On Fri, Jul 21, 2006 at 04:26:12PM +1000, Philip Veerman wrote:
> Would it be possible for the internal guidance system of a
> Grey-headed Lapwing to sense that it was heading south and
> not north whilst locked in a dark metal can?
Enclosures of most metals don't exclude magnetic fields but magnetic
orientation is light-mediated in birds - so its magnetic compass won't
work in darkness. Birds can separately sense magnetic field intensity
which could provide navigational cues but the can will impair this by
perturbing/attenuating the earth's field - how much depends on which
metal.
There are suggestions birds also get navigational cues from infrasound
(low frequency sound) which might penetrate the can.
Inertial navigation would be unaffected by enclosure in a metal can but
birds are thought not to use it.
There is a nice summary on magnetic navigation in birds here:
http://www.uni-greifswald.de/~zoologie/german/phybioti/wiltschko05.pdf
In another thread John Leonard mentioned that feral cats can be hunted by
running them down as they don't much stamina. Humans can actually outrun
most mammals over long distances - perhaps due to adaption for this type
of hunting. The mammal in the current Australian fauna we definitely
couldn't hunt this way is the camel, a few other like horses might have
a marginal advantage, but most species if we can continue the pursuit,
we'll win.
Some bird definitely exceed our capabilities, long-hop migrants, exercise
continually at high-intensity for 2-3 days and do it fueled almost
entirely from their fat reserves. We can't metabolise fat fast enough to
sustain high intensity exercise. For tour-watchers, even the scrawniest
cyclist of the peleton would have fat reserves suffcient to fuel them
for 1000+km, but during each stage they must take on board considerable
amounts of food - particularly sugars - to sustain the high-intensity
exercise. Not an option for a long-hop migrant in mid-ocean.
Andrew
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