4
$\begingroup$

The boat-tailed grackle's deep-V tail would seem to cause a great deal of drag or even downward deflection (like an airplane's elevators). How much does this actually affect the bird's flight?

Boat tailed grackle

$\endgroup$
  • $\begingroup$ It's considered a requisite on biology.se that at least some reading/research is carried out and presented with your question. [For example, do you have any evidence that boat-tailed grackles fly less efficiently than other birds? What criteria would you use to measure that?] Otherwise it will be closed as homework. The site tour and the help center provide guidance on how to use this site. Please take a few minutes to read about the kind of questions which are on topic here. $\endgroup$ – anongoodnurse Jan 28 '15 at 23:59
  • 1
    $\begingroup$ @anongoodnurse: A Google search for this information turned up no satisfactory information. Now, 50 minutes after posting, this question turns up as the number one result and a duplicate of this very question on a copy-cat site shows up a few entries lower. I have no evidence other than my intuition and curiosity. You can be sure that I'm quite familiar with how StackExchange works. $\endgroup$ – Paused until further notice. Jan 29 '15 at 0:08
  • $\begingroup$ I don't know... perhaps Physics.se would be a better site for your question. Yeah, copying happens. If you think it's iffy, flag a mod with the info. $\endgroup$ – anongoodnurse Jan 29 '15 at 0:22
  • 2
    $\begingroup$ Aside from a detailed study of the flight envelope of many bird species(which might not exist), the answer might have to be 'They're efficient enough, according to the boat-tailed grackle at least'. Lots of birds have ridiculous plumage or other things that impede their flight. See: peacocks, birds of paradise, etc. Birds, weirdly enough, aren't designed to fly very well. Some are designed to look good or hide efficiently or whatever it is birds do. $\endgroup$ – Resonating Jan 29 '15 at 0:25
  • $\begingroup$ @Resonating: Of the birds with unusual plumage shapes that I'm aware of, the only ones I've had the opportunity to observe with any frequency are the grackle which fly a lot and (with much less observation) peacocks which don't seem to fly nearly as much. I don't imagine lyrebirds, for an example which I haven't had the opportunity to observe, fly very well - the same (observation or flight ability) probably goes for many of the birds of paradise that you mentioned. As for a general statement of whether birds are designed to fly very well - I can think of many counter examples. $\endgroup$ – Paused until further notice. Jan 29 '15 at 0:41
7
$\begingroup$

I don't know of studies specifically of boat-tailed grackle flight, so I'll focus on elongated tails in general and come back to grackles at the end.

Long tails in birds are obviously interesting from the standpoint of sexual selection. Going all the way back to Darwin, one hypothesis has been that females prefer males with long tails. There seems to be evidence for this, although experimental reduction or elongation of tail feathers is perhaps of questionable success. See this back and forth in Behavioral Ecology.

Those interested in the study of flight have also studied elongate tail feathers to get at the questions you ask: are long tail feathers aerodynamically costly?

Balmford (1993) compared the aerodynamic properties of different tail shapes. He found that:

A forked tail that has a triangular planform when spread to just over 120° gives the best aerodynamic performance and this may be close to a universal optimum, in terms of aerodynamic efficiency, for a means to control pitch and yaw.

But the results were more complicated. Forked tails are only used in extreme maneuvers, they are more unstable, and suffer from greater loss of performance when damaged. He leaves open the possibility that natural selection, rather than or in addition to sexual selection, has played a role in shaping bird tails, possibly for increased aerodynamic performance.

More relevant here, Balmford et al. (1993) studied pairs of species, one with a long tail and one without, to assess the aerodynamic cost of long tail feathers. They studied ~600 specimens and used aerodynamic modeling to predict cost. Their results are summarized in this figure:

Tail Shape

Graduated (rounded) tails are costliest over all lengths. Forked tails are notably less costly over all lengths, and shallow forks more efficient than deep forks (but there the difference is not great).

They conclude:

Our model suggests that as long forked tails deepen, it becomes more likely that they are aerodynamically costly..., and therefore increasingly probable that sexual rather than natural selection explains their evolution.

And of the species pairs:

... then among species with long forked tails, sexual dimorphism in tail length should increase with fork depth. Pairwise comparisons of closely related species support this prediction.

What of boat-tail grackles then?

From what images I could find, it looks like boat-tailed grackles appear to have graduated tails when spread. If so, then these tails would be very inefficient and males with longer tails would incur a proportionately higher cost of flight than males with shorter tails.

Balmford, A., A. L. R. Thomas, and I. Jones. 1993. Aerodynamics and the evolution of long tails in birds. Nature 361:628–631.

Thomas, A. L. R. 1993. On the Aerodynamics of Birds' Tails. Philosophical Transactions of the Royal Society of London B: Biological Sciences 340:361–380.

$\endgroup$
  • $\begingroup$ Instead of a fork or a simple graduated shape, boat-tailed grackles have a deep V (you might say in the vertical direction as opposed to a fork in the horizontal direction. They don't flatten that V in flight. $\endgroup$ – Paused until further notice. Jan 29 '15 at 15:39

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.