Flightless birds

As seen earlier in this blog, flight was gained and lost on a number of occasions amongst certain non-avian dinosaurs. The avian dinosaurs are no different, as birds have become flightless many times.

Already by the late Cretaceous, there were various groups of flightless bird, including the marine dwelling hesperorniths and the ground dwelling patagopterygiforms (Buffetaut & Angst, 2013). The ratites also appeared at this time, and throughout their history, ratites have become flightless not just once but numerous times (Harshman et al, 2008).

Figure 1: Garganuavis, a huge patagopterygiform bird from late Cretaceous France. Though it looks a bit like a ratite the wing claws give away its identity as a member of a more primitive group.  Artist: Joschua Knuppe.

Following the Cretaceous-Palaeogene Extinction 65.5 million years ago, there evolved some enormous flightless birds. The gastornids were enormous relatives of ducks who lived in Eurasia and North America around 56-41 million years ago. Once thought to be predators, studies of their bone isotopes and jaw musculature show them to have been large herbivores (Angst et al, 2014). The phorusrhacids, on the other hand, were definitely predatory. Relatives of cranes, they lived in the Americas, Europe, Africa and Antarctica and existed from around 60 million-15,000 years ago (Dyke & Kaiser, 2011).

Figure 2: Some foolish borhyaenids attempt to steal some prey- a small ungulate- from a phorusrhacid. This will probably not end well for them.  Artist: Renata Cunha.

Today flightlessness exists in 18 surviving bird families (Harshman et al, 2008). In some cases, flightless birds took to a more aquatic lifestyle. This was the case with the penguins, who first appeared around 60 million years ago (Ksepka & Clarke, 2010). Penguin wings have become flippers allowing them to "fly" underwater. It is possible future penguins may evolve into fully aquatic animals.

Figure 3: A couple of Gentoo penguins about to go for a swim. Penguins have become superbly adapted to an aquatic lifestyle, with the wings having become flippers.  Photographer: Robert Heil.

Another thing that can lead to flightlessness in birds is living in island habitats. An excellent example of this is New Zealand, which is inhabited by various flightless birds including the kiwi- a ratite, three species of flightless swamp hen, and the kakapo- the world's only flightless parrot (Fitter, 2009).

Figure 4: A kakapo, the world's only species of flightless parrot.  Photographer: Thomas Gibson.

So why did so many birds become flightless? The answer is, surprisingly enough, that birds are just not exceptionally good flyers. Feather wings can be rendered flightless by something as simple as shortening the feathers and, furthermore, as feathers are made of dead tissue the wings are mostly unable to take in sensory information. Additionally, birds can only launch with their hindlimbs and must flap two to three times just to get airborne (Shipman, 1998). No wonder then that many became flightless.

The next post shall introduce the final group of flyers, the bats.

References
Angst, D., Lecuyer, C., Amiot, R., Buffetaut, E., Fourel, F., Martineau, F., Legendre, S., Arbourachid, A. & Herrel, A. (2014). Isotopic and anatomical evidence of an herbivorous diet in the Early Tertiary giant bird Gastornis. Implications for the structure of Palaeocene terrestrial ecosystems. Naturwissenschaften. 101 (4), pp. 313-322.
Buffetaut, E. & Angst, D. (2013). New evidence of a giant bird from the Late Cretaceous of France. Geological Magazine. 150 (1), pp. 173-176.
Dyke, G. & Kaiser, G. (eds.). (2011). Living Dinosaurs: The Evolutionary History of Modern Birds. John Wiley & Sons Ltd: West Sussex.
Fitter, J. (2009). New Zealand Wildlife. Bradt Travel Guides Ltd: England.
Harshman, J., Braun, M. J., Braun, E. L., Huddleston, C. J., Bowie, R. C. K., Chojnowski, J. L., Hackett, S. J., Han, K., Kimball, R. T., Marks, B. D., Miglia, K. J., Moore, W. S., Reddy, S., Sheldon, F. H., Steadman, D. W., Steppan, S. J., Witt, C. C. & Yuri, T. (2008). Phylogenomic Evidence for Multiple Losses of Flight in Ratite Birds. Proceedings of the National Academy of Sciences of the United States of America. 105 (36), pp. 13 462-13 467.
Ksepka, D. T. & Clarke, J. A. (2010). The Basal Penguin (Aves: Sphenisciformes) Perudyptes devriesi and a Phylogenetic Evaluation of the Penguin Fossil Record. Bulletin of the American Museum of Natural History. 337 (337), pp. 1-77.
Shipman, P. (1998). Taking Wing. Touchstone: Rockefeller Center.

Image sources
Figure 1: Accessed May 5, 2015, from http://fc07.deviantart.net/fs70/i/2011/184/b/e/gargantuavis_by_hyrotrioskjan-d3kv3rf.jpg
Figure 2: Accessed May 5, 2015, from http://41.media.tumblr.com/tumblr_mdbbqeRTk21rqeszyo1_1280.png
Figure 3: Accessed May 5, 2015, from http://images.nationalgeographic.com/wpf/media-live/photos/000/247/cache/gentoo-penguins-jumping-in-water_24700_600x450.jpg
Figure 4: Accessed May 5, 2015, from http://kleberly.com/data_images/wallpapers/9/282092-kakapo.jpg