It is the sound which first alerts me to their arrival. The oncoming roar of multitudinous wings – flapping, lifting, banking, braking – is accompanied by a brash cacophony of squeaks, cackles, and chucks arising from hundreds of avian voices. The grackles have descended upon my oaks.
They do so every year at about this time, October and November. And herein lie my questions. How do they know when it is time to visit? What mysterious instinct tells them when shingle and pin oak acorns have ripened? By what strange skill are they able to identify the oaks among the maples, hickories, and poplars which surround them? Clearly, they possess these abilities. I listen to the steady rain of small, round acorns plopping onto the undergrowth, pinging off the metal roof of the garage, and peppering my driveway. Many must be consumed by the birds, but their aggressive frenzy of feeding results in seemingly just as many being mishandled and dropped.
Birds certainly have a keen sense of sight. Perhaps the grackles detect a color change in the acorns which signals ripeness. This occurs with many kinds of berry-producing plants. But I have not noticed the grackles periodically scouting for signs of the edibility of the acorns. They seem to simply show up en masse and gorge themselves.
Could it be that the oaks, which retain their leaves in the fall after other trees have shed theirs, stand out like a beacon for the birds? Surely this could be a possibility later in the season. But the grackles often come while both oaks and surrounding trees bear leaves.
As a student, I was taught that birds have a very poor sense of smell. 
Ornithologists have now discovered that most birds have a decent ability to discern odors, and some have an exceptionally keen sense of smell. The turkey vulture can locate, by smell, a rotting animal carcass a mile away for example. Could it be that the odor of ripe acorns, carried upon the wind, can be detected by my grackle visitors?
I remain both puzzled and fascinated. But then again, the living world is replete with illustrations of sensory accomplishments which leave me astonished. Here are some examples.
The European robin has a magnetoreceptor pigment called cryptochrome in the retinas of its eyes.
This compound is sensitive to earth’s magnetic field. It allows these birds to “see”, in some yet to be understood, mysterious way,
our planet’s magnetic field magnetic field. Perhaps their field of vision is flooded with some particular hue depending upon their compass heading. What a nifty skill this would be for migratory navigation!
The strange, duck-like bill of the platypus is actually a highly complex 
nervous system organ. This so-called rostrum, armed with thousands of mechanical and electrical sensors, can detect the movements as well as the bioelectric aura of their prey. Thus, their bill allows them to hunt and capture prey such as aquatic insects, worms, and crustaceans even in opaque, murky waters. Can you imagine being able to detect another person, stealthily hiding in a totally darkened room, by sensing the bioelectric aura pulsing over their skin surface?
Our oceans represent immense stretches of featureless, pathless, aquatic 
terrain. Yet some animals exhibit the uncanny ability to traverse these vast seas and arrive at a desired spot just as a potential food source becomes abundant. Consider the tiger shark. With a length that may exceed sixteen feet, it is one of the ocean’s largest apex predators.
French Frigate Shoals is a group of islands within the Papahānaumokuākea Marine National Monument. They lie between Kaui and Midway, almost 600 miles northwest of Honolulu and nearly 3000 miles west of the coast of California. In other words, they are extremely remote. Nevertheless, in July and August, tiger sharks congregate in the shallows of French Frigate Shoals.
They are here because this is the precise time of year when albatross chicks, which have fledged on the islands, are learning to fly. Their early flights are weak, short, and somewhat uncoordinated. As a result, these training flights often result in a landing upon the sea just offshore. Patrolling these waters in anticipation of just such an event are tiger sharks.
But my question is, how do the sharks know when and where to gather in order to partake of this avian buffet? The answer is unknown. One marine biologist hypothesizes that the sharks have some sort of internal clock which alerts them to the timing of the albatrosses’ first flights. If so, how have they acquired this clock? Was it initially an accidental discovery that was then encoded into memory and perhaps passed on to offspring?
Speculation has been made that the sharks have stored in their memory banks what might be called resource maps. Could the sharks, much as we might visualize the routes to be taken on a winter get away to Florida, envisage the pathway to this seasonal food source? How so over such a trackless water world? Do the tiger sharks possess some uncanny, undiscovered ability to navigate?
Could they perhaps be sensing Earth’s geomagnetic field and using it as a compass? This seems like a possibility as we know that sharks have bioelectric receptors called ampullae of Lorenzini concentrated on their heads. Maybe these not only detect prey but serve as magnetoreceptors. Are there odors held within ocean currents which direct them on their way? Could the angles of sunlight or moonlight upon the water give navigational clues? Great are the mysteries of the deep.
Then there are the puzzles of animal communication to consider. In the late 1990’s Caitlan O’Connell-Rodwell discovered that African elephants could communicate using seismic waves transmitted through the ground. Special receptors in their feet allow the elephants to detect distant running, stopping, or aggressive charging by their compatriots. In addition, she found that elephants produce very low frequency (infrasonic), airborne vocal sounds. Such sounds are below the threshold of human hearing. This type of sound also produces vibrations in the ground. Thus, elephants can use both their ears and feet as organs of hearing. Infrasounds can be perceived from distances as great as five or six miles. This allows elephants to communicate even when far out of sight of one another. What they may be saying remains to be understood. They have really big brains. One might suspect conversations of significant complexity.
And then there is the possibility that communication among animals may be far more cryptic and inscrutable than the use of very low frequency sounds. I wonder and I do so because of some curious observations of gray wolves mentioned in the late Barry Lopez’s fascinating book Of Wolves and Men.
Wolves are apex predators, literally top “dogs”. They hunt in packs because of their focus upon very large, potentially dangerous prey species such as moose. Mammalian predators in general are highly intelligent and clever. They are keen observers of the behaviors displayed by their target animals. Predators are quick to note prey which have an injured limb, exhibit unnatural posture, move in an uncoordinated manner, or emit the odor of an infected wound. Such signs reveal a lessened ability to defend against attack.
But according to Lopez the interaction of predator and prey, wolf and 
moose in this case, may be based upon something other than these obviously debilitating conditions. Whether a moose appears healthy or not, there is often an initial, face to face meeting with its foe. Wolf and prey remain stationary as they share an intense stare with one another. What may happen next is often curious. After this period of seemingly cross-species assessment the wolf, or wolves, may simply turn and walk off. In other cases, it is the moose that calmly wanders away from a wolf pack. Alternatively the moose may choose to run, in which case it will almost assuredly be attacked. In other cases, after the stare-down, the wolves may suddenly charge and kill the moose within minutes.
Lopez describes such encounters in this way (my underline): I called this exchange in which animals appear to lock eyes and make a decision the conversation of death . . . In this way both animals, not the predator alone, choose for the encounter to end in death. There is, at least, a sacred order in this. There is nobility. And it is something that happens only between the wolf and his major prey species.
Is there indeed some sort of mutual exchange of insight between wolf and moose? Is a concession on the part of one or the other really being made? Are the wolf and moose communicating an understanding, a treaty of death? Or was Mr. Lopez simply attributing human emotions to non-human animals, a classic case of our human tendency to anthropomorphize? Perhaps we will never know.
But really, to encounter organisms with senses which are so remarkable as to leave us dumbfounded, we don’t have to travel to the far reaches of the planet, nor dwell on the possibility that animals can share thoughts.
The mosquito that pesters us here in Indiana, has likely located us from a significant distance by sensing the thirty or forty parts per million of carbon dioxide we have exhaled with each breath. The tick that latched onto us this spring while mushroom hunting did so by sensing the tiny signature of our 
warmth and body odor as we passed by. A tree in a nearby forest under attack by insects may transmit airborne, organic, chemical warning signals to its nearby neighbors. In response, these trees may begin to preemptively produce their own toxic or foul-tasting anti-insect defensive compounds.
As you can imagine, the list of extraordinary, and often mysterious, ways in which organisms use their strange super-senses to operate within their environments are voluminous. It really is a remarkable world in which we live. And, it is worth noting that observation and contemplation of these wonders of nature are there for anyone with a modicum of curiosity. They represent a no-cost, readily at hand, escape from the perplexities, anxieties, and obligations of modern life.
I hope I am granted the boon to stand, again next fall, in bewildered amazement as rush of wings and raucous dialog announce that the grackles have descended upon my oaks. The feathered storm will remind me once more that I live in a world of remarkable mystery, astounding complexity, and endless fascination.
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Photo Credits:
By the author – African elephant, Yellowstone wolf pair, moose, long-horned beetle
grackle by MDF at commons.wikimedia.org
turkey vulture by Dori at commons.wikimedia.org
European robin by Francis Franklin at commons.wikimedia.org
platypus by Lamiot at commons.wikimedia.org
tiger shark by Alber Kok at commons.wikimedia.org
A Reference
Lopez, Barry Holstun. 1978. Of Wolves and Men. Charles Scribner’s Sons, New York.
