more common. From Fiji south to New Zealand the Tongan and Kermadec Ridges would guide her until sensing the northern tip of New Zealand she would turn towards her final destination. All the time using the ocean swells as her steering guide.
No creature is born with a map hardwired into his or her brain, birds included. Humans have the most advanced brains of any animal and we certainly are totally ignorant of our whereabouts at birth. Nor can we get anything but the most basic navigation information by staring at the sky. But birds with their great visual sense learn to use the visual cues they receive throughout their lives, guided by their own exploration and following others. It is through this learning process that birds gain the knowledge to navigate. Not only for navigation but they learn to use the visual features of their environment to help them maintain a database of food availability, nesting sites and materials and where to find mates. Very much the same as we do.
Additional information on aircraft navigation systems:
Inertial Navigation Systems
Inertial navigation systems were developed before GPS for oceanic navigation. They consist of sets of very sensitive gyroscopes rotating at high rpm. By measuring the precession of the gyros movement can be detected. The pilots enter the exact location of the parking bay at the departure airport and the motion of the aircraft as it flies across the world detected by the gyros is converted into navigation information. This is a dead reckoning procedure so the pilots use radio navigation information to update their positions from time to time and for the approach and landing at the destination. These days’ fibre optic gyros are used instead of traditional gyros as they are lighter, use less power and are more precise.
Global Positioning Systems
Global Positioning System or GPS as it is more widely known, is in concept not much different to the celestial navigation used by Captain Cook. It just uses round position lines instead of angular position lines to fix the position. GPS uses a constellation of satellites and is dependent on very accurate UTC and the ability to measure time in incredibly small increments.
Like everything, both of these navigation systems have their pros and cons. Inertial navigation is a self-contained system. GPS doesn’t have the accuracy and guaranteed availability to be used solely for navigation. GPS, as well as relying on a satellite constellation that can fail, be interfered with or even switched off.
Radio Navigation Systems
Radio navigation uses a number of different types of radio equipment both on the ground and in the air and is still the most common approach and landing navigation aid. Automatic landing systems used at major airports still rely on radio navigation equipment. However, enhanced GPS corrected by a accurate land based survey site will, in the not to distant future, be so accurate that all the jets arriving at an airport runway will be able to do a blind touch down on the runway on the same tyre prints as the other aircraft before it. And with a software program you could set up a automatic blind landing approach in any where in the world.