Overblog Suivre ce blog
Editer l'article Administration Créer mon blog
15 février 2011 2 15 /02 /février /2011 15:19

For once, there is a good news about ecology. For a while now, falcons are back in Paris!

 

The Peregrine Falcon (faucon pélerin) was an endangered species in many areas due to the use of  organochloride pesticides, especially  DDT (dichlorodiphenyltrichloroethane). Pesticide accumulation caused organochlorine to build up in the falcons' fat tissues, reducing the amount of calcium in their eggshells. With thinner shells, fewer falcon eggs survived to hatching.  Since the ban on DDT from the beginning of the 1970s, the falcon is  reappearing (even in cites) and a couple just settled on the Areva building in the business center La Defence.

 

faucon.jpg

 

faucon2.jpg

 

 

Areva used to shit on Nature, but now the Nature is shitting back on Areva! Sounds fair.

 

The LPO (Ligue pour la Protection des Oiseaux) tried to organized some nesting place on the roof of other building, with no success so far. Indeed, the Falcon nests normally on cliff edges (mountain ranges, river valleys, coastlines) or, more recently, on tall human-made structures, to catch sight of prey using their amazing vision. Indeed, they have two forveas, i.e. the part of the eye located in the center of the retina and responsible for sharp central vision. One of them has five times as many visual cells than ours and is shaped like a telephoto lens, enabling her to see prey as far as 10 kms away.

 

fovea.jpg

                                                 faclon fovea                                       vs                                            human fovea

 

 

It's also the fastest animal on the planet in its hunting dive, the stoop, which involves soaring to a great height and then diving steeply at speeds commonly said to be over 320 km/h (200 mph), and hitting one wing of its prey so as not to harm itself on impact.

 

falcon-curve.jpg

 

 

The mystery of why peregrines approach prey by flying along curved paths that resemble spirals have been solved by Tucker et al. Tests have shown that they see objects in front of them most clearly when they turn their heads about 40 degrees to one side (i.e, the image falls on the deep fovea; see Figures above). But turning their heads in mid-flight might increase the birds' aerodynamic drag, slowing them down. To test this, Tucker placed models of Peregrine Falcons in a wind tunnel. Force sensors showed that, at a wind speed of 42 km per hour, the drag on birds whose heads were turned 40 degrees was more than 50% greater than on those looking straight ahead. To avoid this, Tucker concludes, the birds keep their heads straight and follow a path called a logarithmic spiral. That way, they can keep one eye fixed on their prey. And while a spiral path is longer, the speed advantage more than compensates.

 

 

 

 

 

Welcome back to the "ville des Lumières" Horus!

 


 

horus.jpg

 

Horus' eye: ancient Egyptian symbol of protection from the falcon-headed god Horus.

 

millenium-falcon.gif

 

Of course I cannot talk about falcons without quoting the best starship ever: the millenium falcon.

 

 



THE DEEP FOVEA, SIDEWAYS VISION AND SPIRAL FLIGHT PATHS IN RAPTORS VANCE
A. TUCKER
The Journal of Experimental Biology 203, 3745–3754 (2000)

CURVED FLIGHT PATHS AND SIDEWAYS VISION IN PEREGRINE FALCONS (FALCO PEREGRINUS)
VANCE A. TUCKER, ALICE E. TUCKER, KATHY AKERS AND JAMES H. ENDERSON
The Journal of Experimental Biology 203, 3755–3763 (2000)

GLIDING FLIGHT: DRAG AND TORQUE OF A HAWK AND A FALCON WITH STRAIGHT AND TURNED HEADS, AND A LOWER VALUE FOR THE PARASITE DRAG COEFFICIENT
VANCE A. TUCKER
The Journal of Experimental Biology 203, 3733–3744 (2000)

Partager cet article

Repost 0
Published by doc-fab - dans Sciences
commenter cet article

commentaires