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Jean Jimenez

Jean Jimenez

Magnificent Frigatebird Expert

The Dynamic Soarer

As I sit on the top deck of this ship, sailing across the cold waters of the Galapagos, an ominous t-shaped silhouette is roaming above the puffy cumulus clouds.

Is it a bird? Is it a plane?

Frigatebird soaring above the yacht. Picture taken by Claudia Quihuis.

As this UFO descended I noticed that it was only just a frigatebird gliding through the sky. I continue to visit the top deck of the ship on a regular basis and always observe the frigatebirds gliding with the ship, occasionally swooping in and out of the path of the ship. But one thing struck me as strange. The frigatebirds weren’t flapping their wings. Instead, their wings were stiffly still and straight like that of an airplane.

Curious about frigatebird flight, I researched the term and many headlines popped up. Most of them read Frigatebirds can fly for weeks at a time[2], Frigatebirds fly nonstop for months[3], and Frigatebirds sleep midflight[4]. Reading these headlines and some of these articles made me curious in how frigatebirds are able to fly for such a long period of time.

Earlier, I described the flight of the frigatebird as gliding. The frigatebird doesn’t glide; it soars. More specifically, frigatebirds are a type of bird that flies long distances using a flight model that aerospace engineers call dynamic soaring[5]. The dynamic soaring model of flight requires a low amount of energy. To understand how dynamic soaring works, we must first understand how flight works.

The shape of the wing influences flight. In fact, the wing shape of frigatebirds is similar to that of airplanes and the same physics are applied[6]. The bottom of the wing is flat and the top is curved, causing air to move faster under the wing than above the wing. This causes a low-pressure system which generates the force of lift[7].

In order to obtain lift, air must be moving past the wing at a certain speed. This is where dynamic soaring comes in.

Dynamic soaring offers the benefit of having air flowing fast past the wing, while lowering the energy investment the bird has to make. The physics behind how dynamic soaring works is the same as the physics behind how roller coasters constantly change its type of energy, from kinetic to potential, or vice-versa. Frigatebirds exploit the natural winds of the ocean to achieve lift. By flying into the wind, the birds are elevated up in the sky. Once in the sky, they have no kinetic energy to keep on flying, but being high up gives them a lot of potential energy. As a consequence, they swoop towards the ocean floor, gaining kinetic energy and losing potential energy on the way. At the last second, the bird makes a sharp turn (spending only a little bit of its own energy) into the wind, repeating the process again[8]. This process happens continuously until the frigatebird reaches its destination.

Frigatebirds are an interesting group of birds to study because of this specific behavior. Studying how this behavior developed throughout natural history gives scientists an insight in the evolution of birds. Frigatebirds are members of a group called Suliformes[10]. This group also include the boobies and the cormorants, which don’t have the ability to dynamically soar. Looking at the phylogeny of Suliformes, the frigatebird is an outgroup, meaning that the species came first[11]. This group has large pectoral muscles[12] allowing them to generate more force and fly for longer periods of time. Although they can all fly for long periods of time, the frigatebird is the only member of the Suliformes that is able to dynamically fly.

Frigatebirds have the largest wingspan to weight ratio[13] compared to all the other bird species. This is one synapomorphy, or a trait commonly shared between the 5 different frigatebird species. This adaptation explains why the frigatebird is so successful at flying long distances without expending any energy. There might be a reason why frigate birds have such a large wingspan to weight ratio. Frigatebirds lack waterproof feathers so they cannot dive for food[14]. The frigatebird is also unable to walk on land[15]. Because of these inabilities, the only way a frigatebird can obtain food is by either harassing other birds and stealing it from them or catch fish that are jumping out of the water[16]. Due to this phenomenon, frigatebirds already have a low intake of energy[17]; thus, they cannot spend as much energy flying, which is one of the few things they know how to do. This can be the driving factor as to why frigatebirds evolved the behavior of dynamic soaring. It is relatively their only way to get around without wasting the little energy it already has.

Suliformes aren’t the only group that exhibits the behavior of dynamic soaring. Albatrosses and petrels, which are other types of seabirds, also use dynamic soaring to fly long distances. If these birds are holding their wings out for such a long time, why don’t they get sore? Or should I say, soar? A study conducted in 1982 determined that albatrosses and petrels have an adaptation that allows them to lock their wings in place, not using as much energy[19]. It’s not surprising that they both have the same adaptation. Both petrels and albatrosses belong in a group pf birds called Procellariiformes[20]. This shared morphology between albatrosses and the petrels suggest that both birds are evolutionarily related. Frigatebirds also share this morphology, yet they are not members of the same clade[21], or phylogenetic group. This seems to suggest that this trait that allows birds to dynamically soar evolved independently at least twice. One evolution occurred in the monophyletic group of albatrosses and petrels. The other event of evolution occurred in the monophyletic group of all 5 of the frigatebird species.

Having evidence that these traits evolved independently shows the important role that dynamic soaring plays in the life of seabirds. Traits that evolve independently usually play a very important role in survival. An example of a trait that evolved independently are eyes. The eyes of mammals and of insects are different and evolved at different times, yet they play an important role for survival. All these seabirds use dynamic soaring because they are seabirds. They live in the ocean, where land masses are far away. Seabirds need this behavior to survive. Natural selection may have selected against birds within these species who are unable to dynamically soar. For instance, if an albatross was born without this wing-locking mechanism, he will not be able to dynamically soar. Since he cannot do this, his fitness, or, his ability to survive and reproduce, is low. Albatrosses need dynamic soaring to migrate[22]. An albatross not able to migrate might die because of environmental conditions. For example, a powerful cyclone might go to its home and the albatross remains stranded. The albatross might not also be able to mate. In seabirds, there exists multiple breeding colonies where a lot of birds go to find a mate[23]. These breeding colonies are evenly distributed along different islands and coastal environments. These breeding colonies are like parties for society’s youth. If an albatross is unable to fly to the breeding colony, it does not mate. Since it doesn’t get to mate, its deformed wing morphology is not passed down to other generations. This is the beauty of nature. Natural selection functions like a spell-checking software which automatically corrects misspelled words. It is nature’s way of keeping itself in check.

Flight has always been very liberating. Watching these birds soar through the sky gives you a feeling of freedom. A feeling that you can just fly away from all that is causing problems in your life. The freedom to soar to any destination in the world without worries. Like the albatross, who can majestically circumnavigate the world in just 46 days[24], effortlessly and without flapping its wings. Like a jet, tearing through the rough, stormy winds of the ever-so-vast ocean. Watching them from the top deck of this yacht makes me realize that the beauty of nature never ceases to amaze me.

[1] Frigatebirds soaring above the yacht. Picture taken by Claudia Quihuis.

[2] Joyce, Christopher. "Nonstop Flight: How The Frigatebird Can Soar For Weeks Without Stopping." NPR. NPR, 30 June 2016. Web. 17 Apr. 2017.

[3] Hamers, Laurel. "Frigate Birds Fly Nonstop for Months." Science News. N.p., 30 June 2016. Web. 17 Apr. 2017.

[4] Costandi, Mo. "Frigatebirds Sleep in Mid-flight." The Guardian. Guardian News and Media, 05 Aug. 2016. Web. 17 Apr. 2017.

[5] Denny, Mark. "Dynamic Soaring: Aerodynamics for Albatrosses." European Journal of Physics 30 (2008): 75-84. Web.

[6] Denny, Mark. "Dynamic Soaring: Aerodynamics for Albatrosses." European Journal of Physics 30 (2008): 75-84. Web.

[7] SPEAR, L. B. and AINLEY, D. G. (1997), Flight behaviour of seabirds in relation to wind direction and wing morphology. Ibis, 139: 221–233. doi:10.1111/j.1474-919X.1997.tb04620.x

[8] SPEAR, L. B. and AINLEY, D. G. (1997), Flight behaviour of seabirds in relation to wind direction and wing morphology. Ibis, 139: 221–233. doi:10.1111/j.1474-919X.1997.tb04620.x

[9] A graphical depiction of how dynamic soaring works. Adapted from Sachs G, Traugott J, Nesterova AP, Dell'Omo G, Kümmeth F, Heidrich W, et al. (2012) Flying at No Mechanical Energy Cost: Disclosing the Secret of Wandering Albatrosses. PLoS ONE 7(9): e41449. https://doi.org/10.1371/journal.pone.0041449

[10] Hackett, Shannon J. et al. “A Phylogenomic Study of Birds Reveals Their Evolutionary History.” Science 320.5884 (2008): 1763. Web.

[11]  Smith ND (2010) Phylogenetic Analysis of Pelecaniformes (Aves) Based on Osteological Data: Implications for Waterbird Phylogeny and Fossil Calibration Studies. PLOS ONE 5(10): e13354.

[12] "SEABIRD OSTEOLOGY." Flight Apparatus, Styles and Wings. Shearwater, 2002. Web. 17 Apr. 2017. <http://www.shearwater.nl/index.php?file=kop135.php>.

[13] "Magnificent Frigatebird." , Life History, All About Birds - Cornell Lab of Ornithology. N.p., n.d. Web. 17 Apr. 2017.<https://www.allaboutbirds.org/guide/Magnificent_Frigatebird/lifehistory>.

[14] "Frigatebirds." Bird Family Fregatidae, Seabirds. Beauty of Birds, n.d. Web. 17 Apr. 2017.

[15] "Frigatebirds." Bird Family Fregatidae, Seabirds. Beauty of Birds, n.d. Web. 17 Apr. 2017.

[16] "Frigatebirds." Bird Family Fregatidae, Seabirds. Beauty of Birds, n.d. Web. 17 Apr. 2017.

[17] Weimerskirch, Henri et al. “Frigate Birds Track Atmospheric Conditions over Months-Long Transoceanic Flights.” Science 353.6294 (2016): 74. Web.

[18] Male frigatebird photographed flying over Mosquera Islet. Picture taken by Jean Jimenez.

[19] Pennycuick, C. J. “The Flight of Petrels and Albatrosses (Procellariiformes), Observed in South Georgia and Its Vicinity.” Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences, vol. 300, no. 1098, 1982, pp. 75–106., www.jstor.org/stable/2395926.

[20] Pennycuick, C. J. “The Flight of Petrels and Albatrosses (Procellariiformes), Observed in South Georgia and Its Vicinity.” Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences, vol. 300, no. 1098, 1982, pp. 75–106., www.jstor.org/stable/2395926.

[21] Smith ND (2010) Phylogenetic Analysis of Pelecaniformes (Aves) Based on Osteological Data: Implications for Waterbird Phylogeny and Fossil Calibration Studies. PLOS ONE 5(10): e13354.

[22] Croxall, John P. et al. “Global Circumnavigations: Tracking Year-Round Ranges of Nonbreeding Albatrosses.” Science 307.5707 (2005): 249. Web.

[23] Fisher, Harvey I. “Some Dynamics of a Breeding Colony of Laysan Albatrosses.” The Wilson Bulletin, vol. 88, no. 1, 1976, pp. 121–142., www.jstor.org/stable/4160718.

[24] Sachs G, Traugott J, Nesterova AP, Dell'Omo G, Kümmeth F, Heidrich W, et al. (2012) Flying at No Mechanical Energy Cost: Disclosing the Secret of Wandering Albatrosses. PLoS ONE 7(9): e41449. https://doi.org/10.1371/journal.pone.0041449