Re: [TowerTalk] dead birds

[VR2BrettGraham <vr2bg@harts.org.hk>]

N2EA suggested:

> Without a doubt, "communications towers"  didn't
> kill any birds.  It was the flux density of the
> transmitters...and therefore possibly microwave energy,
> or something close to it.

After having watched birds fly very close (as in tens of cm) across the
opening of the feedhorns of the uplink antennas where I work
(with as many as ten HPAs pouring 200-odd watts per carrier into
the feedhorn) & then continue on, or even perch in other well illuminated
areas of the reflector, I'm not so sure about RF being the mechanism.

I don't think you'd find that much power at that sort of frequency on
a tower - especially a big one - in NA, but you guys do have some
serious UHF TV transmitter sites, where the lower frequency is more
than made up for by much more power & the same sort of proximity
is possible.

Don't recall seeing any dead birds at the foot of a tower or along guy runs
on any of the towers I've worked on back there, but out here I have
seen literally hundreds of gargantuan beetles & other "bugs that time
forgot" scattered on the ground at the base of a 120m commercial
tower that an acquaintance has put up at his holiday home up in the
hills of 9M6.

Not much more than low & high-band VHF & perhaps some UHF two-way
stuff on that tower - nothing really significant radiation-wise, if I recall
correctly.  I would think the lights help attract stuff to the towers & then
in the case of birds, differences in towers compared to trees catches them
out (like guys).  Birds attracted to the bugs suggests birds may hang out
near the tower longer, which increases chances of running into a guy (or
greater radiation exposure, I must admit).  In the case of the bugs in 9M6,
it might be that the "attraction" of the tower over surrounding trees means
more going for the tower & therefore the possibility of seeing more of those
that die as there simply as a result of the higher bug density.

Otherwise, what I've seen is that typical amateur antennas & towers tend
to attract birds, who appear to be the better for the presence of the tower.
I have only some dipoles up at the moment, but from the amount of seeds
& droppings I clean up off the roof, I'm getting more birds here than I did
with all the attractive perches the quad provided to them when I lived out
in the jungle.  The experience of others mentioned on this list also tend to
suggest it's very likely that this isn't an issue of concern to amateurs  - 
other
than the possible inclusion of amateurs to anything that might be done to
the commercials.

73, VR2BrettGraham

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