A Brief History of Scientific Inquiry into the Homing Problem
“But as to how memory of home can direct innately the journeys of animals, we have no answer. It is a question with which science has struggled manfully. It is a question as profound as any which biology faces today, for within its unknown answer must lie qualities and properties and potentialities of which we have no least knowledge.”
– Robert Ardrey – The Territorial Imperative (1966)
Why Birds?
After half a year of being too busy/uninspired to post anything I finally found the time and motivation.
I was flipping through a Scientific American article that covered recent insights into how bird biology uses quantum behavior to see the earth’s magnetic fields and couldn’t help but ask, “Just how much effort has gone into trying to figure this out, exactly?” Brief investigation quickly answered, “A lot. Quite a lot.”
A very modest amount of digging gave me a reminder that while new scientific discoveries are fascinating and exciting, they’re built on a body of hard work and previous insights. Not only are these advances made with the wealth from inheritance of older research, but for every breakthrough discovery, there’s also a litany of poorly crafted experiments with confounding variables and questionable conclusions to go along with them.
So, in light of this interesting discovery, I’d like to take a moment to commemorate the fact that the scientific process is an iterative one with ups and downs, shifting paradigms and even potentially conflicting results, but in the end is still a process that brings a greater understanding of the world around us. The road to discovery is a fascinating (and sometimes entertaining) one, built atop a subgrade of curious minds and a base of hard work and careful inquiry.
Some Studies on Birds and Navigation
This is by no means a comprehensive list, but I think it should be a fairly representative sample of experiments that were made over the decades, along with the conclusions that were drawn by the researchers that performed them
(1951) G.V.T. Matthews and the “Untrained” Pigeons
Context
- When people race homing pigeons, the pigeons are often “trained” for the course by displacing the pigeons from their loft in incremental distances, farther and farther away, always in the direction of the prospective race. The assumption was, that a trained pigeon would learn how to get home from the racing point and fly back to the coop faster.
- Mr. Matthews couldn’t help but wonder what would happen with untrained pigeons.
The Hypothesis
- Birds navigate how to get home by learning, so birds that have been “trained” for a race should be quicker to return home than those which are “untrained”.
The Experiment
Matthews observed the behavior of “trained” and “untrained” birds by releasing them away from their roosts and quantitatively measuring:
- Angle of deviation from the desired course
- Speed of setting a navigational direction
- Time taken for a bird to fly from its release point to the vanishing point in the direction of home
The Results
In each category, “untrained” birds actually performed better than the “trained” birds.
The Conclusion
Navigational capacity appears innate in birds and pigeons are possibly confused by the experience of training.
(1951) Gustav Kramer and the Escaping Starlings
Context
- At a station in the East Baltic coast, Gustav Kramer noticed that in October all starlings attempted to escape their aviary to the southwest to begin their seasonal migration.
- He was curious how birds determined this direction.
The Hypothesis
Birds must be able to determine direction by looking at the horizon.
The Experiment
Kramer constructed a round aviary without any discernible view of the horizon or landmarks and observed bird behavior.
The Results
Even without a view of the horizon, the starlings still attempted to escape in the southwest direction.
The Conclusion
View of the horizon is not necessary for birds to determine direction for migration
(1951) G.V.T Matthews and the Magnet-Laden Pigeons
Context
With the results of his previous experiment, and awareness of Kramer’s work, Matthews continued to investigate possible answers to how birds navigate.
The Hypothesis
If birds are able to determine direction without learning or view of the horizon, perhaps they are somehow susceptible to magnetic fields and use the fields to determine direction.
The Experiment
Matthews attached small but strong magnets to the feet of birds to one group, and a similarly weighted brass ballast to the feet of a control group. Birds were then released and allowed to return home.
The Results
All birds returned home with similar outcomes.
The Conclusion
Birds are not dependent on magnetism for navigation.
(1953?) G.V.T. Matthews and the “Cement Mixer”
Context
With learning, the horizon, and magnetism seeming like unlikely answers to the question of how birds navigate, Matthews wondered if birds were perhaps able to determine where they had been taken by sense of memory.
The Hypothesis
- If pigeons are unaffected by magnetism or the horizon, perhaps pigeons have an exceptional “memory” for direction and are able to remember orientation with high accuracy.
- Pigeons that have been disoriented so that they are unable to determine where they are going should not be able to remember the direction of home at all.
The Experiment
- Matthews made an enclosed device that rotated four times a minute and put pigeons in it so they’d flip over (lol).
- The device was placed in his truck and the birds were driven 75 miles away from their roost and let free.
The Results
All birds promptly flew home.
The Conclusion
Birds do not navigate purely by remembering direction of travel in which they have already been taken.
(1955) Pratt, Thouless and the Sun Hypothesis
Context
- By this time it had been observed that cloudy days were one thing that could trip homing pigeons up in their return home.
- Matthews also had data on this from previous experiments on the time of day and homing in pigeons, but his method of releasing birds at six hour intervals seemed to have no effect on homing behavior.
The Hypothesis
If birds are effected by cloudy weather, perhaps they are able to use the sun to determine direction.
The Experiment
Pigeons were released from 60-100 foot towers. One group were taken to the towers in covered crates so that they would have not been able to see the sun until the moment of release. The control group had vision the entire time.
The Results
Birds which had been covered before release took on average ten seconds longer to determine course than those which had not.
The Conclusion
Birds must be partially dependent on the sun for navigation. If this is possible however, this would mean that birds must have an internal clock which is accurate to plus/minus two minutes in the average day.
Contemporary Dissenters
- Gustav Kramer noted that barred warblers only migrate at night.
- R. Drost also noted that the island of Helgoland is often navigated to by birds on moonless nights without difficulty.
(1957) F. and E. Saur Look to the Stars
Context
While the existence of nocturnally migrating birds threw a bit of a wrench into the gears of the sun hypotheses, it was observed that cloud cover also hindered night-flying birds ability to navigate. Perhaps birds use the stars to find their ways home.
The Hypothesis
If birds use the stars to navigate, then removing their ability to see stars should confuse their homing abilities.
The Experiment
- Birds of various species were caged and taken to Zeiss planetarium.
- Birds were then observed during “migration unrest” under a variety of circumstances.
The Results
Birds were able to determine direction under clear and cloudy skies, as well as under projections of stars, but not when the stars were blocked out.
The Conclusion
Birds use stars to some degree when navigating, possibly due to some genetic encoding.
(1962) Barlow and Inertial Navigation
Confession
- So this wasn’t actually an experiment… And the idea didn’t initially start with Barlow… But despite this, it’s still very, very interesting.
- Dr. Barlow can quite effortlessly be described as a very smart man. He is a neurophysiologist at Harvard Medical School who has written books on, among other things, electroencephalograms and how humans perceive time.
- One of Barlow’s papers is a fairly persuasive argument for and explanation of how birds might use inertial navigation. In the contemporary window of advancements with manmade inertial navigation systems for rockets, and planes, and submarines, this was an exciting parallel to draw.
- Also, this paper is highly information-dense so rather than attempt to distill it I’ll just link it for your enjoyment.
(1972) Walcott, Schmidt-Koenig and the Drugged Pigeons
Context
While the paper was released in 1972, Mr. Klaus Schmidt-Koenig had been drugging pigeons since 1960 since that was probably what all the cool scientists were doing at the time. Charles Walcott, while a bit behind the times had developed a similar idea across the pond and the two experiments were eventually submitted in one paper on the behavior of pigeons who have been walloped with lots of anesthetics.
The Hypotheses
Drugs, lmao.
The Experiments
- Schmidt-Koenig: Birds with dosed with Nembutol (a barbituate) and transported to a shelter. The birds were then dosed again at the shelter, and then released later in the day.
- Walcott: Pigeons with dosed with Equithesin, which as the name might imply to some, is an anesthetic for horses. Pigeons were sufficiently zonked out for two hours (as evidenced by literally not blinking with their nictating membranes), and then placed in a sealed container with a freaking Hemholtz coil around it to produce disruptive magnetic fields (lol). After some alien-abduction level shenanigans, the dosed pigeons were released along with a sober (and likely very worried) control group.
The Results
The results in the paper are kind of complicated since but they led to…
The Conclusion
Neither the accuracy of the initial orientation nor the overall homing speed of pigeons was significantly affected by any aspect of the experimental treatment.
(1976) V. Fiaschi and G. Wagner and the Vasoline
Context/Hypothesis
In the early 70’s, Italian researchers postulated that birds could determine their location and navigate via olfactory cues.
The Experiment
In perhaps an overly complicated experiment, some pigeons had their beaks covered in Vaseline, others in a mixture of Vaseline and pinene, and a third group had the olfactory nerve severed the previous year. These different groups were then tested against one another by releasing them in various locations with the pure Vaseline beaked birds considered the control group.
The Results
Olfactory function did appear to affect the pigeons’ ability to find their bearings, with the anosmic group in particular initially placing their bearings at random before flying home.
The Conclusion
This evidence supports the hypothesis that homing pigeons use olfactory cues for navigational purposes.
(1978) Walcott, Schmidt-Koenig and the Frosted Lenses
Context
In an apparently ongoing effort to be the coolest scientists of all time, Walcott and Schmidt-Koening had little plastic glasses and frosted sunglasses manufactured for pigeons.
The Hypothesis
If birds are wearing sick shades that prevent them from identifying landmarks, their navigational abilities will be impeded.
The Experiment
74 plastic-lense pigeons were released in various locations to observe homing behavior, with 18 of the sick-ass frosted lense-wearing pigeons being tracked.
The Results
Frankly, I read this paper and the results are kind of hilarious, but in short:
- Of the 74 pigeons released, 19 managed to return to the loft, 18 stopped en route and were retrieved while 37 were lost.
The Conclusion
From the paper, I’m not sure I would have made this assessment, but as per the last line in their paper, the conclusion is, “The navigational mechanism still remains as obscure as ever, but it is now clear that whatever it may be, it does not require visual information.”
(1978) Kreithen, Quine, and the Isolation Chambers of Pigeon Secrets
The Hypothesis
If birds use infrasound cues to navigate, then they must have high sensitivity to very low Hz sounds.
The Experiment
Birds were “classically conditioned” with electrical shocks to respond to certain stimuli and then placed in isolation chambers with select volumes and ranges of sounds fed in to determine the decibel threshold and wavelength ranges of bird hearing.
The Results
Homing pigeons could detect extremely low frequency sounds (infrasounds) as low as 0.05
Hz in a sound isolation chamber. Classically conditioned heart rate changes were used as a behavioral
measure of sensitivity. Below 10 Hz, the pigeons are at least 50 dB more sensitive than humans.
Conclusions
Birds have sensitive hearing ¯\_(ツ)_/¯
(1984) Lednor, Walcott, and A Study on Gravity (But With Results on Magnets)
Context
Previous studies from Larkin and Keaton found a correlation between birds’ mean vanishing bearings and the day of the lunar synodic month, that is, the birds’ bearings were deflected as a function of the lunar cycle. Several other studies demonstrating changes in bird homing behavior at magnetic anomalies could imply that gravity anomalies could also affect homing behaviors.
The Hypothesis
If birds are released in of gravitationally anomalous locations, this should adversely affect bird homing
The Experiment
An experimental group was released over naturally occurring salt mines with detected gravitationally anomalous readings in Texas, and a control group was released elsewhere in an unfamiliar environment under sunny skies.
The Results
There were no discernible differences in outcome between experimental and control groups.
The Conclusion
Birds do not take gravitational cues in navigating.
capabilities.
(1985) Benvenuti, WallRaff: Olfaction Part II: Smellectric Boogaloo
Confession
This is by no means anywhere near the second experiment done on examining the relationship between smell and navigation in pigeons, but think of the memes.
The Experiment
This one’s a bit wordy so I’m going to cite the summary:
10 experiments were conducted in which a group of experimental pigeons were allowed to smell natural ambient air for a period of 3 h [sic] at a site which was 25-55 km away from the loft (‘ false site’) and then subsequently released at another site (‘ true release site’) situated in a roughly
diametrical position from home. Controls were directly transported to the true release site, and during the same 3 h period they were allowed to smell natural air there. Except for those 3 h, both controls and experimentals were prevented from smelling atmospheric odours by filtration of the air flowing through the containers in which the birds were held. Air filtration was never interrupted in a third group of birds, which were transported together with the experimentals. All the birds were
released under local anaesthesia of their olfactory mucosae. Experiments were performed in pairs: Within each pair of experiments, the site used as ‘false site’ in the first experiment was the ‘true release site’ in the second and vice versa.
The Results
Pigeons that had been given “false” smells flew in the wrong direction.
The Conclusion
Pigeons collect olfactory data whenever it is available, and this informs decisions for navigating home.
(1990) The Beginning of the Bird Science Dark Ages
This is a joke. I just didn’t find any particular interesting studies from this era. Have a link to Even Flow.
(2022) The Article that Started Me Down this Rabbit-Hole
So Why Didn’t we Think of Magnetism in Bird Eyes to Begin With?
Well… We had. Since the 70’s. The problem was that we hadn’t found a satisfactory mechanism for how any kind of electrical “excitement” in the eye could occur to make viewing magnetic fields possible. As summarized in this 1977 paper, we simply hadn’t found a way to explain that behavior yet.
Conclusion
After decades of parallel and competitive research, it would appear that science has a pretty robust understanding of how birds navigate.
I realize I didn’t actually cover this, so in case you want a “quick” rundown of what that scientific understanding is, I’d recommend this website, which even recaps some of the experiments I went over here.
The Oh So Human Beauty of Scientific Inquiry
As with many interesting questions, the answer to how birds navigate is about as far from simple as can be, and it has taken decades of hard work and testing from intelligent people all over the planet for us to even get close to figuring it out.
- These intelligent people designed flawed experiments, operated with insufficient data, and even quarreled among themselves at times. Frankly, with the formidable power of hindsight, I might be tempted to go as far as to say that a number of these experiments were downright goofy (hyuck).
- Despite all of the experimental and human flaws, though, as these men and women operated with a real regard for the process of testing falsifiable hypotheses against reproducible circumstances, they were able to develop humanity’s collective understanding and knowledge in a deep and meaningful way.
- Even today, while the details in the picture of how birds navigate aren’t quite all penciled in, we are still one step closer to really understanding how birds find their way home, and in turn, one step closer to understanding a small piece of this great big world around us.
I sincerely hope that you enjoyed this write-up; I know that I had a blast meandering through history putting it together.
With love,
– Welltree