Hi Guys and girls
We had this discussion a few years ago. If you have the time to read it ,here is the concensus;
Dear All, The story from Len Jellicoe about the effect of flash on a
Barn Owl brought some very interesting responses from scientists around
the Neotropics. I'm sure you'll find these as interesting as I did.
Cheers, Robin
>
> There was recently a story of an owl in an area where everyone had
> access to it. As a result, there were many pictures taken with a
> flash. A few weeks later the owl was found dead. Examination revealed
> it had starved to death and that it was blind. I don't know if this
> story is urban myth or is true but it begs the question "is it
> possible" It seems to me that an owl which has many more light
> receptors than a human, may be affected by these flashes as much as a
> human would be affected by a welders flash. I have used flashes on
> birds also, but after hearing this story I now try to get better
> lighting. Any comments on this? Has anyone else heard this story?
> Len Jellicoe
> Surrey, BC
> Canada
>
>
>
> Date: Fri, 27 Feb 2004 07:56:42 -0500
> From: Ellen Paul <ellen.paul@...>
> Subject: Using flash!
>
> Isn't it more likely that the owl was already blind, and therefore did
> not turn away from the flashes or leave the area?
>
> Can a blind owl hunt? Hearing plays an important role in locating prey,
> but nocturnal owls also have good night vision and presumably need
> sight
> to navigate in flight and/or to actually catch prey.
>
> So if the owl was already blind, and if blindness or near blindness
> precludes hunting, that would explain why the owl didn't leave the area
> and why it starved to death.
>
> Question: unless there was visible damage to the owl's eyes, how could
> anyone know if it was blind?
>
> Ellen
>
> --
> PLEASE NOTE NEW EMAIL ADDRESS
> ellen.paul@...
>
> Ellen Paul
> Executive Director
> The Ornithological Council
> Mailto:ellen.paul@...
> Ornithological Council Website:
www.nmnh.si.edu/BIRDNET> "Providing Scientific Information about Birds"
>
>
>
> ------------------------------
>
> Date: Fri, 27 Feb 2004 09:42:43 -0500
> From: "Jack C. Eitniear" <CSTBINC1@...>
> Subject: Re: owls/buhos
>
> It is actually not uncommon for owls to get cataracts. NPR had a story
> about an owl that had cataracts repaired by cornea replacement. Years
> ago I worked at WK Kellogg Biological Station and Bird Sanctuary and
> recall getting a number of such owls in especially during the winter.
> Vision precludes their ability to hunt and they starve unless they end
> up in the hands of a rehab facility.
> Jack Eitniear
>
> Date: Fri, 27 Feb 2004 09:56:52 -0500
> From: Ellen Paul <ellen.paul@...>
> Subject: Owls and flashbulbs
>
> This is a multi-part message in MIME format.
> --------------080903010206000901010108
> Content-Type: text/plain; charset=us-ascii; format=flowed
> Content-Transfer-Encoding: 7bit
>
> Here's a bit I found with google (this is WHY the two guys who invented
> google are now billionaires):
>
> 3. One Hour of Blindness: Retinal rods take 30-40 min to dark adapt
> (i.e. achieve their maximal sensitivity so they can detect single
> photons) after being exposed to bright light. This is true for
> both birds and mammals. A nocturnally-hunting bird would
> therefore
> be out of action in dim light for around 1 hour after being
> exposed to the spotlight. If that hour were crucial for survival,
> or if another team came later and compounded the problem, then
> spotlighting would have deleterious effects that night.[I tried
> to
> capture my letter-wings after they had finished hunting (a
> relatively easy task with this bird because it hunts with the
> moon) and this helped to minimise the impact of spotlighting on
> birds that were feeding young. The impact of being effectively
> blinded for an hour after being spotlighted would have to be
> judged carefully for each bird, based upon knowledge of their
> natural history and routines. Another indirect way that the blind
> period after spotlighting might compromise the subject is via an
> effect on susceptibility to predation. I would not be surprised
> to
> learn that predation risk was increased during this blind period.
> To keep this risk in perspective, however, note that the more
> important senses for evading predators are the mechanical senses,
> like vibration sensitivity, touch and hearing. These have much
> shorter reaction times than vision, which is sluggish to the
> extreme in dim light and may not be missed as much as one might
> think in the area of predator avoidance.
>
> JD Pettigrew FRS
> Professor of Physiology and Director VTHRC
> Vision Touch and Hearing Research Centre
> Ritchie Research Labs, Research Rd
> University of Queensland 4072
> Australia"
>
>
> and from Graham Martin:
>
> "Dr. Graham Martin has been described as "the world's leading authority
> on nocturnal birds and one of the world's foremost vision researchers".
>
> From Dr. Martin
>
> I have dabbled with owls in the past, especially their vision. I have
> often been asked about the truth of similar statements as regards owls
> and other nocturnally active bird species such as shorebirds and
> wildfowl.
>
> In the latter, bright lights are sometimes used in the process of
> "lamping" to catch birds at night. In this a powerful beam is scanned
> around a field until a foraging bird is spotted and then the bird held
> in the beam while it is approached and a net dropped over it. In these
> birds the bright lamp clearly disrupts their behaviour, presumably
> because these birds are fully dark adapted and sensitivity is
> dramatically lost when the bright light is shone into the eyes.
>
> However, this may not be the situation which the photographers are
> arguing about. Some species of owl will actually exploit artifical
> light
> for hunting at night and it is possible for filming purposes to train
> an
> owl to hunt for prey in a pool of light at night. Thus it is not the
> light per se but the disruption of dark adaptation which is the
> essential problem. Whether flash will disrupt dark adaptation
> sufficiently to influence on-going behaviour will depend upon flash
> duration and brightness, and the state of dark adaptation of the
> retina.
>
> Certainly birds do respond to flash. I have used the single flash from
> a
> flash gun to move shorebirds towards mist nets at night, the flash
> causes sufficient alarm to cause a foraging flock to take off and fly
> into the nets.
>
> I have flash photographed captive owls and they seem to be undisturbed,
> but they will even stare straight into a photoflood light, which must
> erradicate any dark adaptation and leave them functionally blind for a
> couple of minutes. Therefore this is not a good indication of whether
> photographic lights will disrupt natural behaviours.
>
> In view of all this, it seems reasonable always to err on the side of
> caution in these matters. The scotopic spectral sensitivity and rate of
> dark adaptation of avian retinas are very similar to those of mammals,
> including ourselves. Thus if our own dark adapted vision is disrupted
> by
> the flash used then it is wise to presume that the bird's dark
> adaptation will be equally affected. If we are temporally "blinded" by
> the flash then so also will be the bird for a similar length of time.
> For example, if you knock out a fully dark adapted retina assume it
> will
> take up to 30min for full sensitivity to be recovered.
>
> Remember also that disruption of dark adaptation is never likely to
> occur in nature. Ambient light levels change through dusk and dawn at a
> relatively slow rate. Even at the equator, where dusk light levels
> change most rapidly, the rate of change is more or less in step with
> the
> rate of dark adaptation, and so under natural conditions a bird will
> always be well adapted to the ambient. With the exception of entry from
> a dark roosting site into full day light, there are few, if any,
> natural
> situations where marked light level changes are experienced and hence
> dark adaptation disrupted.
>
> Obviously during day-time when the retina is light adapted a brief
> photoflash may not even disrupt the state of retinal adaptation.
>
> I hope this furthers the debate.
>
> _________________________________________________
> Graham R. Martin BSc, PhD, DSc.
> (Reader in Avian Sensory Science)
> (Head of School)
> Address:
> School of Continuing Studies
> The University of Birmingham
> Edgbaston
> Birmingham B15 2TT, UK."
>
>
> Date: Fri, 27 Feb 2004 10:26:47 EST
> From: MandRHonigLists@...
> Subject: Re: Owls and flashbulbs
>
> -------------------------------1077895607
> Content-Type: text/plain; charset="US-ASCII"
> Content-Transfer-Encoding: 7bit
>
> I am assuming that the material in Ellen's posting is for white
> spotlights.
> Can anyone comment on whether red lights have the same negative
> effect, or to
> the same degree? I have heard from quite a few people that using red
> lights
> to observe wildlife at night is far less disruptive to the sight of
> the animals
> being observed. From my own experience, I use a small red LED
> flashlight a
> fair amount just for general use (i.e., not wildlife watching), and it
> seems
> that my eyes readjust to darkness far, far faster than when I use a
> white
> flashlight -- also, because there is less glare with the red light and
> thus more
> contrast, it seems that that I see things better with the red light,
> for the most
> part.
>
> Ellen--
> Can you supply the URLs for the web pages from your last posting?
> That's
> real interesting stuff, and I'd like to pass it on to others, but only
> with a
> source indicated. Thanks.
>
> Bob Honig
> Houston, TX
>>
>> Ellen--
>> Can you supply the URLs for the web pages from your last posting?
>> That's real interesting stuff, and I'd like to pass it on to others,
>> but only with a source indicated. Thanks.
>>
>> Bob Honig
>> Houston, TX
>>
>
>
> -
>
> ------------------------------
>
> Date: Fri, 27 Feb 2004 11:16:49 EST
> From: JVMNATREC@...
> Subject: Re: Owls and flashbulbs
>
> --part1_124.2b76e8de.2d70c771_boundary
> Content-Type: text/plain; charset="US-ASCII"
> Content-Transfer-Encoding: 7bit
>
> In a message dated 2/27/04 6:57:39 AM Pacific Standard Time,
> ellen.paul@... writes:
>
>> Remember also that disruption of dark adaptation is never likely to
>> occur
>> in nature. Ambient light levels change through dusk and dawn at a
>> relatively
>> slow rate. Even at the equator, where dusk light levels change most
>> rapidly,
>> the rate of change is more or less in step with the rate of dark
>> adaptation,
>> and so under natural conditions a bird will always be well adapted to
>> the
>> ambient. With the exception of entry from a dark roosting site into
>> full day
>> light, there are few, if any, natural situations where marked light
>> level changes
>> are experienced and hence dark adaptation disrupted
>
> Humm. What about lightning flashes that are quite common in the
> tropics???
> John V. Moore Nature Recordings
>
> ------------------------------
>
> Date: Fri, 27 Feb 2004 13:45:34 -0300
> From: Jim <jjroper@...>
> Subject: Re: Using flash!
>
> We could be confusing cause and effect here. That is, the owl
> was blind or old or feeble originally, which was why it was so
> easy to photograph...
>
> Cheers,
>
> Jim
> ------------------------------
>
> Date: Fri, 27 Feb 2004 12:32:44 -0800
> From: Larry McQueen <larmcqueen@...>
> Subject: Re: Using flash!
>
> This is all very interesting. It's my experience, however, that owls
> observed with white flash lights continue to behave normally and are
> even
> able to catch released mice, fly to their young and feed them. Pupil
> reflex
> in owls is instantaneous under all kinds of conditions. It's
> difficult for
> me to believe a strobe flash would cause blindness, as there had been
> numerous photographers using strobe repeatedly at nest sites with no
> apparent long term or short term negativity on the owls.
>
> Larry McQueen
>
