10 things we didn’t know about seabirds (until now)
Electronic tracking devices have transformed our insight into the lives of birds at sea. Globe-trotting ornithologist Dr Michael Brooke describes some of the most fascinating seabird discoveries from his new book “Far from Land – The Mysterious Lives of Seabirds”.
Seabirds have always proven elusive subjects to study. They spend much of their lives roving the open ocean, or nesting on remote islands far from human eyes. But thanks to modern innovation, increasingly small and lightweight devices can be attached to a wide range of species, giving us a completely new outlook on their movements and behaviour. Here are just some of the highlights.
1. The Great Frigatebird can fly in its sleep
Great Frigatebirds Fregata mino can remain aloft over open tropical seas for a week or more, gaining height over rising thermals and then slowly descending, before repeating the process.
When their sleep patterns were monitored by an attached electroencephalogram, it was found that Great Frigatebirds go to sleep while aloft - but only for 42 minutes per night, instead of for the 12 hours enjoyed when roosting onshore. Three-quarters of this flying sleep involves just half of the brain at a time. The fact that the remaining quarter involves both brain hemispheres simultaneously shows that going to sleep is not incompatible with controlled flight.
2. The Wandering Albatross spends its first five days at sea swimming
As its name suggests, the Wandering Albatross Diomedea exulans is famed for its marathon flights. But it has to start somewhere. Tracked from Iles Crozet in the Southern Ocean, young Wandering Albatrosses leaving the nest spend the first five days mostly swimming. However, as they acquire flight efficiency, they soon begin to cover 600 km/day and, on average, clock up 184,000 km during the first year at sea: equivalent to four times round the world.
With the help of skeleton features that allow the outstretched wing to be ‘locked’ into position, the heart rate of gliding Wandering Albatrosses (around 80 bpm) is barely faster than the rate of birds resting on the water (around 60 bpm). Thus, vast distances can be covered at very little energetic cost.
3. Thick-billed Murre fathers accompany their fledglings out to sea
When a young Thick-billed Murre Uria lomvia fledges by leaping off the nesting cliff, it is about a third of the size of an adult. On its maiden voyage, it is accompanied out to sea by its father. Tracked south from a west Greenland colony, one father-youngster pairing swam south together for 3,000 km.
Paternal accompaniment of the chick is also the norm in Common Murres Uria aalge and Razorbills Alca torda, and perhaps also occurred in the extinct Great Auk. Just why the male rather than the female should shoulder this task is not known. During the journey, contact is probably maintained by a combination of sight and call. But there must be occasions when the juvenile, encountering a seething maelstrom of salt spray for the first time, is terrified of losing contact with its lifeline, its father.
4. A Whimbrel can fly through the eye of a storm
While migrating south along the eastern seaboard of North America in autumn 2011, a Whimbrel Numenius phaeopus named 'Hope' encountered Tropical Storm Gert off Nova Scotia. Undeterred, she entered the storm at a ground speed of about 12 km/h. Passing the eye, Hope emerged – or was ejected – 27 hours later at a speed of 150 km/h. She immediately changed course and took plan B, an escape route to Cape Cod on the Massachusetts coast.
Modern studies repeatedly demonstrate how seabirds are not tossed hither and thither by the wind. Instead, they can use prevailing weather patterns to their advantage and, when necessary, cope with extreme weather. Even when things go awry, there is potentially a Plan B, as Hope’s change of course illustrates.
5. Northern Gannet feeding grounds barely overlap – even when colonies are right next to each other
Northern Gannet Morus bassanus colonies are dotted around the coasts of Britain and Ireland but, even when the colonies are as close as 30 km from each other, birds from neighbouring colonies use largely separate feeding areas.
Most striking is the pattern off the west of Ireland. There are situated two colonies, Little Skellig (29,700 pairs) and, about 30 km to the south, Bull Rock (3,700 pairs). Little Skellig birds head overwhelmingly northwest, away from neighbouring Bull Rock (and the Irish mainland), while the Bull Rock birds head south. It is possible this pattern arises because birds learn the best feeding areas by following other gannets leaving their colony, and especially by immature gannets following their elders.
6. Paired Sabine's Gulls can re-unite after extreme separation.
One pair of Sabine’s Gulls Xema sabini, nesting together in the Canadian Arctic, spent the northern winter far apart, she over the Humboldt Current off Peru and he over the Benguela Current off South Africa, only to re-unite the following spring back in the north.
Derived from lightweight geolocators attached to the birds’ legs, this extraordinary finding raises fascinating questions about how a young bird’s migratory habits might be inherited from its parents, especially when mother and father go to very different areas outside the breeding season.
7. The Emperor Penguin is the king of deep diving
The Emperor Penguin Aptenodytes forsteri is the champion diver among seabirds. The maximum depth recorded is 564 m and the maximum duration underwater 21.8 minutes.
It is probably no surprise that penguins are the most proficient seabird divers. However, other groups also achieve impressive depths, with guillemots occasionally diving to below 100 m and shearwaters to 70 m.
8. Penguins use expanding air to burst out of the sea
Think of the shame befalling an Emperor Penguin that does not leap high enough when exiting the water. It splatters onto the ice and then back into the sea, where predatory leopard seals lurk. It is therefore very important that the penguin adjusts its exit speed according to the height of the ice cliff. Much of the speed of a penguin exiting the water comes from the expansion of air bubbles trapped within its feathers. As the bird rises to the surface and the water pressure drops, this expansion creates ever-greater buoyancy until eventually the bird pops, cork-like, to the surface. And the greater the depth at which the ascent starts, the greater the exit speed.
9. The Northern Gannet risks wind turbine collisions when hunting
When travelling from A to B, Gannets fly about 11 m above the sea, but ascend to about 26 m when entering searching mode prior to a plunge.
This might seem an esoteric fact – but not so. In UK waters, the minimum permitted height of an offshore wind turbine blade is 22 m. Thus gannets are fairly safe from a blade’s swipe when commuting, but in mortal danger if they begin searching for fish within the perimeter of a windfarm.
10. Murphy’s Petrels go to South America when off-duty from incubating eggs
Murphy’s Petrel Pterodroma ultima parents take it in turn to incubate their eggs in shifts. When off-duty for around 20 days during incubation, a Murphy’s Petrel from the colony on Henderson Island in the South Pacific can complete a 15,000 km loop towards South America, taking it to a maximum distance of 4,500 km from home.
In general seabirds travel further from the colony during incubation than when feeding chicks, simply because commuting time is restricted by the need to visit the chicks fairly frequently.
Murphy’s Petrel are one of the many breeding seabirds set to be protected by BirdLife in a current project on Rapa Iti.
So we can see that modern technology does much more than tell us where seabirds congregate. As useful as this is when working out where to locate Marine Protected Areas, tracking devices can also tell us ways in which a bird’s habits could put it in danger, as well as how best to solve these problems. Aside from all that, shedding light on their unique and captivating behaviours drives home the importance of conserving such wonderful diversity.
Dr. Michael Brooke
21st August 2018