Re: Tail feathers

["Matthew Troutman" <m_troutman@hotmail.com>]

>1), is looseing the tail feathers a defensive move?

It was probably molting at the time and the feathers were ready to fall 
out. 

>2). Are tail feathers really needed to fly? I know birds do use them to
>break and manevor, but just to fly around, is it really needed? The
>reason I ask is because of Pterodactyloid pterosaurs don't have tails,
>and I've often wondered how they would manever with out them. 

Gatesy and Dial* have done lots of work on this issue.  Basically in a 
bird's body there are three locomotor modules (locomotor 
module="anatomical subregions of the musculoskeletal system that are 
highly integrated and act as functional units during locomotion" Gatesy 
and Middleton 1997;308), pectoral, caudal, and hind limb.  Gatesy and 
Dial have shown that the tail functions as a locomotor module during 
flight.  It has several motions that are unique to each part of flight,.  
During takeoff the tail takes a concave shape and after the first stroke 
the tail moves downward, tucks up, and flares the remiges so the tail is 
near vertical.  When the bird gets off the ground, the tail stays wide 
and low, though flaring is kept to a minimum except during the 
downstroke.  During slow, level flight the tail is oriented horizontally 
and the tail muscles do nothing except on burst of activity during the 
downstroke.  During landing the tail flares downward to slow the bird.  
No tests have been done on unsteady flight, but it is guessed that the 
muscles would be active and the a great help.  Gatesy and Dial also 
produce a cladogram based on their observations (and they show 
dromaeosaurs with one locomotor module, they really have two).  

Based on what it is known about bird flight and the known and 
hypothetical use of the tail during flight, I find it rather perplexing 
that pterodactyloid pterosaurs didn't have a similiar system.  Dave 
Peters has suggested that some of the pterosaur fossils show a 
uropatagium, this could have functioned like a locomotor module.  

I do know for sure that birds that fly like swallows and swifts use 
their tail actively during flight because I have seen it move myself. 

*Gatesy, S.M. and K.P. Dial. 1996.  Lcomotor modules and the evolution 
of avian flight.  Evolution 50: 331-340. 

Matt Troutman


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