I've been interested in Animal Navigation for years. I've always been interested in things like orientation and maps and so on, but it was when I started working with the Efe Pygmies in the mid 1980s, and noticed that there were some interesting things about how they found their way around in the rainforest, that I started to track and absorb the literature on the issue. Back then, there were a few researchers who felt that some animals, possibly including humans, had built in navigation equipment, possibly using magnetics. Some of those researchers oversimplified their models and took the position that if pigeons could home with a built in compass, than so could humans, for instance. Some of the research was a bit zany and I think the world of zoology was not quite ready for the idea that organisms had built in electronic (magnetic, actually) parts. The physiology of navigation remained controversial for some time, and many of the researchers who had valid findings, it seems needed to be careful how much they pused their ideas.
We've come a long way since then, and a recently published book, Nature's Compass: The Mystery of Animal Navigation
This book covers navigation in a wide range of animals living in a diversity of habitats around the world. Navigation by animals is not simple. Most animals use multiple systems, though one system or another may be primary. Some of the things animals do to navigate can only be thought of as the use of senses other than the ones we usually assume exist. It turns out that humans are nothing special in the area of navigation. Many other creatures have us beat in keeping track of time and space relationships. This is as expected, since primates are rarely migratory and rarely cover large distances. (Humans are unique in this regard, I'm pretty sure.)
The book covers basic problems in navigation, keeping track of time, internal compasses, internal maps, and important issues related to conservation and extinction. Enough of this book addresses birds that I'm listing this review under "bird books" but it is by no means limited to Aves.
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I ran across this interesting reference (reading the What if blog by xkcd author Randall Munroe, of all things):
"Magnetic alignment in grazing and resting cattle and deer"
PNAS 105:13451–13455 (2008)
http://www.pnas.org/content/early/2008/08/22/0803650105
Magnetic sensing seems to be pop up in unexpected places.
A few notes and wild guesses about "senses other than the ones we usually assume exist."
=Magnetic orientation.
=Precise time sense associated with memory for route taken (certain species of ants that live in featureless deserts).
=Electromagnetic interference patterns seen optically (QM effects on magnetic particles in the eyes: certain bird species).
=Low-frequency vibrations picked up through the feet on the ground (elephants, and there is some evidence they use this for communication or at least detection of other elephants nearby).
=Sonar transmission & reception (bats).
=Infrared light (bees).
=Differences in color perception optimized for environments (similar to the way some "color blind" humans can spot subtle differences, such as picking out camouflaged military units in a forest).
=Greater directionality of sound (anecdotal: cats, dogs).
=Ambient static electric potential in the air (hypothetical: sensed as response of fur to static charge).
=Ultraviolet light as tactile sensation (anecdotal: personal experience & experience of friends, "prickly" sensation in the skin under high UV light conditions).
=Variations in sense of time passing, such as "slow time" during chase/evasion maneuvers. ("position in time" or "what time it is," is different to "passage of time" or "how much time has passed since event X")
=Smell and taste sensitivities to compounds or concentrations that humans can't detect (dogs).
The conventional reference to "our five senses" really does us a disservice, because it tends to constrain thinking on this subject. For example what we normally think of as "the sense of touch" includes items such as the vestibular sense (movement through space) and kinaesthetic sense (feedback from voluntary musculature) that should be thought of as distinct.
Excellent list, and there prob. is more. Owls have offset ears and funny neural mechanisms to let them super-accurately localize sounds. Birds can "see" magnetic fields (that's pretty recent research) . The lateral line is a sense organ and provides "lateral line" sense, as it were.
A colleague of mine did research on subsonic sounds and humans. We may emotionally react to distant thunder heard only through our feet, as it were. Maybe.
Thanks Greg.
Re. subsonic sounds & humans: I live near the Hayward Fault, and have heard anecdotal reports that dogs and some other animals apparently react to "something" immediately before earthquakes. I figured it was probably subsonic vibrations that might be picked up through feet on the ground. I trained myself to become alert to such things, and so far have only gotten a bunch of false-positives from items such as trucks going by.
Here's another interesting audio effect & hypothesis for it:
Using a binaural telephone headset (technically it's not really "binaural," it just has earpieces over both ears) on my desk phone makes it easier to understand "cellphone speech." Normally the packetization of cellphone transmission sounds to me like someone talking through spinning fan blades: as if the audio is broken up and stuffed into a stream of envelopes approximately similar to a rectified sine wave at the packetization frequency. This is highly annoying at minimum (and probably not noticed by the majority of people, all they know is they prefer other modes of communication than talking on the phone). But having an earpiece on each ear smooths out the packetization, so cellphone speech "merely" sounds muffled.
My tentative hypothesis for that is: It's not a matter of "two ears are better than one," it's a neural artifact. There's a lag of a few milliseconds for a signal from each ear to pass through the corpus callosum to its destination in the audio processing area in the opposite brain hemisphere. The lag from both ears to their opposite hemispheres just happens to coincide with the packetization frequency in a manner similar to destructive interference: the packet peaks are averaged enough to be much less noticeable.
To test that, transmit both pure analog tones and white noise from a cellphone to a landline desk phone hooked up to an oscilloscope, to try to measure the packetization frequency and the amplitude of the packetization waveform. Next, amplitude-modulate clean white noise in the same manner and present it to one ear only, and then both ears, over headphones. If the modulation was rendered less audible by being heard in both ears, the last step would be: vary the modulation frequency and amplitude to ascertain the limits of the suppression of modulation. Then test on other willing volunteers (I have friends who won't mind guinea-pigging for something like this) to ascertain if the effect works at all for them and if so, what its parameters are for them.
And as a bonus experiment: try feeding volunteers a) unmodulated white noise, b) modulated white noise in one ear only, and c) modulated white noise in both ears, while they attempt to complete concentration tasks. The hypothesis here is that the modulation interferes with concentration tasks, perhaps by entrainment of brain activity (which in turn could be measured on an EEG). If so, this might shed light on "cellphone driving."
Yes, you too can have hours of fun experimenting with your own senses & perceptual artifacts. Who needs video games when you have a brain to play with? ;-)
Interesting. I have the same perception when I hear cell phone talk; I had never put it that way but that is what it sounds like, as if coming through fan blades. I'll have to try that.