Can Blind Birds Navigate? – Monthly Mailbag #8


Hello! Have you ever wondered, do blind birds
can navigate? Welcome to monthly mailbag, where we answer science questions
from the comments section. Seris Efthimiadis asked this one after watching
Jim Al-Khalili’s Discourse on quantum biology. It’s a fantastic question and I’m not
sure there really is a definitive answer to, but let’s dive in and see if we can peck
away at an answer. We all know birds are amazing navigators.
Think of the massive migrations of Canadian Geese, thousands of kilometres every year
across North America. Or the homing ability of pigeons. In fact pigeons are probably the best studied
and most impressive navigators, so lets focus on them for today. Pigeons can find their way back across hundreds
of kilometres of totally unfamiliar territory. How do they do it? It turns out to be pretty complicated and
scientists think pigeons use a whole toolbox of senses and strategies, many, but not all,
of which do rely on functional eyes. But first, to understand what’s going on, let’s break
down navigation: There are two key parts of navigation: determining
where you are in space, a map, and which determining direction is which, a compass. You then need to constantly update those two
things to make sure you are where you think you are and you’re going where you think
you’re going. So let’s imagine dropping a bird off at
the Eiffel Tower in Paris, 342km from the Ri in London. How will it get home? Our bird’s never been to Paris, so there’s
no chance of it navigating just by visual landmarks it might recognise. Which is what
we think pigeons usually do. So how is it going to get home? First, the compass we talked about. Birds
use two major sources of information: the position of the sun and the stars in the sky,
and magnetoreceptors in their eyes. Both of these mechanisms depend on working eyes at
least to some extent, so it’s not looking very good for Seris’ blind birds. The sun can act as a compass for pigeons because
they have a very accurate internal clock, so they can tell which direction is which
based on the position of the sun or the stars in the sky. Scientists have been able to test
this ability by artificially making birds change time zones. They turn lights on in
the middle of the night and they turn them off during the day. Birds that have been time-shifted
like this will get their directions wrong, but not randomly, they’ll get them wrong in
a very predictable way. For example, if home is due west and it is
6pm in their head, then they’ll expect the sun to be, let’s say, 20 degrees above the
Western horizon. So they’ll fly towards it. But if they’ve been time shifted so
that it’s actually 10am and the sun has recently risen, they’ll fly East, in exactly
the wrong direction. But if it’s cloudy, then even time-shifted
birds navigate just fine, so we think the pigeon’s first option is the sun compass,
and then they resort to using their other senses, including magnetoreceptors in their
eyes. Now THIS is cool… There’s a type of protein called cryptochrome
that lives in the retinas of a lot of birds. And it’s reactive to blue light. So what scientists
think happens is that when blue light hits cryptochrome, it becomes “active” and
will remain so for a little while until it deactivates again. The amount of time that
it stays active is affected by the strength of the Earth’s magnetic field. And cryptochrome
is also known to affect the sensitivity of the retina. To see what that might look like
to a bird, let’s go to the roof. So what scientists think happens is that when
a bird looks South, dark patches align over their vision, kind of like this. As they look around, the patches move too,
giving a constant sense of compass direction. We also have cryptochrome in our eyes, but
the molecule that lets it stay active for long enough to be affected by the magnetic
field, superoxide, is toxic, so the antioxidants in our eyes lock it down too quickly. Researchers
think we’ve traded longevity for magnetovision. So our pigeon in Paris is going to be able
to orient itself pretty well, as long as it’s not blind, Seris. It knows where North is,
but how does it know that London is North? How does it build itself a map? It’s still
kind of an open question, but we do have some more clues. It’s either more magnetoreception
or odour maps. Apart from the cryptochrome in their eyes,
pigeons also have magnetite, a biologically formed, iron-rich material that reacts to
magnetic fields, in their heads. Exactly where is still a matter of some debate – it could
be in the skin on the top of their beak, near their nostrils, or between their brain and
their skull. But in any case we’re pretty sure it sends signals to the brain via the
trigeminal nerve, which is the same one that controls the eyes, so if Seris’s blind birds
have nerve damage, this method won’t be of much help. Tiny particles of magnetite get aligned to
the Earth’s magnetic field, just like needles in this demonstration from our museum. The
mini compasses will align to the strong magnetic field imposed by this bar magnet. So imagine
the pigeon’s beak is full of micrometre-sized compasses, each a fraction the width of a
human hair. So that works fine as a compass, but it can
also work as a map. The way they all get aligned will tell the bird where it is on Earth, because
of a concept called a gradient map. The intensity of the Earth’s magnetic field varies with
distance to the poles, being stronger near the poles and weaker near the equator, so
that gives latitude information. But the field also varies in inclination, being vertical
at the poles and horizontal near the equator. And it’s the combination of these two things
where the bird can build a bicoordinate system. Intensity and inclination vary across the
world and there’s a unique set of values for any given point on Earth. The bird builds up a feeling for the magnetic
field at home and how it changes when it moves in various directions. It then extrapolates
that local map out, assuming the pattern will continue to cover the rest of the Earth. It turns out that this magnetite map probably
only works on a very local level, up to 15km or so, or at very large scales, 50km or more,
because in small areas variation caused by the metal content of underlying rocks is too
localised to be extrapolated very far, and in contrast the gradual change in the Earth’s
magnetic field can only be reliably sensed at very long distances. There’s also some suggestion that pigeons
can extrapolate familiar prevailing smells in similar ways, to build up an olfactory
map. But it’s unlikely that this can create the kind of gradient map that could reach
as far as Paris, so it’s probably restricted to creating more of a pungent mosaic of the
bird’s home town. Useful when the journey is nearly over, but not so great for setting
a course 300km away. So to wrap this all together, let’s return
to our brave pigeon’s voyage. He sets off from the Eiffel Tower and starts looping around,
getting his bearings. He quickly realises he doesn’t recognise anything around him
in this strange and foreign land. So he checks the position of the sun against his internal
clock and cross-references that with his perception of the Earth’s magnetic field to calibrate
his compass. He has a sniff but doesn’t recognise the
cheesy smells of France so extrapolates what he knows about the large-scale gradients in
the Earth’s magnetic field to place him on a basic mental map, and sets off roughly
in the right direction. As he crosses the Channel small cues from
his olfactory map confirm he’s heading in the right direction as he catches the unmistakable
pong of England. He speeds up. He hits the Thames and can see the Shard poking up in
the heart of London in the distance. He picks up those familiar tinglings of the local magnetic
field variations, and in no time he’s found his way back to the warm embrace of the Royal
Institution. But he used his vision and his eyes an awful
lot there. So to answer the question once and for all, do blind birds can navigate? No, probably not. Thanks for watching. If you have a science
question that you always wanted answered make sure to pop it in the comments below and if
you enjoy our videos make sure to subscribe for a new one every week.

15 thoughts on “Can Blind Birds Navigate? – Monthly Mailbag #8

  1. We often judge the intelligence of other animals based on well they do on tasks that humans are good at. If pigeons were to give intelligence tests to humans, the pigeons would conclude that humans are complete idiots.

  2. Thank-you, nice talk. Complementary question…..how can the current SPEEDING UP CHANGE in position ( movement) of the true north (or south ) magnetic pole affect (or will it) the migration of birds, especially a single pingeon reaching thru its unknown territory over time ( because the magnetic poles locations are moving faster about each year? See if you can respond that….Tks

  3. Reminds me of Game of Thrones where they send ravens to exact spots (castles) like they're emails ffs lol

  4. This would need some testing / experimentation with mail pigeons. Problem is you need to devise a system where the blinding eye patch for the pigeon would wear off in a day. And you need to give them a gps tracker because you'd probably need to see where they do make it if they get lost and return later because the eye-patch wears off (has she been flying circles for a day near release point, or near destination until eye-patch wears off?). Test some with one blinded eye, some with a small magnet on their head.
    Probably the only way you can test with blinding 2 eyes is if you drop them from a plane. Otherwise they won't fly or just fly into the next tree/building/pole/windmill/electricity cable etc.
    Assuming they would fly and get their bearings and not just drop down and sit there until they can see again this could happen:
    – once they realize they can fly even when blind, without crashing, they'd probably get a rough bearing where to fly to.
    – that will get them to around 50 km/mile near destination
    – if she's never been there either she would probably get relatively lost for a while until she picks up a smell
    – once they get a familiar smell they probably could find the neighborhood within a couple of miles but would be unable to land because of no vision.

    Pigeons in the night I can just pick up, they usually refuse to fly. They can see me coming, they look right at me and try to walk away, but they react slow. When you then throw them in the air they sometimes fly right back to the nearest place they could sit on. Other times they just fly away out of sight and do not return anywhere near until next morning. They won't return to the exact place they were caught in the dark though, because that is forever deemed unsafe (use this if you don't want pigeons on your balcony).

  5. I really like this kind of non offensive yet funny way to pick on people who don't bother to write correctly.

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